The USGCRP{{< tbib '84' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} determined that recent droughts and associated heat waves have reached record intensities in some regions of the United States; however, by geographic scale and duration, the 1930s Dust Bowl remains the benchmark drought and extreme heat event in the historical record since 1895 (very high confidence). The confidence is high that drought negatively impacts crop yield and quality, increases the risk of range wildfires, and accelerates the depletion of water supplies (very likely and high confidence).
" evidence: "The Key Message and supporting text summarize extensive evidence documented in the U.S. Global Change Research Program’s (USGCRP) Climate Science Special Report{{< tbib '84' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} indicating increasing drought frequency or severity in many parts of the United States, increased temperature, and increased frost-free days. An increased probability of hot days concurrent with drought has been reported by Mueller and Seneviratne (2012),{{< tbib '235' '77718bdb-b632-4762-b8a5-d4151785f65b' >}} Mazdiyasni and AghaKouchak (2015),{{< tbib '236' '38b0ec9f-8c00-428f-9ec9-6214f617515d' >}} and Diffenbaugh et al. (2015).{{< tbib '107' '89e08a41-6091-45fa-a92e-6168a90a8151' >}} The warming of minimum temperatures (lack of hard freezes) is contributing to expanding ranges for many insect, disease, and weed species.{{< tbib '237' '5aeba9d1-c405-45a2-b259-bd95dcf17a05' >}} Bebber et al. (2013){{< tbib '238' 'b3855765-38da-4fd9-8288-874a43b16607' >}} report an average poleward shift of 2.7 km/year (1.68 miles/year) since 1960 of numerous pests and pathogens.
Agricultural production: Walthall et al. (2012){{< tbib '38' '3baf471f-751f-4d68-9227-4197fdbb6e5d' >}} synthesize a wide body of literature that documents the impacts of climate, including drought, on crop and livestock productivity and on the natural resources that support agricultural production. Marshall et al. 2015{{< tbib '97' 'bc6c6b92-e049-4b86-b772-8d35032d3cb0' >}} also quantified climate change impacts on the yield of major U.S. crops as well as the reduced ability in the future to mitigate drought by irrigation. Havstad et al. (2016){{< tbib '239' 'c779538d-b066-4e38-8527-ff3f7552f26e' >}} describe the resilience of livestock production on rangelands in the Southwest and identify adaptation management strategies needed in an increasingly arid and variable climatic environment. Liang et al. (2017){{< tbib '240' 'c5857041-2594-47cf-a6bc-3fab052fa903' >}} found that total factor productivity (TFP) for the U.S. agriculture sector is related to regional and seasonal temperature and precipitation factors. Rosenzweig et al. (2014){{< tbib '241' 'b84b193b-ca98-479c-b5ef-fe94e5ffd39c' >}} indicated strong negative effects of climate change on crop yields, particularly at higher levels of warming and lower latitudes. While technological improvements have outweighed the aggregate negative impacts of climate to date, projected climate change indicates that U.S. agriculture TFP could drop to pre-1980s levels by 2050. Ray et al. (2015){{< tbib '242' 'dcf14e95-6370-4d19-b975-33fc290cffae' >}} estimate that climate accounts for about one-third of global yield variability.
Crop heat stress: Novick et al. (2016){{< tbib '243' '3a3fae72-1abc-4a9e-a816-02252ac7c6fe' >}} indicate that atmospheric vapor pressure deficits play a critical role in plant function and productivity and that it will become more important at higher temperatures as an independent factor, relative to available soil moisture. For instance, high temperature has been documented to decrease yields of major crops, including wheat, corn, rice, and soybean.{{< tbib '92' '79853924-784a-4bc1-8c47-551d3e6d9bc1' >}},{{
Wildfire and rangelands: Margolis et al. (2017){{< tbib '255' 'a5604aed-9a6f-468e-acf4-f4a0bb574d3e' >}} report that fire scars in tree rings for the years 1599–1899 indicate that large grassland fires in New Mexico are strongly influenced by the current year cool-season moisture, but that fires burning mid-summer to fall are also influenced by monsoon moisture. Wet conditions several years prior to the fire year, resulting in increased fuel load, are also important for spring through late-summer fires. Persistent cool-season drought lasting longer than three years may inhibit fires due to the lack of moisture to replenish surface fuels. Donovan et al. (2017){{< tbib '95' '81917ef2-289f-4700-bc1a-254feb5156e5' >}} reported that wildfires greater than 400 hectares increased from 33.4 ± 5.6 per year during the period 1985–1994 to 116.8 ± 28.8 wildfires per year for the period 2005–2014 and that the total area burned in the Great Plains by large wildfires increased 400%.
Water supply: Dai and Zhao (2017){{< tbib '256' '476ae3ff-66e2-4cea-8e8f-6e9946356ed0' >}} quantify historical trends in drought based on indices derived from the self-calibrated Palmer Drought Severity Index and the Penman–Monteith potential evapotranspiration index. For greater reliability, they compare these results with observed precipitation change patterns, streamflow, and runoff in three different periods: 1950–2012, 1955–2000, and 1980–2012. They indicate that spatially consistent patterns of drying have occurred in many parts of the Americas, that evaporation trends were slightly negative or slightly positive (exclusive of 1950–1980), and that drought has been increasingly linked to increased vapor pressure deficits since the 1980s.
Pest pressures: Integrated pest management is rapidly evolving in the face of intensifying pest challenges to crop production.{{< tbib '257' '9be3da44-0c39-418f-8dbb-1aca0400d6f7' >}} There is considerable capacity for genetic improvement in agricultural crops and livestock breeds, but the ultimate ability to breed increased heat and drought tolerance into germplasm while retaining desired agronomic or horticultural attributes remains uncertain.{{< tbib '258' 'aa176a1e-7be0-4a50-9099-3656f2bb7d42' >}} The ability to breed pest-resistant varieties into a wide range of species to address rapidly evolving disease, insect, and weed species{{< tbib '237' '5aeba9d1-c405-45a2-b259-bd95dcf17a05' >}} is also uncertain.
" href: https://data.globalchange.gov/report/nca4/chapter/agriculture-and-rural-communities/finding/key-message-10-1.yaml identifier: key-message-10-1 ordinal: 1 process: 'Each regional author team organized a stakeholder engagement process to identify the highest-priority concerns, including priorities for agriculture and rural communities. Due to the heterogeneous nature of agriculture and rural communities, the national chapter leads (NCLs) and coauthor team put in place a structured process to gather and synthesize input from the regional stakeholder meetings. Where possible, one or more of the authors or the chapter lead author listened to stakeholder input during regional stakeholder listening sessions. Information about agriculture and rural communities was synthesized from the written reports from each regional engagement workshop. During the all-authors meeting on April 2–3, 2017, the NCL met with authors from each region and other national author teams to identify issues relevant to this chapter. To finalize our regional roll-up, a teleconference was scheduled with each regional author team to discuss agriculture and rural community issues. Most of the regional author teams identified issues related to agricultural productivity, with underlying topics dominated by drought, temperature, and changing seasonality. Grassland wildfire was identified as a concern in the Northern and Southern Great Plains. All regional author teams identified soil and water vulnerabilities as concerns, particularly as they relate to soil and water quality impacts and a depleting water supply, as well as reduced field operation days due to wet soils and an increased risk of soil erosion due to precipitation on frozen soil. Heat stress in rural communities and among agricultural workers was of concern in the Southeast, Southern Great Plains, Northwest, Hawaiʻi and Pacific Islands, U.S. Caribbean, and Northeast. Livestock health was identified as a concern in the Northeast, Midwest, U.S. Caribbean, and Southern Great Plains. Additional health-related concerns were smoke from wildfire, pesticide impacts, allergens, changing disease vectors, and mental health issues related to disasters and climate change. Issues related to the vulnerability and adaptive capacity of rural communities were identified by all regions. Discussions with the regional teams were followed by expert deliberation on the draft Key Messages by the authors and targeted consultation with additional experts. Information was then synthesized into Key Messages, which were refined based on published literature and professional judgment.
' report_identifier: nca4 statement: 'Food and forage production will decline in regions experiencing increased frequency and duration of drought (high confidence). Shifting precipitation patterns, when associated with high temperatures, will intensify wildfires that reduce forage on rangelands, accelerate the depletion of water supplies for irrigation, and expand the distribution and incidence of pests and diseases for crops and livestock (very likely, high confidence). Modern breeding approaches and the use of novel genes from crop wild relatives are being employed to develop higher-yielding, stress-tolerant crops.
' uncertainties: "Drought impacts on crop yields and forage are critical at the farm economic scale and are well documented.{{< tbib '38' '3baf471f-751f-4d68-9227-4197fdbb6e5d' >}},{{
The evidence on increasing precipitation intensity, with the largest increases occurring in the Northeast, is high (very likely, high confidence). The increase in flooding is less certain (likely, medium confidence). The evidence of the impact of precipitation extremes on infrastructure losses, soil erosion, and contaminant transport to water bodies is well established (very likely, high confidence). Based on medium confidence on flooding but high confidence in increasing precipitation intensity and the impacts of precipitation extremes, there is high confidence in this Key Message.
' evidence: "Evidence of long-term changes in precipitation is based on analyses of daily precipitation observations from the National Weather Service’s Cooperative Observer Network.{{< tbib '261' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}
Groisman et al. (2012){{< tbib '262' '5d909426-fab3-4dc8-af56-e5fe414ca97a' >}} reported that for the central United States, the frequency of very heavy precipitation increased by 20% from 1979–2009 compared to 1948–1978. Slater and Villarini (2016){{< tbib '263' 'a0905615-ac31-42ba-a70f-592a5729fdf7' >}} report a significant increase in flooding frequency in the Southern Plains, California, and northern Minnesota; a smaller increase in the Southeast; and a decrease in the Northern Plains and Northwest. Mallakpour and Villarini (2015){{< tbib '264' 'd2af0d06-91aa-4e53-99e1-4dad2ac9195a' >}} report an increasing frequency of flooding in the Midwest, primarily in summer, but find limited evidence of a change in magnitude of flood peaks.
Infrastructure: Severe local storms constituted the largest class of billion-dollar natural disasters from 1980 to 2011, followed by tropical cyclones and nontropical floods.{{< tbib '265' '4fe32146-a968-4dde-8a2b-df2aa2eabdd4' >}} Špitalar et al. (2014){{< tbib '266' '3f57831b-3c94-4ca9-863b-594a81f51b20' >}} evaluate flash floods from 2006 to 2012 and find that the floods with the highest human impacts, based on injuries and fatalities, are associated with small catchment areas in rural areas. Rural areas face particular challenges with road networks and connectivity.{{< tbib '267' '40fd4927-7950-49c8-b022-31a8fbafa9d4' >}}
Soil and water: Soil carbon on agricultural lands is decreased due to land-use change and tillage,{{< tbib '268' 'fecb7170-32c4-498a-95c0-b374d9ce845b' >}},{{
Each regional author team organized a stakeholder engagement process to identify the highest-priority concerns, including priorities for agriculture and rural communities. Due to the heterogeneous nature of agriculture and rural communities, the national chapter leads (NCLs) and coauthor team put in place a structured process to gather and synthesize input from the regional stakeholder meetings. Where possible, one or more of the authors or the chapter lead author listened to stakeholder input during regional stakeholder listening sessions. Information about agriculture and rural communities was synthesized from the written reports from each regional engagement workshop. During the all-authors meeting on April 2–3, 2017, the NCL met with authors from each region and other national author teams to identify issues relevant to this chapter. To finalize our regional roll-up, a teleconference was scheduled with each regional author team to discuss agriculture and rural community issues. Most of the regional author teams identified issues related to agricultural productivity, with underlying topics dominated by drought, temperature, and changing seasonality. Grassland wildfire was identified as a concern in the Northern and Southern Great Plains. All regional author teams identified soil and water vulnerabilities as concerns, particularly as they relate to soil and water quality impacts and a depleting water supply, as well as reduced field operation days due to wet soils and an increased risk of soil erosion due to precipitation on frozen soil. Heat stress in rural communities and among agricultural workers was of concern in the Southeast, Southern Great Plains, Northwest, Hawaiʻi and Pacific Islands, U.S. Caribbean, and Northeast. Livestock health was identified as a concern in the Northeast, Midwest, U.S. Caribbean, and Southern Great Plains. Additional health-related concerns were smoke from wildfire, pesticide impacts, allergens, changing disease vectors, and mental health issues related to disasters and climate change. Issues related to the vulnerability and adaptive capacity of rural communities were identified by all regions. Discussions with the regional teams were followed by expert deliberation on the draft Key Messages by the authors and targeted consultation with additional experts. Information was then synthesized into Key Messages, which were refined based on published literature and professional judgment.
' report_identifier: nca4 statement: 'The degradation of critical soil and water resources will expand as extreme precipitation events increase across our agricultural landscape (high confidence). Sustainable crop production is threatened by excessive runoff, leaching, and flooding, which results in soil erosion, degraded water quality in lakes and streams, and damage to rural community infrastructure (very likely, very high confidence,). Management practices to restore soil structure and the hydrologic function of landscapes are essential for improving resilience to these challenges.
' uncertainties: "Floods are highly variable in space and time,{{< tbib '86' 'a29b612b-8c28-4c93-9c18-19314babce89' >}} and their characteristics are influenced by a number of non-climate factors.{{< tbib '275' 'b8d001bf-c47f-40f8-91f1-a252a46381b8' >}} Groissman et al. (2012){{< tbib '262' '5d909426-fab3-4dc8-af56-e5fe414ca97a' >}} note that the lack of sub-daily data to analyze precipitation intensity means that daily data are normally used, which limits the ability to detect the most intense precipitation rates. While many practices are available to protect soil and reduce nutrient runoff from agricultural lands,{{< tbib '268' 'fecb7170-32c4-498a-95c0-b374d9ce845b' >}},{{
Extreme temperatures are projected to increase even more than average temperatures. The temperatures of extremely cold days and extremely warm days are both projected to increase. Cold waves are projected to become less intense, while heat waves will become more intense (very likely, very high confidence).{{< tbib '293' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}}
Lehner et al. (2017){{< tbib '294' '53448a8f-22bd-4111-8212-b2204e4d4864' >}} indicate a high likelihood and high confidence that there will be increased record-breaking summer temperatures by the end of the century. Evidence of challenges to human and livestock health due to temperature extremes is well established (very likely, very high confidence).
" evidence: "The Key Message and supporting text summarize extensive evidence documented in the USGCRP’s Climate Science Special Report.{{< tbib '84' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}}
Humans: Houghton et al. (2017){{< tbib '274' 'ced8505a-f36f-4c7b-8a0d-ec7f08482297' >}} synthesize the literature that presents strong evidence of climate change impacts on human health in rural areas. Anderson et al. (2018){{< tbib '277' '200c4ff2-90da-45da-bc7a-f4565dbd2fbb' >}} find that heat waves pose risks to human mortality but that the risk associated with any single heat wave depends on many factors, including heat wave length, timing, and intensity. On average, heat waves increase daily mortality risk by approximately 4% in the United States,{{< tbib '278' 'a6714dce-b324-4324-a88e-d31d31fa2d95' >}} but extreme heat waves present significantly higher risks. While research on heat-related morbidity has focused on urban areas, Jagai et al. (2017){{< tbib '279' 'e518fff1-caa5-4ed1-8fdc-b512da7cbe3b' >}} analyzed heat waves in Illinois over 1987–2014 and found that there were 1.16 hospitalizations per 100,000 people in the most rural, thinly populated areas, compared to 0.45 hospitalizations per 100,000 in metropolitan areas. Consequently, a 1.8°F (1°C) increase in maximum monthly temperature was associated with a 0.34 increase in hospitalization rates in rural areas compared to an increase of 0.02 per 100,000 in urbanized counties. The mean cost per hospital stay was $20,050. Fechter-Leggett et al. (2016),{{< tbib '280' '9d4b4e3f-1739-4e8f-ab0b-610dd5276da3' >}} Hess et al. (2014),{{< tbib '281' '7d16ea3a-c4dc-4ebd-8d38-c3d6a64a3e66' >}} and Sugg et al. (2016){{< tbib '282' 'a0403ee4-f787-4078-bcba-64cdd6cc9cb1' >}} also report an elevated risk in rural areas for emergency room visits for heat stress. Additionally, rural areas have a high proportion of outdoor workers who are at additional risk for heat stress.{{< tbib '279' 'e518fff1-caa5-4ed1-8fdc-b512da7cbe3b' >}},{{
Each regional author team organized a stakeholder engagement process to identify the highest-priority concerns, including priorities for agriculture and rural communities. Due to the heterogeneous nature of agriculture and rural communities, the national chapter leads (NCLs) and coauthor team put in place a structured process to gather and synthesize input from the regional stakeholder meetings. Where possible, one or more of the authors or the chapter lead author listened to stakeholder input during regional stakeholder listening sessions. Information about agriculture and rural communities was synthesized from the written reports from each regional engagement workshop. During the all-authors meeting on April 2–3, 2017, the NCL met with authors from each region and other national author teams to identify issues relevant to this chapter. To finalize our regional roll-up, a teleconference was scheduled with each regional author team to discuss agriculture and rural community issues. Most of the regional author teams identified issues related to agricultural productivity, with underlying topics dominated by drought, temperature, and changing seasonality. Grassland wildfire was identified as a concern in the Northern and Southern Great Plains. All regional author teams identified soil and water vulnerabilities as concerns, particularly as they relate to soil and water quality impacts and a depleting water supply, as well as reduced field operation days due to wet soils and an increased risk of soil erosion due to precipitation on frozen soil. Heat stress in rural communities and among agricultural workers was of concern in the Southeast, Southern Great Plains, Northwest, Hawaiʻi and Pacific Islands, U.S. Caribbean, and Northeast. Livestock health was identified as a concern in the Northeast, Midwest, U.S. Caribbean, and Southern Great Plains. Additional health-related concerns were smoke from wildfire, pesticide impacts, allergens, changing disease vectors, and mental health issues related to disasters and climate change. Issues related to the vulnerability and adaptive capacity of rural communities were identified by all regions. Discussions with the regional teams were followed by expert deliberation on the draft Key Messages by the authors and targeted consultation with additional experts. Information was then synthesized into Key Messages, which were refined based on published literature and professional judgment.
' report_identifier: nca4 statement: 'Challenges to human and livestock health are growing due to the increased frequency and intensity of high temperature extremes (very likely, high confidence). Extreme heat conditions contribute to heat exhaustion, heatstroke, and heart attacks in humans (very likely, high confidence). Heat stress in livestock results in large economic losses for producers (very likely, high confidence). Expanded health services in rural areas, heat-tolerant livestock, and improved design of confined animal housing are all important advances to minimize these challenges.
' uncertainties: "Humans: Much of the literature focuses on heat-related mortality in urban areas (e.g., Oleson et al. 2015; Marsha et al. 2017{{< tbib '286' 'a5d430bc-5756-42d1-924f-3dbc927e69c4' >}},{{
Livestock: Walthall et al. (2012){{< tbib '38' '3baf471f-751f-4d68-9227-4197fdbb6e5d' >}} synthesize a wide body of literature that documents the impacts of extreme temperature effects on livestock health and productivity. Ruminant livestock support rural livelihoods and produce high-quality food products from land that is otherwise unsuited to crop agriculture.{{< tbib '291' '831b4c27-416e-4b98-94e6-3969a3b34031' >}},{{
Lower levels of education, poverty, limited infrastructure, and lack of access to resources will limit the adaptive capacity of individuals and communities (very likely, high confidence). Adaptive capacity in rural communities is being increased through federal, state, and local capacity building efforts (likely, low to medium confidence). However, the outreach to rural communities varies greatly in different parts of the United States.
' evidence: "A wealth of data shows that residents of rural areas generally have lower levels of education and lower wages for a given level of education compared to residents of urban areas.{{< tbib '295' '5a980b1c-524c-4a24-9c35-55974a05a0df' >}} Higher levels of poverty, particularly childhood poverty,{{< tbib '7' 'ec982e73-ed8b-460e-9042-e9da15ca84ca' >}} and food insecurity in rural compared to urban areas are also well documented.{{< tbib '49' 'abcd2b28-87f9-499e-9be5-736d6208d3c2' >}} There is also research that documents the disproportionate impacts of climate change on areas with multiple socioeconomic disadvantages, such as an increased risk of exposure to extreme heat and poor air quality, lack of access to basic necessities, and fewer job opportunities.{{< tbib '229' '2fb19c54-72ed-460d-a72f-78f257decd7c' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/agriculture-and-rural-communities/finding/key-message-10-4.yaml identifier: key-message-10-4 ordinal: 4 process: 'Each regional author team organized a stakeholder engagement process to identify the highest-priority concerns, including priorities for agriculture and rural communities. Due to the heterogeneous nature of agriculture and rural communities, the national chapter leads (NCLs) and coauthor team put in place a structured process to gather and synthesize input from the regional stakeholder meetings. Where possible, one or more of the authors or the chapter lead author listened to stakeholder input during regional stakeholder listening sessions. Information about agriculture and rural communities was synthesized from the written reports from each regional engagement workshop. During the all-authors meeting on April 2–3, 2017, the NCL met with authors from each region and other national author teams to identify issues relevant to this chapter. To finalize our regional roll-up, a teleconference was scheduled with each regional author team to discuss agriculture and rural community issues. Most of the regional author teams identified issues related to agricultural productivity, with underlying topics dominated by drought, temperature, and changing seasonality. Grassland wildfire was identified as a concern in the Northern and Southern Great Plains. All regional author teams identified soil and water vulnerabilities as concerns, particularly as they relate to soil and water quality impacts and a depleting water supply, as well as reduced field operation days due to wet soils and an increased risk of soil erosion due to precipitation on frozen soil. Heat stress in rural communities and among agricultural workers was of concern in the Southeast, Southern Great Plains, Northwest, Hawaiʻi and Pacific Islands, U.S. Caribbean, and Northeast. Livestock health was identified as a concern in the Northeast, Midwest, U.S. Caribbean, and Southern Great Plains. Additional health-related concerns were smoke from wildfire, pesticide impacts, allergens, changing disease vectors, and mental health issues related to disasters and climate change. Issues related to the vulnerability and adaptive capacity of rural communities were identified by all regions. Discussions with the regional teams were followed by expert deliberation on the draft Key Messages by the authors and targeted consultation with additional experts. Information was then synthesized into Key Messages, which were refined based on published literature and professional judgment.
' report_identifier: nca4 statement: 'Residents in rural communities often have limited capacity to respond to climate change impacts, due to poverty and limitations in community resources (very likely, high confidence). Communication, transportation, water, and sanitary infrastructure are vulnerable to disruption from climate stressors (very likely, high confidence). Achieving social resilience to these challenges would require increases in local capacity to make adaptive improvements in shared community resources.
' uncertainties: "There is uncertainty about future economic activity and employment in rural U.S. communities. However, the patterns of lower education levels, higher poverty levels, and high unemployment have been persistent and are likely to require long-term, focused efforts to reverse.{{< tbib '6' 'a2a02512-dacf-46f0-8f9f-9cb51892a884' >}},{{
There is very high confidence that the opportunities and resources available in a particular urban area influence the health and well-being of its residents. There is high confidence that climate change exacerbates challenges to aging and deteriorating infrastructure, degrading urban ecosystems, and urban residents’ health and well-being. There is medium confidence that many cities are engaging in creative problem solving to address the challenges to quality of life posed by climate change. The effectiveness of this response depends on many factors (for example, intensity of extreme weather events, stakeholder collaboration, and internal and external resources available).
' evidence: "Urban areas provide resources and opportunities for residents’ quality of life.{{< tbib '145' 'f1f67e52-3ceb-47c9-8961-a6640d15a618' >}},{{
Climate change combines with other trends to increase stress on the health and well-being of urban residents.{{< tbib '10' 'c9bda474-d322-478c-8574-21d8dc7a4f5c' >}},{{
Metropolitan areas often have more resources than rural ones, as reflected in income per capita, employment rates, and workforce education.{{< tbib '178' '96fca595-cfc0-4364-b138-51bd2cceb1b3' >}},{{
Report authors developed this chapter through technical discussions of relevant evidence and expert deliberation and through regular teleconferences, meetings, and email exchanges. For additional information on the overall report process, see App. 1: Process. The author team evaluated scientific evidence from peer-reviewed literature, technical reports, and consultations with professional experts and the public via webinar and teleconferences. The scope of this chapter is urban climate change impacts, vulnerability, and response. It covers the built environment and infrastructure systems in the socioeconomic context of urban areas. This chapter updates findings from the Third National Climate Assessment and advances the understanding of previously identified urban impacts by including emerging literature on urban adaptation and emphasizing how urban social and ecological systems are related to the built environment and infrastructure. The five case-study cities were selected because they represent a geographic diversity of urban impacts from wildfire, sea level rise, heat, and inland flooding. The author team was selected based on their experiences and expertise in the urban sector. They bring a diversity of disciplinary perspectives and have a strong knowledge base for analyzing the complex ways that climate change affects the built environment, infrastructure, and urban systems.
" report_identifier: nca4 statement: 'The opportunities and resources in urban areas are critically important to the health and well-being of people who work, live, and visit there (very high confidence). Climate change can exacerbate existing challenges to urban quality of life, including social inequality, aging and deteriorating infrastructure, and stressed ecosystems (high confidence). Many cities are engaging in creative problem solving to improve quality of life while simultaneously addressing climate change impacts (medium confidence).
' uncertainties: "It is difficult to predict future urban trends with certainty. Many factors influence the size and composition of urban populations, development patterns, social networks, cultural resources, and economic growth.{{< tbib '180' 'ba5cb012-f7fc-420f-924c-be2c0276aa86' >}} The degree to which climate change will exacerbate existing urban vulnerabilities depends in part on the frequency and intensity of extreme weather events,{{< tbib '145' 'f1f67e52-3ceb-47c9-8961-a6640d15a618' >}} which are projected with far less certainty than incremental changes in average conditions.{{< tbib '81' '31bf15ab-c374-4466-8b4c-894a527813cb' >}} Moreover, projections are not often made at the city scale.{{< tbib '185' '8be634e3-a62f-44d2-9cde-dd7010cdad04' >}} Climate change may accelerate urban tree growth, but overall effects on growing conditions depend on a variety of factors.{{< tbib '186' '2234e14a-bfd8-428d-9719-863108d36da8' >}} These uncertainties make it difficult to predict how climate change and other factors will intersect to affect urban quality of life. Furthermore, quality of life is difficult to measure, although some metrics are available.{{< tbib '187' '5b7e5de3-722a-4010-8d86-44e9722e3da9' >}}
Urban climate vulnerability depends on local social, political, demographic, environmental, and economic characteristics.{{< tbib '59' '3c3cc09b-c2d7-4c52-bf8f-c064efa78e93' >}},{{
There is very high confidence that the integrity of urban infrastructure is and will continue to be threatened by exposure to climate change stressors (for example, more frequent and extreme precipitation events, sea level rise, and heat) and that damages from weather events demonstrate infrastructure vulnerability. Many urban areas have endured high costs from such events, and many of those costs can be attributed to infrastructure failures or damages. There is very high confidence that urban infrastructure will need to endure a future climate that is different from the past in order to fulfill its long service life. There is high confidence that investment in forward-looking design provides a foundation for reliable infrastructure that can withstand ongoing and future climate risks. How much implementing forward-looking design will reduce risks is less clear, since much depends on other factors such as changes in urban population, social inequalities, the broader economy, and rates of climate change.
' evidence: "There is wide agreement that architects, engineers, and city planners need to consider a range of future climate conditions in urban infrastructure design to guarantee that assets perform for the duration of their expected service lives.{{< tbib '14' '87a21f64-2fec-4057-afa4-30bb29e09104' >}},{{
Numerous studies document substantial economic damages in urban areas following extreme weather events and predict an increase in damages through time as these events occur with greater frequency and intensity.{{< tbib '14' '87a21f64-2fec-4057-afa4-30bb29e09104' >}},{{
Report authors developed this chapter through technical discussions of relevant evidence and expert deliberation and through regular teleconferences, meetings, and email exchanges. For additional information on the overall report process, see App. 1: Process. The author team evaluated scientific evidence from peer-reviewed literature, technical reports, and consultations with professional experts and the public via webinar and teleconferences. The scope of this chapter is urban climate change impacts, vulnerability, and response. It covers the built environment and infrastructure systems in the socioeconomic context of urban areas. This chapter updates findings from the Third National Climate Assessment and advances the understanding of previously identified urban impacts by including emerging literature on urban adaptation and emphasizing how urban social and ecological systems are related to the built environment and infrastructure. The five case-study cities were selected because they represent a geographic diversity of urban impacts from wildfire, sea level rise, heat, and inland flooding. The author team was selected based on their experiences and expertise in the urban sector. They bring a diversity of disciplinary perspectives and have a strong knowledge base for analyzing the complex ways that climate change affects the built environment, infrastructure, and urban systems.
" report_identifier: nca4 statement: 'Damages from extreme weather events demonstrate current urban infrastructure vulnerabilities (very high confidence). With its long service life, urban infrastructure must be able to endure a future climate that is different from the past (very high confidence). Forward-looking design informs investment in reliable infrastructure that can withstand ongoing and future climate risks (high confidence).
' uncertainties: "There are gaps in our understanding of the performance capacity of existing structures exposed to climate change stressors and of the available resources and commitment (at the state, local, tribe, and federal level) to implement forward-looking designs in investments.{{< tbib '192' '7be3e21c-fdd2-47ee-bc70-d8458792c662' >}},{{
The extent to which key climate stressors will change over the design life of urban systems and structures is uncertain. It depends on the rate of global climate change as well as regional and local factors.{{< tbib '150' '3e9b6eba-21a7-474e-9773-190a0ec18257' >}},{{
There is very high confidence that urban areas rely on essential goods and services that are vulnerable to climate change because they are part of interdependent networks of infrastructure, ecosystems, and social systems. There is high confidence that extreme weather events have resulted in adverse cascading effects across urban sectors and systems, as there is documentation of a significant number of case studies of urban areas demonstrating these effects. It is projected with medium confidence that network damages from future climate change will disrupt many aspects of urban life, given that the complexity of urban life and the many factors affecting urban resilience to climate change make future disruptions difficult to predict. Similarly, there is medium confidence that addressing interconnected vulnerabilities via coordinated efforts can build urban resilience to climate change.
' evidence: "Research focusing on urban areas shows that climate change has or is anticipated to have a net negative effect on transportation,{{< tbib '43' 'd2f3853a-5f20-4132-92c8-57da1b4d95fc' >}},{{
Researchers have modeled and documented how negative effects on one system that provides urban goods and services cascade into others that rely on it.{{< tbib '3' 'ce2db20d-ff1b-407c-873e-fde134a7929c' >}},{{
The literature shows that coordinated resilience planning across sectors and jurisdictions to address interdependencies involves using models and plans,{{< tbib '3' 'ce2db20d-ff1b-407c-873e-fde134a7929c' >}},{{
Report authors developed this chapter through technical discussions of relevant evidence and expert deliberation and through regular teleconferences, meetings, and email exchanges. For additional information on the overall report process, see App. 1: Process. The author team evaluated scientific evidence from peer-reviewed literature, technical reports, and consultations with professional experts and the public via webinar and teleconferences. The scope of this chapter is urban climate change impacts, vulnerability, and response. It covers the built environment and infrastructure systems in the socioeconomic context of urban areas. This chapter updates findings from the Third National Climate Assessment and advances the understanding of previously identified urban impacts by including emerging literature on urban adaptation and emphasizing how urban social and ecological systems are related to the built environment and infrastructure. The five case-study cities were selected because they represent a geographic diversity of urban impacts from wildfire, sea level rise, heat, and inland flooding. The author team was selected based on their experiences and expertise in the urban sector. They bring a diversity of disciplinary perspectives and have a strong knowledge base for analyzing the complex ways that climate change affects the built environment, infrastructure, and urban systems.
" report_identifier: nca4 statement: 'Interdependent networks of infrastructure, ecosystems, and social systems provide essential urban goods and services (very high confidence). Damage to such networks from current weather extremes and future climate will adversely affect urban life (medium confidence). Coordinated local, state, and federal efforts can address these interconnected vulnerabilities (medium confidence).
' uncertainties: "Interconnections among urban systems have been studied less extensively than climate change effects on individual urban sectors, and there are still gaps to be filled.{{< tbib '239' 'b093b04e-26ca-4957-9fad-165e46d763bb' >}},{{
While it has been demonstrated that climate change affects urban systems, the extent to which climate change will affect a given urban system is difficult to predict. It depends on the unique strengths and vulnerabilities of that system as well as the regional and local climate conditions to which the system is exposed.{{< tbib '110' '15c8ad4d-f96a-4bfb-8944-63d220e42f3b' >}},{{
The severity of future climate impacts and cascading consequences for urban networks depends on the magnitude of global climate change.{{< tbib '223' '00e98394-26f1-45da-a5a3-e79b2b1a356f' >}} Urban systems may be able to tolerate some levels of stress with only minor disruptions. Stresses of greater frequency, longer duration, or greater intensity may compromise a system’s ability to function.{{< tbib '36' 'aba07260-60ad-44df-9810-29f23f46facd' >}},{{
There is high confidence that municipal governments and other institutions in many U.S. cities are planning and implementing climate change adaptation and mitigation actions. There is high confidence that urban adaptation and mitigation can provide additional near-term benefits, although the distribution of benefits and harms within cities is uneven. There is medium confidence in the effect these actions have and will have on current and future climate change impacts. If cities take only small actions, they are unlikely to fully protect urban residents from devastating impacts, particularly given projected levels of climate change. There is high confidence that cities face challenges in responding to climate change and that when cities build on local knowledge, use risk management approaches, explicitly address social vulnerability, and participate in multicity networks, their ability to respond to climate change is improved. The degree of improvement depends on other factors that affect urban response outcomes.
' evidence: "Multiple review studies have documented that cities in all parts of the United States are undertaking adaptation and mitigation actions.{{< tbib '45' '60233f20-d45f-4086-ada7-00dbd47712c3' >}},{{
Numerous studies have examined the ways in which adaptation actions reduce the impacts of weather extremes in urban areas. Documented benefits include reductions in urban heat risk{{< tbib '48' '133d9f9c-e1fd-4c50-b349-67eef6048291' >}},{{
Report authors developed this chapter through technical discussions of relevant evidence and expert deliberation and through regular teleconferences, meetings, and email exchanges. For additional information on the overall report process, see App. 1: Process. The author team evaluated scientific evidence from peer-reviewed literature, technical reports, and consultations with professional experts and the public via webinar and teleconferences. The scope of this chapter is urban climate change impacts, vulnerability, and response. It covers the built environment and infrastructure systems in the socioeconomic context of urban areas. This chapter updates findings from the Third National Climate Assessment and advances the understanding of previously identified urban impacts by including emerging literature on urban adaptation and emphasizing how urban social and ecological systems are related to the built environment and infrastructure. The five case-study cities were selected because they represent a geographic diversity of urban impacts from wildfire, sea level rise, heat, and inland flooding. The author team was selected based on their experiences and expertise in the urban sector. They bring a diversity of disciplinary perspectives and have a strong knowledge base for analyzing the complex ways that climate change affects the built environment, infrastructure, and urban systems.
" report_identifier: nca4 statement: 'Cities across the United States are leading efforts to respond to climate change (high confidence). Urban adaptation and mitigation actions can affect current and projected impacts of climate change and provide near-term benefits (medium confidence). Challenges to implementing these plans remain. Cities can build on local knowledge and risk management approaches, integrate social equity concerns, and join multicity networks to begin to address these challenges (high confidence).
' uncertainties: "While urban adaptation actions can reduce the effects of extreme weather, there is uncertainty regarding the effectiveness of these actions against future climate change.{{< tbib '115' 'e092ae8f-d7ed-4879-8773-ea442b9fd12d' >}},{{
Research on drivers of and challenges to urban response is in the incipient stage, with divergent results about social and political requirements for effective response.{{< tbib '114' '98a171ed-c572-4c28-a49b-03110f1cac10' >}},{{
There is very high confidence that sea level rise and increases in flooding during coastal storms and astronomical high tides will lead to damage and service reductions with coastal bridges, roads, rails, and ports.
There is high confidence that heavy precipitation events have increased in intensity and frequency since 1901 (with the largest increase seen in the Northeast); this trend is projected to continue.{{< tbib '25' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} There is medium confidence that precipitation increases will lead to surface and rail transit delays in urban areas. There is medium confidence that flood-induced damages to roads and bridges will increase.
Rising temperatures and extreme heat (high confidence) will damage pavement and increase railway and air transit delays. However, the actual magnitude of those impacts will depend on technological advancements and policy decisions about design and operations.
" evidence: "Global mean sea level has risen since 1900 and is expected to continue to rise.{{< tbib '2' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} High tide flooding is increasing{{< tbib '1' '91aeffdb-e82f-4645-abe9-f6ea6909e979' >}} and is projected to continue increasing.{{< tbib '1' '91aeffdb-e82f-4645-abe9-f6ea6909e979' >}} The peak storm surge levels are expected to rise more than the rise in sea level; models show that if the depth of storm flooding today is A and the rise in sea level between now and a future occurrence of an identical storm is B, then the resulting future storm surge depths can be greater than A + B.{{< tbib '52' 'b19545a1-2e63-458c-8497-32a6d023aa89' >}} The U.S. roads and bridges in the coastal floodplain{{< tbib '49' 'aae26529-edab-4278-8fe1-5763251ddb97' >}} are vulnerable today, as storms are repeatedly causing damage.{{< tbib '50' 'c4151050-1289-41b6-a2ac-b760afe3c98b' >}},{{
In most parts of the United States, heavy precipitation is increasing in frequency and intensity, and more severe precipitation events are anticipated in the future.{{< tbib '25' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} Inland transportation infrastructure is highly vulnerable to intense rainfall and flooding.{{< tbib '3' 'bde3292e-b7bb-4a48-b2ea-40a594f37eb5' >}},{{
The frequency of summer heat waves has increased since the 1960s, and average annual temperatures have increased over the past three decades; these temperature changes are projected to continue to increase in the future.{{< tbib '41' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}} Warming temperatures have increased costs{{< tbib '81' 'cd7183d0-7e06-4d08-bba2-3765b2eba3fe' >}} and reduced the performance of roads,{{< tbib '80' '7088ab60-2e3b-484f-811e-3590848901e6' >}} bridges,{{< tbib '4' '50d04578-d18d-4401-9b14-87b507319741' >}},{{
We sought an author team that could bring diverse experiences and perspectives to the chapter, including some who have participated in prior national-level assessments within the sector. All are experts in the field of climate adaptation and transportation infrastructure. The team represents geographic expertise in the Northeast, Mid-Atlantic, South, Central, and Western regions, including urban and rural as well as coastal and inland perspectives. Team members come from the public (federal and city government and academia) and private sectors (consulting and engineering), with practitioner and research backgrounds.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops and teleconferences and via email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations with transportation experts during multiple listening sessions.
Because the impacts of climate change on transportation assets for the United States and globally have been widely examined elsewhere, including in the Third National Climate Assessment (NCA3),{{< tbib '137' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} this chapter addresses previously identified climate change impacts on transportation assets that persist nationally, with a focus on recent literature that describes newly identified impacts and advances in understanding. Asset vulnerability and impacts are of national importance because there are societal and economic consequences that transcend regional or subregional boundaries when a transportation network fails to perform as designed; a chapter focus is the emerging understanding of those impacts. Further, place-based, societally relevant understanding of transportation system resilience has been strongly informed by numerous recent local and state assessments that capture regionally relevant climate impacts on transportation and collectively inform national level risks and resilience. The chapter synthesizes the transportation communities’ national awareness of and readiness for climate threats that are most relevant in the United States.
A reliable, safe, and efficient U.S. transportation system is at risk from increases in heavy precipitation, coastal flooding, heat, wildfires, and other extreme events, as well as changes to average temperature (high confidence). Throughout this century, climate change will continue to pose a risk to U.S. transportation infrastructure, with regional differences (high confidence).
' uncertainties: "Peer-reviewed literature on climate impacts to some assets is limited. Most literature addresses local- or regional-scale issues. Uncertainty in the ranges of climate change projection leads to challenges to quantifying impacts on transportation assets, which have long lifetimes.
Impacts to transportation infrastructure from climate change will depend on many factors, including population growth, economic demands, policy decisions, and technological changes. How these factors, with their potential compounding effects, as well as the impacts of disruptive or transformative technologies (such as automated vehicles or autonomous aerial vehicles), will contribute to transportation performance in the future is poorly understood.
The relationship among increases in large precipitation events and flood-induced infrastructure damage is uncertain because multiple factors (including land use, topography, and even flood control) impact flooding.{{< tbib '140' 'a36df8f5-949c-412c-8371-e5a5b139c757' >}},{{
There is medium to high confidence that the urban setting can amplify heat.{{< tbib '159' '1b0ce605-0f6c-4e1f-8fea-71e87cb4304f' >}} There is also medium to high confidence that transportation networks are impacted by inland and coastal flooding.{{< tbib '70' 'a29b612b-8c28-4c93-9c18-19314babce89' >}} There is medium confidence that socioeconomic conditions are strongly related to a population’s resilience to extreme events.{{< tbib '151' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}}
There is high confidence that impacts to the transportation network from extreme events are inducing societal and economic consequences, some of which disproportionately affect vulnerable populations (medium confidence). In the absence of intervention, projected changes in climate will likely lead to increasing transportation challenges as a result of system complexity, aging infrastructure with hundreds of billions of dollars in rehabilitation backlogs,{{< tbib '13' '9115ee8c-84a2-43a3-96dc-09b6fcacc03f' >}} and dependency across sectors.
" evidence: "The Key Message is largely supported by observation and empirical evidence that is well documented in the gray (non-peer-reviewed) literature and recent government reports. Because this is an important emerging area of research, the peer-reviewed scientific literature is sparse. Hence, much of the supporting materials for this Key Message are descriptions of impacts of recent events provided by news organizations and government summaries.
Many urban locations have experienced disruptive extreme events that have impacted the transportation network and led to societal and economic consequences. Louisiana experienced historic floods in 2016 that disrupted all modes of transportation and caused adverse impacts on major industries and businesses due to the halt of freight movement and employees’ inability to get to work.{{< tbib '146' '772e841e-180a-47f8-a799-500647586c00' >}} The 2016 floods that affected Texas from March to June resulted in major business disruption due to the loss of a major transportation corridor.{{< tbib '147' '741b9a22-f7c4-42b7-ad5c-405165add8b5' >}} In 2017, Hurricane Harvey affected population and freight mobility in Houston, Texas, when 23 ports were closed and over 700 roads were deemed impassable.{{< tbib '148' 'f40f0b46-1b69-49d1-915e-d191f590c87f' >}} Consequences of extreme events can be magnified when events are cumulative. The 2017 hurricanes impacting the southern Atlantic and Gulf Coasts and Puerto Rico created rising freight costs because freight carriers had to deal with poor traveling conditions, an unreliable fuel stock, and limited exports for the return trip.{{< tbib '149' '63f91a03-3377-4198-b856-0e35d0673a35' >}},{{
Similar to the urban and suburban scenarios, rural areas across the country have also experienced disruptions and impacts from climate events. Hurricane Irene resulted in the damage or destruction of roads throughout New England, resulting in small towns being isolated throughout the region.{{< tbib '152' 'e6a71298-6e58-4b80-b3e9-750385b9cc4d' >}} Similarly, Hurricane Katrina devastated rural community infrastructure across the Gulf Coast, which resulted in extended periods of isolation and population movement.{{< tbib '153' '6e1d67c5-05d5-4094-a5e6-1a854e3a47cf' >}} Lesser-known events are also causing regular impacts to rural communities, such as flood events in 2014 in Minnesota and in 2017 throughout the Midwest, which impacted towns for months due to damaged road infrastructure.{{< tbib '154' 'a6f2252d-d6b9-407d-9757-f8ce76fe282e' >}},{{
Although flooding events and hurricanes receive significant attention, other weather-based events cause equal or greater impacts to rural areas. Landslide events have isolated rural communities by reducing them to single-road access.{{< tbib '156' '83683960-a588-4670-ad1a-819ae28689ee' >}},{{
As documented, rural communities incur impacts from climate events that are similar to those experienced in urban and suburban communities. However, rural and isolated areas experience the additional concerns of recovering from extreme events with fewer resources and less capacity.{{< tbib '111' '52ba053e-57fc-4767-8273-c605b19a0c2c' >}} This difference often results in rural communities facing extended periods of time with limited access for commercial and residential traffic.
" href: https://data.globalchange.gov/report/nca4/chapter/transportation/finding/key-message-12-2.yaml identifier: key-message-12-2 ordinal: 2 process: "We sought an author team that could bring diverse experiences and perspectives to the chapter, including some who have participated in prior national-level assessments within the sector. All are experts in the field of climate adaptation and transportation infrastructure. The team represents geographic expertise in the Northeast, Mid-Atlantic, South, Central, and Western regions, including urban and rural as well as coastal and inland perspectives. Team members come from the public (federal and city government and academia) and private sectors (consulting and engineering), with practitioner and research backgrounds.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops and teleconferences and via email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations with transportation experts during multiple listening sessions.
Because the impacts of climate change on transportation assets for the United States and globally have been widely examined elsewhere, including in the Third National Climate Assessment (NCA3),{{< tbib '137' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} this chapter addresses previously identified climate change impacts on transportation assets that persist nationally, with a focus on recent literature that describes newly identified impacts and advances in understanding. Asset vulnerability and impacts are of national importance because there are societal and economic consequences that transcend regional or subregional boundaries when a transportation network fails to perform as designed; a chapter focus is the emerging understanding of those impacts. Further, place-based, societally relevant understanding of transportation system resilience has been strongly informed by numerous recent local and state assessments that capture regionally relevant climate impacts on transportation and collectively inform national level risks and resilience. The chapter synthesizes the transportation communities’ national awareness of and readiness for climate threats that are most relevant in the United States.
Extreme events that increasingly impact the transportation network are inducing societal and economic consequences, some of which disproportionately affect vulnerable populations (high confidence). In the absence of intervention, future changes in climate will lead to increasing transportation challenges, particularly because of system complexity, aging infrastructure, and dependency across sectors (high confidence).
' uncertainties: 'Realized societal and economic impacts from transportation disruptions vary by extreme event, depending on the intensity and duration of the storm; pre-storm conditions, including cumulative events; planning mechanisms (such as zoning practices); and so on. In addition, a combination of weather stressors, such as heavy precipitation with notable storm surge, can amplify effects on different assets, compounding the societal and economic consequences. These amplifications are poorly understood but directly affect transportation users. Interdependencies among transportation and other lifeline sectors can also have significant impacts on the degree of consequences experienced. These impacts are also poorly understood.
' uri: /report/nca4/chapter/transportation/finding/key-message-12-2 url: ~ - chapter_identifier: transportation confidence: 'There is high confidence regarding the efforts of state and local transportation agencies to understand climate impacts through assessments like those referenced in Figure 12.3. There is medium confidence in the reasons for delay in implementing resilience measures and the motivations for vulnerability assessments. There is no consensus on how emerging transportation technologies will develop in the coming years and how this change will affect climate mitigation, adaptation, and resilience.
' evidence: 'Chapter authors reviewed more than 60 recently published vulnerability assessments (details and links available through the online version of Figure 12.3) conducted by or for states and localities. The research approach involved internet searches, consultations with experts, and leveraging existing syntheses and compilations of transportation-related vulnerability assessments. The authors cast a broad net to ensure that as many assessments as possible were captured in the review. The studies were screened for a variety of metrics (for example, method of assessment, hazard type, asset category, vulnerability assessment type, economic analysis, and adaptation actions), and findings were used to inform the conclusions reached in this section.
' href: https://data.globalchange.gov/report/nca4/chapter/transportation/finding/key-message-12-3.yaml identifier: key-message-12-3 ordinal: 3 process: "We sought an author team that could bring diverse experiences and perspectives to the chapter, including some who have participated in prior national-level assessments within the sector. All are experts in the field of climate adaptation and transportation infrastructure. The team represents geographic expertise in the Northeast, Mid-Atlantic, South, Central, and Western regions, including urban and rural as well as coastal and inland perspectives. Team members come from the public (federal and city government and academia) and private sectors (consulting and engineering), with practitioner and research backgrounds.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops and teleconferences and via email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations with transportation experts during multiple listening sessions.
Because the impacts of climate change on transportation assets for the United States and globally have been widely examined elsewhere, including in the Third National Climate Assessment (NCA3),{{< tbib '137' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} this chapter addresses previously identified climate change impacts on transportation assets that persist nationally, with a focus on recent literature that describes newly identified impacts and advances in understanding. Asset vulnerability and impacts are of national importance because there are societal and economic consequences that transcend regional or subregional boundaries when a transportation network fails to perform as designed; a chapter focus is the emerging understanding of those impacts. Further, place-based, societally relevant understanding of transportation system resilience has been strongly informed by numerous recent local and state assessments that capture regionally relevant climate impacts on transportation and collectively inform national level risks and resilience. The chapter synthesizes the transportation communities’ national awareness of and readiness for climate threats that are most relevant in the United States.
Engineers, planners, and researchers in the transportation field are showing increasing interest and sophistication in understanding the risks that climate hazards pose to transportation assets and services (very high confidence). Transportation practitioner efforts demonstrate the connection between advanced assessment and the implementation of adaptive measures, though many communities still face challenges and barriers to action (high confidence).
' uncertainties: 'Most of the literature and the practitioner studies cited for Key Message 3 were gray literature, which is not peer-reviewed but serves the purpose of documenting the state of the practice. This section was not an assessment of the science (that is, the validity of individual study results was not assessed) but surveyed how transportation practitioners are assessing and managing climate impacts. The conclusions are not predicated on selection of or relative benefits of specific modeling or technological advances.
Practitioners’ motivations underlying changes in the state of the practice were derived from information in the studies and from cited literature. The authors of this section did not survey authors of individual vulnerability studies to determine their situation-specific motivations.
' uri: /report/nca4/chapter/transportation/finding/key-message-12-3 url: ~ - chapter_identifier: air-quality confidence: 'There is high confidence that rising temperatures will likely increase future ozone levels in many parts of the United States in response to climate change. There is greater uncertainty that a warmer climate will increase future PM2.5 levels over the United States. Ultimately, the actual ozone and PM2.5 changes between the present and the future at any given location will depend on the local climate impacts on meteorology and pollutant emission controls in that region. There is very high confidence that reducing ozone precursor emissions and PM2.5 precursors and/or direct emissions will likely lead to improved air quality in the future, thus mitigating adverse climate effects.
' evidence: "It is well established that air pollutants pose a serious risk to human health and the environment.{{< tbib '5' 'f7ffc8dd-70ec-4779-817a-b2985c0779e7' >}},{{
Due to limited resources and requirements imposed by the Federal Advisory Committee Act, the decision was made that this chapter would be developed using an all-federal author team. The author team was selected based on expertise in climate change impacts on air quality; several of the chapter authors were authors of the “Air Quality Impacts” chapter of the U.S. Global Change Research Program’s (USGCRP) Climate and Health Assessment.{{< tbib '3' '5ec155e5-8b77-438f-afa9-fbcac4d27690' >}} This chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors via weekly teleconferences and email exchanges. The authors considered inputs and comments submitted by the public; the National Academies of Sciences, Engineering, and Medicine; and federal agencies.
More than 100 million people in the United States live in communities where air pollution exceeds health-based air quality standards. Unless counteracting efforts to improve air quality are implemented, climate change will worsen existing air pollution levels (likely, high confidence). This worsened air pollution would increase the incidence of adverse respiratory and cardiovascular health effects, including premature death (high confidence). Increased air pollution would also have other environmental consequences, including reduced visibility and damage to agricultural crops and forests (likely, very high confidence).
' uncertainties: "Model simulations of future air quality indicate that climate warming generally increases ground-level ozone across the United States (see Figure 13.2), but results differ spatially and in the magnitude of the projected signal.{{< tbib '90' '8168dfd7-c53f-4e89-ba22-991d6a2179a6' >}},{{
There is high confidence that rising temperatures and earlier spring snowmelt will very likely result in lengthening the wildfire season in portions of the United States, leading to an increased frequency of wildfires and associated smoke. There is very high confidence that increasing exposure to wildfire smoke, which contains particulate matter, will increase adverse health impacts. It is likely that smoke from wildfires will reduce visibility and disrupt outdoor recreational activities.
' evidence: "Wildfire smoke worsens air quality through its direct emissions to the atmosphere as well as through chemical reactions of those pollutants with sunlight and other pollutants. Exposure to wildfire smoke increases the risk of exacerbating respiratory illnesses in tens of millions of people in vulnerable population groups across the United States.{{< tbib '62' '9a222c75-5ff9-408e-9694-b7bd90a2a0ca' >}} Several studies have indicated that climate change has already led to longer wildfire seasons,{{< tbib '79' 'e1e1f3a0-9fea-4ad2-a3af-575716f9849e' >}} increased frequency of large wildfires,{{< tbib '82' 'd96a729a-a5db-4318-8f52-78f6031b42fd' >}},{{
Due to limited resources and requirements imposed by the Federal Advisory Committee Act, the decision was made that this chapter would be developed using an all-federal author team. The author team was selected based on expertise in climate change impacts on air quality; several of the chapter authors were authors of the “Air Quality Impacts” chapter of the U.S. Global Change Research Program’s (USGCRP) Climate and Health Assessment.{{< tbib '3' '5ec155e5-8b77-438f-afa9-fbcac4d27690' >}} This chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors via weekly teleconferences and email exchanges. The authors considered inputs and comments submitted by the public; the National Academies of Sciences, Engineering, and Medicine; and federal agencies.
Wildfire smoke degrades air quality, increasing the health risks to tens of millions of people in the United States. More frequent and severe wildfires due to climate change would further diminish air quality, increase incidences of respiratory illness from exposure to wildfire smoke, impair visibility, and disrupt outdoor recreational activities (very likely, high confidence).
' uncertainties: "Humans affect fire activity in many ways, including increasing ignitions as well as conducting controlled burns and fire suppression activities.{{< tbib '110' '415d7f4d-4e24-4cff-a9aa-c76f30dbeb42' >}},{{
The scientific literature shows that there is high confidence that changes in climate, including rising temperatures and altered precipitation patterns as well as rising levels of atmospheric CO2, will increase the concentration, allergenicity, season length, and spatial distribution of a number of aeroallergens. These changes in aeroallergen exposure are, in turn, likely to impact allergic disease.
' evidence: "Considerable evidence supports the conclusion that climate change and rising levels of CO2 affect key aspects of aeroallergen biology, including the production, temporal distribution, and potential allergenicity of aeroallergens.{{< tbib '142' '14835bc7-3df6-4fac-9e9a-2863c09e800a' >}},{{
Specific changes in weather patterns or extremes are also likely to contribute to the exacerbation of allergy symptoms. For example, thunderstorms can induce spikes in aeroallergen concentrations and increase the incidence and severity of asthma and other allergic disease.{{< tbib '148' '713cd919-826b-426d-bf51-761a58ec7f22' >}},{{
Overall, climate change and rising CO2 levels are likely to increase exposure to aeroallergens and contribute to the severity and prevalence of allergic disease, including asthma.{{< tbib '115' '971ee908-7da0-416e-8b6c-a72984d129ba' >}} There is consistent and compelling evidence that exposure to aeroallergens poses a significant health risk in regard to the occurrence of asthma, hay fever, sinusitis, conjunctivitis, hives, and anaphylaxis.{{< tbib '150' '036ba27d-8341-4f6d-ad66-1288e53dee65' >}},{{
Due to limited resources and requirements imposed by the Federal Advisory Committee Act, the decision was made that this chapter would be developed using an all-federal author team. The author team was selected based on expertise in climate change impacts on air quality; several of the chapter authors were authors of the “Air Quality Impacts” chapter of the U.S. Global Change Research Program’s (USGCRP) Climate and Health Assessment.{{< tbib '3' '5ec155e5-8b77-438f-afa9-fbcac4d27690' >}} This chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors via weekly teleconferences and email exchanges. The authors considered inputs and comments submitted by the public; the National Academies of Sciences, Engineering, and Medicine; and federal agencies.
The frequency and severity of allergic illnesses, including asthma and hay fever, are likely to increase as a result of a changing climate. Earlier spring arrival, warmer temperatures, changes in precipitation, and higher carbon dioxide concentrations can increase exposure to airborne pollen allergens. (Likely, High Confidence)
' uncertainties: "While specific climate- and/or CO2-induced links to aeroallergen biology are evident, allergic diseases develop in response to complex and multiple interactions, including genetic and nongenetic factors, a developing immune system, environmental exposures (such as ambient air pollution or weather conditions), and socioeconomic and demographic factors. Overall, the role of these factors in eliciting a health response has not been entirely elucidated. However, recent evidence suggests that climate change and aeroallergens are having a discernible impact on public health.{{< tbib '123' 'c9c2ea5f-223f-4594-b182-40b473c6e665' >}},{{
There are a number of areas where additional information is needed, including regional variation in climate and aeroallergen production; specific links between aeroallergens and related diseases, particularly asthma; the need for standardized approaches to determine exposure times and pollen concentration; and uncertainty regarding the role of CO2 on allergenicity.
" uri: /report/nca4/chapter/air-quality/finding/key-message-13-3 url: ~ - chapter_identifier: air-quality confidence: 'There is very high confidence that emissions of ozone and PM precursors could be reduced by reducing combustion sources of CO2. Reducing emissions of ozone and PM precursors would be very likely to reduce ozone and PM pollution, which would very likely result in fewer adverse health effects from air pollution. There is very high confidence that controlling methane emissions would also reduce ozone formation rates, which would also very likely lead to lower ozone levels.
' evidence: 'Decades of experience in air quality management have resulted in a detailed accounting of the largest emission sources of greenhouse gases (GHGs) and precursors of ozone and PM. The cost and effectiveness of emission control technologies for the largest emissions sources are well understood. By combining these emission and control technology data with energy system modeling tools, the potential to achieve benefits to air quality while mitigating GHG emissions under a range of scenarios has been quantified in numerous studies.
' href: https://data.globalchange.gov/report/nca4/chapter/air-quality/finding/key-message-13-4.yaml identifier: key-message-13-4 ordinal: 4 process: "Due to limited resources and requirements imposed by the Federal Advisory Committee Act, the decision was made that this chapter would be developed using an all-federal author team. The author team was selected based on expertise in climate change impacts on air quality; several of the chapter authors were authors of the “Air Quality Impacts” chapter of the U.S. Global Change Research Program’s (USGCRP) Climate and Health Assessment.{{< tbib '3' '5ec155e5-8b77-438f-afa9-fbcac4d27690' >}} This chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors via weekly teleconferences and email exchanges. The authors considered inputs and comments submitted by the public; the National Academies of Sciences, Engineering, and Medicine; and federal agencies.
Many emission sources of greenhouse gases also emit air pollutants that harm human health. Controlling these common emission sources would both mitigate climate change and have immediate benefits for air quality and human health. Because methane is both a greenhouse gas and an ozone precursor, reductions of methane emissions have the potential to simultaneously mitigate climate change and improve air quality. (Very Likely, Very High Confidence)
' uncertainties: 'A wide range of values have been reported for the magnitude of air quality co-benefits. Much of this variability can be attributed to differences in the mix of co-benefits included in the analysis and the time period under consideration. The largest sources of uncertainty are the cost paths of different energy technologies over time and the extent to which policy choices impact the evolution of these costs and the availability of different energy technologies.
' uri: /report/nca4/chapter/air-quality/finding/key-message-13-4 url: ~ - chapter_identifier: human-health confidence: 'There is very high confidence that climate change is affecting the health of Americans. There is high confidence that climate-related health risks, without additional adaptation and mitigation, will likely increase with additional climate change.
' evidence: "Multiple lines of evidence demonstrate statistically significant associations between temperature, precipitation, and other variables and adverse climate-sensitive health outcomes, indicating sensitivity to weather patterns.{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} These lines of evidence also demonstrate that vulnerability varies across sub-populations and geographic areas; populations with higher vulnerability include poor people in high-income regions, minority groups, women, children, the disabled, those living alone, those with poor health status, Indigenous people, older adults, outdoor workers, people displaced because of weather and climate, low-income residents that lack a social network, poorly planned communities, communities disproportionately burdened by poor environmental quality, the disenfranchised, those with less access to healthcare, and those with limited financial resources to rebound from disasters.{{< tbib '108' 'b9638744-8ff8-41bd-a741-27b2fda9face' >}},{{
The chapter evaluated the scientific evidence of the health risks of climate change, focusing primarily on the literature published since the cut off date (approximately fall 2015) of the U.S. Climate and Health Assessment.{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} A comprehensive literature search was performed by federal contractors in December 2016 for studies published since January 1, 2014, using PubMed, Scopus, and Web of Science. An Excel file containing 2,477 peer-reviewed studies was provided to the author team for it to consider in this assessment. In addition to the literature review, the authors considered recommended studies submitted in comments by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The focus of the literature was on health risks in the United States, with limited citations from other countries providing insights into risks Americans are or will likely face with climate change. A full description of the search strategy can be found at https://www.niehs.nih.gov/CCHH_Search_Strategy_NCA4_508.pdf. The chapter authors were chosen based on their expertise in the health risks of climate change. Teleconferences were held with interested researchers and practitioners in climate change and health and with authors in other chapters of this Fourth National Climate Assessment (NCA4).
The U.S. Climate and Health Assessment{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} did not consider adaptation or mitigation, including economic costs and benefits, so the literature cited includes research from earlier years where additional information was relevant to this assessment.
For NCA4, Air Quality was added as a report chapter. Therefore, while Key Messages in this Health chapter include consideration of threats to human health from worsened air quality, the assessment of these risks and impacts are covered in Chapter 13: Air Quality. Similarly, co-benefits of reducing greenhouse gas emissions are covered in the Air Quality chapter.
" report_identifier: nca4 statement: 'The health and well-being of Americans are already affected by climate change (very high confidence), with the adverse health consequences projected to worsen with additional climate change (likely, high confidence). Climate change affects human health by altering exposures to heat waves, floods, droughts, and other extreme events; vector-, food- and waterborne infectious diseases; changes in the quality and safety of air, food, and water; and stresses to mental health and well-being.
' uncertainties: 'The role of non-climate factors, including socioeconomic conditions, population characteristics, and human behavior, as well as health sector policies and practices, will continue to make it challenging to attribute injuries, illnesses, and deaths to climate change. Inadequate consideration of these factors creates uncertainties in projections of the magnitude and pattern of health risks over coming decades. Certainty is higher in near-term projections where there is greater understanding of future trends.
' uri: /report/nca4/chapter/human-health/finding/key-message-14-1 url: ~ - chapter_identifier: human-health confidence: 'There is high confidence that climate change is disproportionately affecting the health of children, older adults, low-income communities, communities of color, tribal and Indigenous communities, and many other distinct populations. And there is high confidence that some of the most vulnerable populations experience greater barriers to accessing resources, information, and tools to build resilience.
' evidence: "Multiple lines of evidence demonstrate that low-income communities and some communities of color are experiencing higher rates of exposure to adverse environmental conditions and social conditions that can reduce their resilience to the impacts of climate change.{{< tbib '106' 'c76d7935-9da3-4c4b-9186-86dc658bcc74' >}},{{
Adaptation can increase the climate resilience of populations when the process of developing and implementing policies and measures includes understanding the ethical and human rights dimensions of climate change, meeting human needs in a sustainable and equitable way, and engaging with representatives of the most impacted communities to assess the challenges they face and to define the climate solutions.{{< tbib '124' '7f89e40a-7681-4475-a754-91e81baabd95' >}},{{
The chapter evaluated the scientific evidence of the health risks of climate change, focusing primarily on the literature published since the cut off date (approximately fall 2015) of the U.S. Climate and Health Assessment.{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} A comprehensive literature search was performed by federal contractors in December 2016 for studies published since January 1, 2014, using PubMed, Scopus, and Web of Science. An Excel file containing 2,477 peer-reviewed studies was provided to the author team for it to consider in this assessment. In addition to the literature review, the authors considered recommended studies submitted in comments by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The focus of the literature was on health risks in the United States, with limited citations from other countries providing insights into risks Americans are or will likely face with climate change. A full description of the search strategy can be found at https://www.niehs.nih.gov/CCHH_Search_Strategy_NCA4_508.pdf. The chapter authors were chosen based on their expertise in the health risks of climate change. Teleconferences were held with interested researchers and practitioners in climate change and health and with authors in other chapters of this Fourth National Climate Assessment (NCA4).
The U.S. Climate and Health Assessment{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} did not consider adaptation or mitigation, including economic costs and benefits, so the literature cited includes research from earlier years where additional information was relevant to this assessment.
For NCA4, Air Quality was added as a report chapter. Therefore, while Key Messages in this Health chapter include consideration of threats to human health from worsened air quality, the assessment of these risks and impacts are covered in Chapter 13: Air Quality. Similarly, co-benefits of reducing greenhouse gas emissions are covered in the Air Quality chapter.
" report_identifier: nca4 statement: 'People and communities are differentially exposed to hazards and disproportionately affected by climate-related health risks (high confidence). Populations experiencing greater health risks include children, older adults, low-income communities, and some communities of color (high confidence).
' uncertainties: "The role of non-climate factors, including socioeconomic conditions, discrimination (racial and ethnic, gender, persons with disabilities), psychosocial stressors, and the continued challenge to measure the cumulative effects of past, present, and future environmental exposures on certain people and communities will continue to make it challenging to attribute injuries, illnesses, and deaths to climate change. While there is no universal framework for building more resilient communities that can address the unique situations across the United States, factors integral to community resilience include the importance of social networks, the value of including community voice in the planning and execution of solutions, and the co-benefits of institutional readiness to address the physical, health, and social needs of impacted communities. These remain hard to quantify.{{< tbib '127' 'cab3885c-a808-40f4-9b4a-79808bbdf202' >}},{{
There is medium confidence that with sufficient human and financial resources, adaptation policies and programs can reduce the current burden of climate-sensitive health outcomes.{{< tbib '110' '289728b3-ae8b-417e-920e-96af1a5e64b3' >}},{{
Health adaptation is taking place from local to national scales.{{< tbib '129' 'a6d2d472-b084-4805-9f08-cc5e1f95f668' >}},{{
The chapter evaluated the scientific evidence of the health risks of climate change, focusing primarily on the literature published since the cut off date (approximately fall 2015) of the U.S. Climate and Health Assessment.{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} A comprehensive literature search was performed by federal contractors in December 2016 for studies published since January 1, 2014, using PubMed, Scopus, and Web of Science. An Excel file containing 2,477 peer-reviewed studies was provided to the author team for it to consider in this assessment. In addition to the literature review, the authors considered recommended studies submitted in comments by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The focus of the literature was on health risks in the United States, with limited citations from other countries providing insights into risks Americans are or will likely face with climate change. A full description of the search strategy can be found at https://www.niehs.nih.gov/CCHH_Search_Strategy_NCA4_508.pdf. The chapter authors were chosen based on their expertise in the health risks of climate change. Teleconferences were held with interested researchers and practitioners in climate change and health and with authors in other chapters of this Fourth National Climate Assessment (NCA4).
The U.S. Climate and Health Assessment{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} did not consider adaptation or mitigation, including economic costs and benefits, so the literature cited includes research from earlier years where additional information was relevant to this assessment.
For NCA4, Air Quality was added as a report chapter. Therefore, while Key Messages in this Health chapter include consideration of threats to human health from worsened air quality, the assessment of these risks and impacts are covered in Chapter 13: Air Quality. Similarly, co-benefits of reducing greenhouse gas emissions are covered in the Air Quality chapter.
" report_identifier: nca4 statement: 'Proactive adaptation policies and programs reduce the risks and impacts from climate-sensitive health outcomes and from disruptions in healthcare services (medium confidence). Additional benefits to health arise from explicitly accounting for climate change risks in infrastructure planning and urban design (low confidence).
' uncertainties: "Overall, while there is considerable evidence of the effectiveness of public health programs,{{< tbib '110' '289728b3-ae8b-417e-920e-96af1a5e64b3' >}},{{
There is a high confidence that a reduction in greenhouse gas emissions would benefit the health of Americans. There is medium confidence that reduced greenhouse gas emissions under RCP4.5 compared to RCP8.5 will likely reduce lost labor hours by almost half and avoid thousands of premature deaths and illnesses projected each year from climate impacts on extreme heat, ozone and aeroallergen levels (Ch. 13: Air Quality), and West Nile neuroinvasive disease. There is medium confidence that the economic benefits of greenhouse gas emissions reductions in the health sector could likely be on the order of hundreds of billions of dollars each year by the end of the century. Including avoided or reduced benefits of risks that are difficult to quantify, such as mental health or long-term health consequences, would increase these estimates.
" evidence: "Benefits of mitigation associated with air quality, including co-benefits of reducing greenhouse gas emissions, can be found in Chapter 13: Air Quality. This Key Message is consistent with and inclusive of those findings.
Multiple individual lines of evidence across several health topic areas demonstrate significant benefits of greenhouse gas emission reductions, with health impacts and health-related costs reduced by approximately half under RCP4.5 compared to RCP8.5 by the end of the century, based on comprehensive multisector quantitative analyses of economic impacts projected under consistent scenarios (Ch. 13: Air Quality).{{< tbib '37' '4308e866-5976-4181-8102-24b521ff4033' >}},{{
Heat: Greenhouse gas emission reductions under RCP4.5 could substantially reduce the annual number of heat wave days (for example, by 21 in the Northwest and by 43 in the Southeast by the end of the century);{{< tbib '161' 'a5d430bc-5756-42d1-924f-3dbc927e69c4' >}} the number of high-mortality heat waves;{{< tbib '162' 'f9703346-dc6b-4b3e-aad6-2643c74f5292' >}},{{
Labor productivity: Hsiang et al. (2017){{< tbib '167' 'fad9e8ec-8951-4daa-9a9c-e093ef86af16' >}} and the EPA (2017){{< tbib '157' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} estimated the number of labor hours from changes in extreme temperatures using dose–response functions for the relationship between temperature and labor from Graff Zivin and Neidell (2014).{{< tbib '169' '8f2308d0-7a25-4c47-82e0-cb9196f1de8b' >}} Under RCP8.5, almost 2 billion labor hours are projected to be lost annually by 2090 from the impacts of extreme heat and cold, costing an estimated $160 billion in lost wages. The Southeast{{< tbib '164' 'bbca6337-718b-4289-b6e7-0a2f6c1cb8f1' >}},{{
Vector-borne disease: Belova et al. (2017){{< tbib '37' '4308e866-5976-4181-8102-24b521ff4033' >}} and the EPA (2017){{< tbib '157' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} define health impact functions from regional associations between temperatures and the probability of above-average West Nile neuroinvasive disease (WNND) incidence to estimate county-level expected WNND incidence rates for a 1995 reference period (1986–2005) and two future years (2050: 2040–2059 and 2090: 2080–2099) using temperature data from five GCMs. Annual national cases of WNND are projected to more than double by 2050 due to increasing temperatures, resulting in approximately $1 billion per year in hospitalization costs and premature deaths. In 2090, an additional 3,300 annual cases are projected under RCP8.5, with $3.3 billion per year in costs. Greenhouse gas emission reductions under RCP4.5 could avoid approximately half these cases and costs.
Water quality: Chapra et al. (2017){{< tbib '165' '28077cd1-c29f-48ae-a068-2cdcef880807' >}} and the EPA (2017){{< tbib '157' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} evaluate the biophysical impacts of climate change on the occurrence of cyanobacterial harmful algal blooms in the contiguous United States using models that project rainfall runoff, water demand, water resources systems, water quality, and algal growth. In 2090, warming under RCP8.5 is projected to increase the length of time that recreational waters have concentrations of harmful algal blooms (cyanobacteria) above the recommended public health threshold by one month annually; greenhouse gas emissions under RCP4.5 could reduce this by two weeks.
Food safety and nutrition: There is limited evidence quantifying specific health outcomes or economic impacts of reduced food safety and nutrition.
" href: https://data.globalchange.gov/report/nca4/chapter/human-health/finding/key-message-14-4.yaml identifier: key-message-14-4 ordinal: 4 process: "The chapter evaluated the scientific evidence of the health risks of climate change, focusing primarily on the literature published since the cut off date (approximately fall 2015) of the U.S. Climate and Health Assessment.{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} A comprehensive literature search was performed by federal contractors in December 2016 for studies published since January 1, 2014, using PubMed, Scopus, and Web of Science. An Excel file containing 2,477 peer-reviewed studies was provided to the author team for it to consider in this assessment. In addition to the literature review, the authors considered recommended studies submitted in comments by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The focus of the literature was on health risks in the United States, with limited citations from other countries providing insights into risks Americans are or will likely face with climate change. A full description of the search strategy can be found at https://www.niehs.nih.gov/CCHH_Search_Strategy_NCA4_508.pdf. The chapter authors were chosen based on their expertise in the health risks of climate change. Teleconferences were held with interested researchers and practitioners in climate change and health and with authors in other chapters of this Fourth National Climate Assessment (NCA4).
The U.S. Climate and Health Assessment{{< tbib '1' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} did not consider adaptation or mitigation, including economic costs and benefits, so the literature cited includes research from earlier years where additional information was relevant to this assessment.
For NCA4, Air Quality was added as a report chapter. Therefore, while Key Messages in this Health chapter include consideration of threats to human health from worsened air quality, the assessment of these risks and impacts are covered in Chapter 13: Air Quality. Similarly, co-benefits of reducing greenhouse gas emissions are covered in the Air Quality chapter.
" report_identifier: nca4 statement: 'Reducing greenhouse gas emissions would benefit the health of Americans in the near and long term (high confidence). By the end of this century, thousands of American lives could be saved and hundreds of billions of dollars in health-related economic benefits gained each year under a pathway of lower greenhouse gas emissions (likely, medium confidence).
' uncertainties: 'While projections consistently indicate that changes in climate are expected to have negative health consequences, quantifying specific health outcomes (for example, number of cases, number of premature deaths) remains challenging, as noted in Key Message 1. Economic estimates only partially capture and monetize impacts across each health topic area, which means that damage costs are likely to be an undervaluation of the actual health impacts that would occur under any given scenario. Economic estimates in this chapter do not include costs to the healthcare system.
' uri: /report/nca4/chapter/human-health/finding/key-message-14-4 url: ~ - chapter_identifier: tribal-and-indigenous-communities confidence: 'Given the amount of robust and consistent studies in the literature, the authors have very high confidence that Indigenous peoples’ subsistence and commercial livelihoods and economies, including agriculture, hunting and gathering, fishing, forestry, recreation, tourism, and energy, face current threats from climate impacts to water, land, and other natural resources, as well as infrastructure and related human systems and services. The authors have high confidence in the available evidence indicating that it is likely that future climate change will increase impacts to water, land, other natural resources, and infrastructure that support Indigenous people’s livelihoods and economies. The authors have high confidence that Indigenous peoples’ economies depend on, but face institutional barriers to, their self-determined management of water, land, other natural resources, and infrastructure, stemming from funding constraints and the complexities of federal oversight of trust resources.
' evidence: "Multiple studies of Indigenous peoples in the United States provide consistent and high-quality evidence that climate change is both a current and future threat to Indigenous livelihoods and economies. The climate impacts on traditional subsistence economies and hunting and gathering activities have been extensively documented and consistently provide qualitative observational evidence of impacts.{{< tbib '4' '6eef5a47-4a5e-4d07-88d4-b3cdff9bf9a0' >}},{{
Multiple studies also consistently identify funding constraints as barriers to the economic development of federally and non-federally recognized tribes,{{< tbib '21' '02b02533-c288-4eff-b88a-eb4ac3c61df4' >}},{{
The studies cited above consistently conclude that these impacts on livelihoods and economies will increase under future projections of climate change. However, methods for making these determinations vary, and quantitative or modeling results that are specific to Indigenous peoples in the United States are limited.
" href: https://data.globalchange.gov/report/nca4/chapter/tribal-and-indigenous-communities/finding/key-message-15-1.yaml identifier: key-message-15-1 ordinal: 1 process: 'The report authors developed this chapter through technical discussions of relevant evidence and expert deliberation via several meetings, teleconferences, and email exchanges between the spring of 2016 and June 2017. The authors considered inputs and comments submitted by the public in response to the U.S. Global Change Research Program’s (USGCRP) Federal Register Notices, as well as public input provided through regional engagement workshops and engagement webinars. The author team also considered comments provided by experts within federal agencies through a formal interagency review process.
Additional efforts to solicit input for the chapter were undertaken in 2016–2017. The Bureau of Indian Affairs (BIA) worked with partners, the College of Menominee Nation, and the Salish Kootenai College to develop and execute an outreach plan for the chapter. This included awarding mini-grants for community meetings in the fall of 2016 and attending and presenting at tribally focused meetings such as the American Indian Higher Education Consortium 2016 Student Conference (March 2016), the Annual National Conference of the Native American Fish and Wildlife Society (May 2016), the National Tribal Forum on Air Quality (May 2016), the workshops of Rising Voices (2016, 2017), the Native Waters on Arid Lands Tribal Summit (November 2017), the BIA Tribal Providers Conference in Alaska (November 2017), and the Tribes & First Nations Summit (December 2017), among others. Additionally, through these tribal partners, the BIA provided 28 travel scholarships to interested tribal partners to attend and comment on the initial draft content of all regional chapters at the USGCRP’s regional engagement workshops. Additional avenues to communicate during these formal open-comment periods included multiple webinars, website notices on the BIA Tribal Resilience Program page, and email notices through BIA and partner email lists. In particular, the BIA solicited comments from multiple tribal partners on the completeness of the online interactive version of the map in Figure 15.1. Chapter authors and collaborators also presented at interactive forums with tribal representatives, such as the National Adaptation Forum (2017), and in various webinars to extend awareness of formal requests for comment opportunities through the USGCRP and partners, such as the Pacific Northwest Tribal Climate Change Network. The feedback and reports from these activities were used to ensure that the Key Messages and supporting text included the most prominent topics and themes.
' report_identifier: nca4 statement: 'Climate change threatens Indigenous peoples’ livelihoods and economies, including agriculture, hunting and gathering, fishing, forestry, energy, recreation, and tourism enterprises (very high confidence). Indigenous peoples’ economies rely on, but face institutional barriers to, their self-determined management of water, land, other natural resources, and infrastructure (high confidence) that will be impacted increasingly by changes in climate (likely, high confidence).
' uncertainties: "As with all prospective studies, there is some uncertainty inherent in modeled projections of future changes, including both global climate system models and economic sector models. In addition, none of the cited studies explicitly modeled the effects of climate adaptation actions in the relevant economic sectors and the extent to which such actions may reduce Indigenous vulnerabilities.
The literature currently lacks studies that attempt to quantify and/or monetize climate impacts on Indigenous economies or economic activities. Instead, the studies cited above in the “Description of evidence base” section are qualitative analyses. The chapter references Chapter 29: Mitigation for some quantitative studies about climate impacts to U.S. economic sectors, but these are not specifically about Indigenous economies. Quantitative national studies of climate impacts may have general applicability to Indigenous peoples, but their overall utility in quantifying impacts to Indigenous peoples may be limited, because there is uncertainty regarding the extent to which appropriate extrapolations can be made between Indigenous and non-Indigenous contexts.
Other uncertainties include characterizing future impacts and vulnerabilities in a shifting policy landscape, when vulnerabilities can be either exacerbated or alleviated in part by policy changes, such as the quantification and adjudication of federal reserved water rights and the development of policies that promote or inhibit the development of adaptation and mitigation strategies (for example, the development of water rights for instream flow purposes).{{< tbib '19' '84368091-876c-4474-93de-50d64e88cf56' >}}
" uri: /report/nca4/chapter/tribal-and-indigenous-communities/finding/key-message-15-1 url: ~ - chapter_identifier: tribal-and-indigenous-communities confidence: 'Based on available evidence, the authors have high confidence that Indigenous health is based on interconnected social and ecological systems that are being disrupted by a changing climate. The authors have high confidence in the available evidence indicating that it is likely that future climate change will increase impacts to lands, waters, foods, and other plant and animal species and that Indigenous health will be uniquely challenged by these impacts. The authors have high confidence, based on the quality of available evidence, that the lands, waters, foods, and other natural resources and species are foundational to Indigenous peoples’ cultural heritages, identities, and physical and mental health due to their essential role in maintaining Indigenous peoples’ sites, practices, and relationships with cultural, spiritual, or ceremonial importance.
' evidence: "Multiple epidemiological studies provide consistent and high-quality evidence that Indigenous peoples face health disparities according to conventional Western science approaches to assessing health risk; in general, Indigenous peoples have disproportionately higher rates of asthma,{{< tbib '90' '5a3ba94b-e83c-4f01-8156-d4b018006d0c' >}} cardiovascular disease,{{< tbib '91' 'f5751fe0-05cf-47eb-8e47-3d84a1949c76' >}},{{
Additionally, a number of qualitative studies consistently find that Indigenous health, adaptive capacity, and health disparities/environmental justice issues typically do not capture many of the key elements of health and resilience that are important to Indigenous populations, which include concepts related to community connection, natural resources security, cultural use, education and knowledge, self-determination, and autonomy.{{< tbib '81' '98957f73-e40a-4a1e-b48d-01108d939123' >}},{{
The studies consistently conclude that these adverse impacts to culture,{{< tbib '61' '5eff7771-5f15-43c7-8a4c-4383cac47316' >}},{{
There is consistent evidence from behavioral and public health research showing that responses to extreme heat serve as examples of climate change adaptation.{{< tbib '108' '99ab656c-36e4-4410-b5b3-7a6a360e6fa0' >}},{{
The report authors developed this chapter through technical discussions of relevant evidence and expert deliberation via several meetings, teleconferences, and email exchanges between the spring of 2016 and June 2017. The authors considered inputs and comments submitted by the public in response to the U.S. Global Change Research Program’s (USGCRP) Federal Register Notices, as well as public input provided through regional engagement workshops and engagement webinars. The author team also considered comments provided by experts within federal agencies through a formal interagency review process.
Additional efforts to solicit input for the chapter were undertaken in 2016–2017. The Bureau of Indian Affairs (BIA) worked with partners, the College of Menominee Nation, and the Salish Kootenai College to develop and execute an outreach plan for the chapter. This included awarding mini-grants for community meetings in the fall of 2016 and attending and presenting at tribally focused meetings such as the American Indian Higher Education Consortium 2016 Student Conference (March 2016), the Annual National Conference of the Native American Fish and Wildlife Society (May 2016), the National Tribal Forum on Air Quality (May 2016), the workshops of Rising Voices (2016, 2017), the Native Waters on Arid Lands Tribal Summit (November 2017), the BIA Tribal Providers Conference in Alaska (November 2017), and the Tribes & First Nations Summit (December 2017), among others. Additionally, through these tribal partners, the BIA provided 28 travel scholarships to interested tribal partners to attend and comment on the initial draft content of all regional chapters at the USGCRP’s regional engagement workshops. Additional avenues to communicate during these formal open-comment periods included multiple webinars, website notices on the BIA Tribal Resilience Program page, and email notices through BIA and partner email lists. In particular, the BIA solicited comments from multiple tribal partners on the completeness of the online interactive version of the map in Figure 15.1. Chapter authors and collaborators also presented at interactive forums with tribal representatives, such as the National Adaptation Forum (2017), and in various webinars to extend awareness of formal requests for comment opportunities through the USGCRP and partners, such as the Pacific Northwest Tribal Climate Change Network. The feedback and reports from these activities were used to ensure that the Key Messages and supporting text included the most prominent topics and themes.
' report_identifier: nca4 statement: 'Indigenous health is based on interconnected social and ecological systems that are being disrupted by a changing climate (high confidence). As these changes continue, the health of individuals and communities will be uniquely challenged by climate impacts to lands, waters, foods, and other plant and animal species (likely, high confidence). These impacts threaten sites, practices, and relationships with cultural, spiritual, or ceremonial importance that are foundational to Indigenous peoples’ cultural heritages, identities, and physical and mental health (high confidence).
' uncertainties: "The literature currently lacks national-scale studies that quantify and/or monetize climate impacts on Indigenous health, either through traditional Western science health metrics or Indigenous values-based metrics and indicators of health. There are quantitative studies of specific health-relevant topics, such as climate impacts to air quality (Ch. 13: Air Quality) or extreme heat (Ch. 29: Mitigation), but health impact models have not to date been used to model Indigenous population-specific climate impacts. Quantitative national studies of climate impacts may have general applicability to Indigenous peoples, but their overall utility in quantifying impacts to Indigenous peoples may be limited, because there is uncertainty regarding the extent to which appropriate extrapolations can be made between Indigenous and non-Indigenous contexts. In addition, none of the studies explicitly modeled the effects of climate adaptation actions and the extent to which such actions may reduce Indigenous vulnerabilities or projected future impacts.
Other uncertainties include characterizing future impacts and vulnerabilities in a shifting policy landscape, in which vulnerabilities can be either exacerbated or alleviated in part by policy or programmatic changes, such as a recognition of the non-physiological aspects of Indigenous health.
" uri: /report/nca4/chapter/tribal-and-indigenous-communities/finding/key-message-15-2 url: ~ - chapter_identifier: tribal-and-indigenous-communities confidence: 'Based on the quality of available evidence, the authors have very high confidence that Indigenous peoples are proactively identifying and addressing climate impacts but that many face various obstacles limiting their implementation of adaptation practices. There is high confidence that successful adaptation in Indigenous contexts leverages Indigenous knowledge, robust social systems and protocols, and a commitment to Indigenous self-determination.
' evidence: "There is robust documentation of ongoing Indigenous adaptation to climate variability and change.{{< tbib '1' 'd3ebe118-8e13-4c66-af22-b50a8a707360' >}},{{
a limited capacity to implement adaptation strategies,{{< tbib '19' '84368091-876c-4474-93de-50d64e88cf56' >}},{{
limited access to traditional territory and resources,{{< tbib '6' '1421b069-116f-4263-a4f7-e80db0ed74bd' >}},{{
limitations of existing policies, programs, and funding mechanisms.{{< tbib '6' '1421b069-116f-4263-a4f7-e80db0ed74bd' >}},{{
There are many studies that provide evidence with medium consensus that effective participatory planning processes for environmental decision-making (such as for sustainable land management or climate adaptation) are guided by Indigenous knowledge and resilient and robust social systems and protocols).{{< tbib '6' '1421b069-116f-4263-a4f7-e80db0ed74bd' >}},{{
The report authors developed this chapter through technical discussions of relevant evidence and expert deliberation via several meetings, teleconferences, and email exchanges between the spring of 2016 and June 2017. The authors considered inputs and comments submitted by the public in response to the U.S. Global Change Research Program’s (USGCRP) Federal Register Notices, as well as public input provided through regional engagement workshops and engagement webinars. The author team also considered comments provided by experts within federal agencies through a formal interagency review process.
Additional efforts to solicit input for the chapter were undertaken in 2016–2017. The Bureau of Indian Affairs (BIA) worked with partners, the College of Menominee Nation, and the Salish Kootenai College to develop and execute an outreach plan for the chapter. This included awarding mini-grants for community meetings in the fall of 2016 and attending and presenting at tribally focused meetings such as the American Indian Higher Education Consortium 2016 Student Conference (March 2016), the Annual National Conference of the Native American Fish and Wildlife Society (May 2016), the National Tribal Forum on Air Quality (May 2016), the workshops of Rising Voices (2016, 2017), the Native Waters on Arid Lands Tribal Summit (November 2017), the BIA Tribal Providers Conference in Alaska (November 2017), and the Tribes & First Nations Summit (December 2017), among others. Additionally, through these tribal partners, the BIA provided 28 travel scholarships to interested tribal partners to attend and comment on the initial draft content of all regional chapters at the USGCRP’s regional engagement workshops. Additional avenues to communicate during these formal open-comment periods included multiple webinars, website notices on the BIA Tribal Resilience Program page, and email notices through BIA and partner email lists. In particular, the BIA solicited comments from multiple tribal partners on the completeness of the online interactive version of the map in Figure 15.1. Chapter authors and collaborators also presented at interactive forums with tribal representatives, such as the National Adaptation Forum (2017), and in various webinars to extend awareness of formal requests for comment opportunities through the USGCRP and partners, such as the Pacific Northwest Tribal Climate Change Network. The feedback and reports from these activities were used to ensure that the Key Messages and supporting text included the most prominent topics and themes.
' report_identifier: nca4 statement: 'Many Indigenous peoples have been proactively identifying and addressing climate impacts; however, institutional barriers exist in the United States that severely limit their adaptive capacities (very high confidence). These barriers include limited access to traditional territory and resources and the limitations of existing policies, programs, and funding mechanisms in accounting for the unique conditions of Indigenous communities. Successful adaptation in Indigenous contexts relies on use of Indigenous knowledge, resilient and robust social systems and protocols, a commitment to principles of self-determination, and proactive efforts on the part of federal, state, and local governments to alleviate institutional barriers (high confidence).
' uncertainties: 'Adaptation is still in its infancy in most Indigenous (and non-Indigenous) communities in the United States, so there have not been enough projects implemented all the way to completion to be able to observe results and draw conclusions regarding the efficacy of any particular adaptation process or approach. Extrapolations can be made, however, from other relevant and closely related environmental decision-making processes, such as for land or water resource management.
' uri: /report/nca4/chapter/tribal-and-indigenous-communities/finding/key-message-15-3 url: ~ - chapter_identifier: north-american-and-other-international-effects confidence: "The portion of the main message pertaining to the future is very likely due to the likelihood of future climate change{{< tbib '3' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and persistence of the sensitivity of the U.S. economy and its trade to climate conditions. There is medium confidence that climate change and extremes outside the United States are impacting and will increasingly impact our trade and economy because there is insufficient empirical analysis on the causal relationships between past international climate variations outside the United States and U.S. economics and trade to provide higher confidence at this time. No attempt was made in this chapter to define the net impact of international climate change on the U.S. economy and trade; such a statement would have had very low confidence due to the current paucity of quantitative analyses.
" evidence: "Major U.S. firms are concerned about potential climate change impacts to their business (e.g., Peace et al. 2013, Peace and Maher 2015{{< tbib '10' '274b75cc-ce53-436a-b971-99fe1d9b371f' >}},{{
The Fourth National Climate Assessment (NCA4) is the first U.S. National Climate Assessment (NCA) to include a chapter that addresses the impacts of climate change beyond the borders of the United States. This chapter was included in NCA4 in response to comments received during public review of the Third National Climate Assessment (NCA3) that proposed that future NCAs include an analysis of international impacts of climate change as they relate to U.S. interests.
This chapter focuses on the implications of international impacts of climate change on U.S. interests. It does not address or summarize all international impacts of climate change; that very broad topic is covered by Working Group II of the Intergovernmental Panel on Climate Change (IPCC; e.g., IPCC 2014{{< tbib '1' 'c390e13f-8517-40a9-a236-ac4dede3a7a0' >}}). The U.S. government supports and participates in the IPCC process. The more focused topic of how U.S. interests can be affected by climate impacts outside of the United States is not specifically addressed by the IPCC.
The topics in the chapter—economics and trade, international development and humanitarian assistance, national security, and transboundary resources—were selected because they illustrate ways in which U.S. interests can be affected by international climate impacts. These topics cut across the world, so the chapter does not focus on impacts in specific regions.
The transboundary section was added to address climate-related impacts across U.S. borders. While the regional chapters address local and regional transboundary impacts, they do not address impacts that exist in multiple regions or agreements between the United States and its neighbors that create mechanisms for addressing such impacts.
The science section is part of the chapter because of the importance of international scientific cooperation to our understanding of climate science. That topic is not treated as a separate section because it is not a risk-based issue and therefore not an appropriate candidate to have as a Key Message.
The U.S. Global Change Research Program (USGCRP) put out a call for authors for the International chapter both inside and outside the Federal Government. The USGCRP asked for nominations of and by individuals with experience and knowledge on international climate change impacts and implications for the United States as well as experience in assessments such as the NCA.
All of the authors selected for the chapter have extensive experience in international climate change, and several had been authors on past NCAs. Section lead assignments were made based on the expertise of the individuals and, for those authors who are current federal employees, based on the expertise of the agencies. The author team of ten individuals is evenly divided between federal and non-federal personnel.
The coordinating lead author (CLA) and USGCRP organized two public outreach meetings. The first meeting was held at the Wilson Center in Washington, DC, on September 15, 2016, as part of the U.S. Agency for International Development’s (USAID) Adaptation Community Meetings and solicited input on the outline of the chapter and asked for volunteers to become chapter authors or otherwise contribute to the chapter. A public review meeting regarding the International chapter was held on April 6, 2017, at Chemonics in Washington, DC, also as part of USAID’s Adaptation Community Meetings series. The USGCRP and chapter authors shared information about the progress to date of the International chapter and sought input from stakeholders to help inform further development of the chapter, as well as to raise general awareness of the process and timeline for NCA4.
The chapter was revised in response to comments from the public and from the National Academy of Sciences. The comments were reviewed and discussed by the entire author team and the review editor, Dr. Diana Liverman of the University of Arizona. Individual authors drafted responses to comments on their sections, while the CLA and the chapter lead (CL) drafted responses to comments that pertained to the entire chapter. All comments were reviewed by the CLA and CL. The review editor reviewed responses to comments and revisions to the chapter to ensure that all comments had been considered by the authors.
" report_identifier: nca4 statement: 'The impacts of climate change, variability, and extreme events outside the United States are affecting and are virtually certain to increasingly affect U.S. trade and economy, including import and export prices and businesses with overseas operations and supply chains (very likely, medium confidence).
' uncertainties: 'The literature base on the impacts of climate change outside U.S. borders to the U.S. economy and trade is significantly smaller than that on climate change impacts within U.S. borders. In particular, few studies have attempted to quantify the magnitude of the past impacts of climate variability and change that occur outside the United States on U.S. economics and trade. Since there is limited literature, it is unclear how climate-driven regional shifts in economic activity will affect U.S. economics and trade. Nonetheless, the general nature of the main types of impacts described in this section are relatively well known.
' uri: /report/nca4/chapter/north-american-and-other-international-effects/finding/key-message-16-1 url: ~ - chapter_identifier: north-american-and-other-international-effects confidence: 'There is high confidence in the Key Message. There is ample evidence that the impacts of climate variability and change negatively affect the economies and societies of developing countries and set back development efforts. There is also evidence of these impacts leading to additional U.S. interventions, whether through humanitarian or other means, in some places.
' evidence: "The link between climate variability, natural disasters, and socioeconomic development is fairly well established (e.g., UNISDR 2015, Hallegatte et al. 2017{{< tbib '149' '06cddfdc-2771-4803-98cf-31136413ac1f' >}},{{
The relationship between climate change and socioeconomic development has been assessed extensively by the Intergovernmental Panel on Climate Change through its assessment reports (e.g., IPCC 2014{{< tbib '1' 'c390e13f-8517-40a9-a236-ac4dede3a7a0' >}}). There is some research on the economic costs and benefits from climate change (e.g., Nordhaus 1994, Stern et al. 2006, Estrada et al. 2017, Tol 2018{{< tbib '153' '67a3627d-c737-41bf-b6cb-f730ce3dfd58' >}},{{
The United States has long invested in socioeconomic development in poorer countries with the intention of reducing poverty and encouraging stability. Additionally, stable and prosperous countries make for potential trading partners and a reduced risk of conflict. These ideas are presented in numerous U.S. development, diplomacy, and security strategies (e.g., U.S. Department of State and USAID 2018, 2015{{< tbib '40' 'b77adb22-aea6-4397-9dab-0a67ee992606' >}},{{
The Fourth National Climate Assessment (NCA4) is the first U.S. National Climate Assessment (NCA) to include a chapter that addresses the impacts of climate change beyond the borders of the United States. This chapter was included in NCA4 in response to comments received during public review of the Third National Climate Assessment (NCA3) that proposed that future NCAs include an analysis of international impacts of climate change as they relate to U.S. interests.
This chapter focuses on the implications of international impacts of climate change on U.S. interests. It does not address or summarize all international impacts of climate change; that very broad topic is covered by Working Group II of the Intergovernmental Panel on Climate Change (IPCC; e.g., IPCC 2014{{< tbib '1' 'c390e13f-8517-40a9-a236-ac4dede3a7a0' >}}). The U.S. government supports and participates in the IPCC process. The more focused topic of how U.S. interests can be affected by climate impacts outside of the United States is not specifically addressed by the IPCC.
The topics in the chapter—economics and trade, international development and humanitarian assistance, national security, and transboundary resources—were selected because they illustrate ways in which U.S. interests can be affected by international climate impacts. These topics cut across the world, so the chapter does not focus on impacts in specific regions.
The transboundary section was added to address climate-related impacts across U.S. borders. While the regional chapters address local and regional transboundary impacts, they do not address impacts that exist in multiple regions or agreements between the United States and its neighbors that create mechanisms for addressing such impacts.
The science section is part of the chapter because of the importance of international scientific cooperation to our understanding of climate science. That topic is not treated as a separate section because it is not a risk-based issue and therefore not an appropriate candidate to have as a Key Message.
The U.S. Global Change Research Program (USGCRP) put out a call for authors for the International chapter both inside and outside the Federal Government. The USGCRP asked for nominations of and by individuals with experience and knowledge on international climate change impacts and implications for the United States as well as experience in assessments such as the NCA.
All of the authors selected for the chapter have extensive experience in international climate change, and several had been authors on past NCAs. Section lead assignments were made based on the expertise of the individuals and, for those authors who are current federal employees, based on the expertise of the agencies. The author team of ten individuals is evenly divided between federal and non-federal personnel.
The coordinating lead author (CLA) and USGCRP organized two public outreach meetings. The first meeting was held at the Wilson Center in Washington, DC, on September 15, 2016, as part of the U.S. Agency for International Development’s (USAID) Adaptation Community Meetings and solicited input on the outline of the chapter and asked for volunteers to become chapter authors or otherwise contribute to the chapter. A public review meeting regarding the International chapter was held on April 6, 2017, at Chemonics in Washington, DC, also as part of USAID’s Adaptation Community Meetings series. The USGCRP and chapter authors shared information about the progress to date of the International chapter and sought input from stakeholders to help inform further development of the chapter, as well as to raise general awareness of the process and timeline for NCA4.
The chapter was revised in response to comments from the public and from the National Academy of Sciences. The comments were reviewed and discussed by the entire author team and the review editor, Dr. Diana Liverman of the University of Arizona. Individual authors drafted responses to comments on their sections, while the CLA and the chapter lead (CL) drafted responses to comments that pertained to the entire chapter. All comments were reviewed by the CLA and CL. The review editor reviewed responses to comments and revisions to the chapter to ensure that all comments had been considered by the authors.
" report_identifier: nca4 statement: 'The impacts of climate change, variability, and extreme events can slow or reverse social and economic progress in developing countries, thus undermining international aid and investments made by the United States and increasing the need for humanitarian assistance and disaster relief (likely, high confidence). The United States provides technical and financial support to help developing countries better anticipate and address the impacts of climate change, variability, and extreme events.
' uncertainties: "Climate change adaptation is an emerging field, and most adaptation work is being carried out by governments, local communities, and development practitioners through support from development agencies and multilateral institutions. Evaluations of the effectiveness of adaptation interventions are generally conducted at the project level for its funder, and results may not be publicized. Some research is emerging on the economic benefits of adaptation interventions (e.g., Hallegatte et al. 2016, Chambwera et al. 2014{{< tbib '158' '310326ad-14fc-408e-aaf8-61a4e44e33fc' >}},{{
There is consensus on framing climate as a stressor on other factors contributing to national security. Given the knowledge of factors that increase the risk of civil wars, and evidence that some of these factors are sensitive to climate change, the IPCC found justifiable concern that “climate change or changes in climate variability [could] increase the risk of armed conflict in certain circumstances.”{{< tbib '61' 'd5216e42-45ce-457b-bda8-b2e445d23c0d' >}} However, the literature examining specific causality does not result in a high confidence conclusion to link climate and conflict, which is reflected in the Key Message medium confidence assignment. Multiple schools of thought exist on the mechanisms and degree of linkages, and models are incomplete. Data are improving and evidence continues to emerge, but the inconsistent evidence limits our ability to assign a probability to this Key Message.
Nonetheless, with regard to climate impacts on physical infrastructure, the DoD observes changes in the infrastructure at its installations that are consistent with climate change. In keeping with sound stewardship and prudence, it uses scenario-driven approaches to identify areas of risk while continuing to research and provide resilient responses to the observed changes.
" evidence: "Based on an assessment of a wide range of scientific literature on climate and security, multiple national security reports have framed climate change as a stressor on national security.{{< tbib '59' 'b00dec8c-2a2a-415d-a951-58304a00fc62' >}},{{
The U.S. military is observing climate change impacts to its infrastructure and is taking a scenario-driven, risk-based approach to address resultant challenges. Exceedance probability plots of the type used to support engineering siting and design analysis were used but modified to include responses to time-specific tidal phases and historical trends to create an estimate of the “present day” exceedance probability. The hindcast projections kept pace with an Intermediate-Low sea level rise scenario of approximately 5 mm/year (about 0.2 inches/year).{{< tbib '171' 'af1f3f53-c612-4dcb-9c28-31c859d5a03e' >}} The focus for Department of Defense (DoD) infrastructure management, however, is the resultant increased trend for exceedances that would challenge infrastructure functional integrity (such as negative impacts to critical roadways and airfields).{{< tbib '171' 'af1f3f53-c612-4dcb-9c28-31c859d5a03e' >}} In an effort to understand risks to the integrity of coastal facilities more broadly, the DoD uses a scenario-driven risk management approach to support decision-making regarding its coastal installations and facilities. The scenario approaches provide a framework for the inherent uncertainties of future events while providing decision support. Scenarios are not simply predictions about the future but rather plausible futures bounded by observations and the constraints of physics. Using scenarios, decision-makers can then examine risks through the lens of event impacts, costs of additional analysis, and the results of inaction. In this way, inaction is recognized as an important decision in its own right.{{< tbib '64' 'd2dc9855-41bc-4e94-bb79-f0ba2ff2684b' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/north-american-and-other-international-effects/finding/key-message-16-3.yaml identifier: key-message-16-3 ordinal: 3 process: "The Fourth National Climate Assessment (NCA4) is the first U.S. National Climate Assessment (NCA) to include a chapter that addresses the impacts of climate change beyond the borders of the United States. This chapter was included in NCA4 in response to comments received during public review of the Third National Climate Assessment (NCA3) that proposed that future NCAs include an analysis of international impacts of climate change as they relate to U.S. interests.
This chapter focuses on the implications of international impacts of climate change on U.S. interests. It does not address or summarize all international impacts of climate change; that very broad topic is covered by Working Group II of the Intergovernmental Panel on Climate Change (IPCC; e.g., IPCC 2014{{< tbib '1' 'c390e13f-8517-40a9-a236-ac4dede3a7a0' >}}). The U.S. government supports and participates in the IPCC process. The more focused topic of how U.S. interests can be affected by climate impacts outside of the United States is not specifically addressed by the IPCC.
The topics in the chapter—economics and trade, international development and humanitarian assistance, national security, and transboundary resources—were selected because they illustrate ways in which U.S. interests can be affected by international climate impacts. These topics cut across the world, so the chapter does not focus on impacts in specific regions.
The transboundary section was added to address climate-related impacts across U.S. borders. While the regional chapters address local and regional transboundary impacts, they do not address impacts that exist in multiple regions or agreements between the United States and its neighbors that create mechanisms for addressing such impacts.
The science section is part of the chapter because of the importance of international scientific cooperation to our understanding of climate science. That topic is not treated as a separate section because it is not a risk-based issue and therefore not an appropriate candidate to have as a Key Message.
The U.S. Global Change Research Program (USGCRP) put out a call for authors for the International chapter both inside and outside the Federal Government. The USGCRP asked for nominations of and by individuals with experience and knowledge on international climate change impacts and implications for the United States as well as experience in assessments such as the NCA.
All of the authors selected for the chapter have extensive experience in international climate change, and several had been authors on past NCAs. Section lead assignments were made based on the expertise of the individuals and, for those authors who are current federal employees, based on the expertise of the agencies. The author team of ten individuals is evenly divided between federal and non-federal personnel.
The coordinating lead author (CLA) and USGCRP organized two public outreach meetings. The first meeting was held at the Wilson Center in Washington, DC, on September 15, 2016, as part of the U.S. Agency for International Development’s (USAID) Adaptation Community Meetings and solicited input on the outline of the chapter and asked for volunteers to become chapter authors or otherwise contribute to the chapter. A public review meeting regarding the International chapter was held on April 6, 2017, at Chemonics in Washington, DC, also as part of USAID’s Adaptation Community Meetings series. The USGCRP and chapter authors shared information about the progress to date of the International chapter and sought input from stakeholders to help inform further development of the chapter, as well as to raise general awareness of the process and timeline for NCA4.
The chapter was revised in response to comments from the public and from the National Academy of Sciences. The comments were reviewed and discussed by the entire author team and the review editor, Dr. Diana Liverman of the University of Arizona. Individual authors drafted responses to comments on their sections, while the CLA and the chapter lead (CL) drafted responses to comments that pertained to the entire chapter. All comments were reviewed by the CLA and CL. The review editor reviewed responses to comments and revisions to the chapter to ensure that all comments had been considered by the authors.
" report_identifier: nca4 statement: 'Climate change, variability, and extreme events, in conjunction with other factors, can exacerbate conflict, which has implications for U.S. national security (medium confidence). Climate impacts already affect U.S. military infrastructure, and the U.S. military is incorporating climate risks in its planning (high confidence).
' uncertainties: "The impact and risk of conflict related to climate change is difficult to separate from other drivers of environmental vulnerability, including economic activity, education, health, and food security.{{< tbib '61' 'd5216e42-45ce-457b-bda8-b2e445d23c0d' >}},{{
Datasets on climate change, conflict, and security are often limited in length and pose statistical difficulties.{{< tbib '70' '32ad430a-4769-4e16-8ece-c28d123504b0' >}} However, recent advances in statistical analysis have begun to allow the quantification of indirect effects of multiple variables connecting climatic pressures and violence.{{< tbib '172' 'fef51b51-9036-4b22-98ba-94d9159a2514' >}} These results are preliminary, mostly due to a lack of necessary data and the difficulty of quantifying relevant social variables, such as identity politics or grievances. There is a widespread pattern of examining instances of conflict for drivers, precluding the possibility of finding that climate-related stressors did not result in conflict. There is a need to analyze situations where no conflict occurred despite existing climate risks. Intercomparison of quantitative studies of the link between conflict and adverse climate conditions is complicated because the wide range of climatic and social indicators differ in spatial and temporal coverage, often due to a lack of data availability. Prehistoric and premodern evidence of the impact of climate change on conflict is not necessarily relevant to modern societies,{{< tbib '167' '069f4158-18f0-475d-a33e-8b21a935be8c' >}} and some of the climate shifts currently being faced are unprecedented over centuries to millennia.{{< tbib '170' 'e4456b15-44b5-45d0-a92d-36f7be665121' >}} Therefore, the possible existence of a relationship is better understood than its particulars and is best expressed in the formulation that climate extremes and change can exacerbate conflict.
The ongoing Syrian conflict is often framed in terms of climate change. However, it is not possible to draw conclusions on the role of climate in the outcome of an ongoing conflict. Moreover, the role of climate variability (such as drought), the contribution of climate change to such variability, and the contribution of climate variability to the subsequent conflict is a matter of active debate in the assessed literature.{{< tbib '173' 'cb442681-f8b0-4d84-821e-402ce5367991' >}},{{
The documented impacts of climate on national security largely occur through processes associated with natural climate variability, such as drought, El Niño, and tropical storms. While observed and projected increases in extreme weather and climate events have been attributed to climate change, uncertainty remains.{{< tbib '48' 'a29b612b-8c28-4c93-9c18-19314babce89' >}},{{
Similarly, additional studies are underway to determine the potential impacts of climate change on DoD resources and mission capabilities. Many of these efforts seek to assess the vulnerability of infrastructure to climate change across a wide variety of ecosystems.{{< tbib '180' 'cf17e1a8-88d4-4e55-ba9f-6a6ce1c1d2ab' >}},{{
There is high confidence in the main message. There is sufficient empirical analysis on the relationships between past climate variations along U.S. international borders. The statement about the likelihood that impacts on shared resources will affect the bilateral frameworks established to manage these resources is based on expert understanding of the integration of climate risk into existing and future frameworks.
' evidence: "In the U.S.–Mexico drylands region, large areas are projected to become drier,{{< tbib '102' '37d85f6f-8d91-45e8-bf65-0ae8aee523a6' >}} which will present increasing demands for water resources on top of existing stresses related to population growth.{{< tbib '103' 'c9075dbc-f7c8-4d85-b534-e97282562b3e' >}},{{
The Fourth National Climate Assessment (NCA4) is the first U.S. National Climate Assessment (NCA) to include a chapter that addresses the impacts of climate change beyond the borders of the United States. This chapter was included in NCA4 in response to comments received during public review of the Third National Climate Assessment (NCA3) that proposed that future NCAs include an analysis of international impacts of climate change as they relate to U.S. interests.
This chapter focuses on the implications of international impacts of climate change on U.S. interests. It does not address or summarize all international impacts of climate change; that very broad topic is covered by Working Group II of the Intergovernmental Panel on Climate Change (IPCC; e.g., IPCC 2014{{< tbib '1' 'c390e13f-8517-40a9-a236-ac4dede3a7a0' >}}). The U.S. government supports and participates in the IPCC process. The more focused topic of how U.S. interests can be affected by climate impacts outside of the United States is not specifically addressed by the IPCC.
The topics in the chapter—economics and trade, international development and humanitarian assistance, national security, and transboundary resources—were selected because they illustrate ways in which U.S. interests can be affected by international climate impacts. These topics cut across the world, so the chapter does not focus on impacts in specific regions.
The transboundary section was added to address climate-related impacts across U.S. borders. While the regional chapters address local and regional transboundary impacts, they do not address impacts that exist in multiple regions or agreements between the United States and its neighbors that create mechanisms for addressing such impacts.
The science section is part of the chapter because of the importance of international scientific cooperation to our understanding of climate science. That topic is not treated as a separate section because it is not a risk-based issue and therefore not an appropriate candidate to have as a Key Message.
The U.S. Global Change Research Program (USGCRP) put out a call for authors for the International chapter both inside and outside the Federal Government. The USGCRP asked for nominations of and by individuals with experience and knowledge on international climate change impacts and implications for the United States as well as experience in assessments such as the NCA.
All of the authors selected for the chapter have extensive experience in international climate change, and several had been authors on past NCAs. Section lead assignments were made based on the expertise of the individuals and, for those authors who are current federal employees, based on the expertise of the agencies. The author team of ten individuals is evenly divided between federal and non-federal personnel.
The coordinating lead author (CLA) and USGCRP organized two public outreach meetings. The first meeting was held at the Wilson Center in Washington, DC, on September 15, 2016, as part of the U.S. Agency for International Development’s (USAID) Adaptation Community Meetings and solicited input on the outline of the chapter and asked for volunteers to become chapter authors or otherwise contribute to the chapter. A public review meeting regarding the International chapter was held on April 6, 2017, at Chemonics in Washington, DC, also as part of USAID’s Adaptation Community Meetings series. The USGCRP and chapter authors shared information about the progress to date of the International chapter and sought input from stakeholders to help inform further development of the chapter, as well as to raise general awareness of the process and timeline for NCA4.
The chapter was revised in response to comments from the public and from the National Academy of Sciences. The comments were reviewed and discussed by the entire author team and the review editor, Dr. Diana Liverman of the University of Arizona. Individual authors drafted responses to comments on their sections, while the CLA and the chapter lead (CL) drafted responses to comments that pertained to the entire chapter. All comments were reviewed by the CLA and CL. The review editor reviewed responses to comments and revisions to the chapter to ensure that all comments had been considered by the authors.
" report_identifier: nca4 statement: 'Shared resources along U.S. land and maritime borders provide direct benefits to Americans and are vulnerable to impacts from a changing climate, variability, and extremes (very likely, high confidence). Multinational frameworks that manage shared resources are increasingly incorporating climate risk in their transboundary decision-making processes.
' uncertainties: "Impacts on shared resources along U.S. international borders are already being experienced. Uncertainties about the impacts are aligned with the uncertainties associated with projections of future climate variability. As elaborated upon in multiple regional chapters of this report (Ch. 18: Northeast; Ch. 20: U.S. Caribbean; Ch. 21: Midwest; Ch. 24: Northwest; Ch. 25: Southwest; Ch. 26: Alaska; Ch. 27: Hawai‘i & Pacific Islands), weather patterns in these border regions are projected to continue to change with varying degrees of likelihood and confidence.
" uri: /report/nca4/chapter/north-american-and-other-international-effects/finding/key-message-16-4 url: ~ - chapter_identifier: sectoral-interdependencies-and-compounding-stressors confidence: 'We have high confidence in this message, because there is high agreement and extensive evidence that a range of critical intersectoral interdependencies and compounding stressors are present and relevant to climate risk assessment. At the same time, the precise impact of these on system dynamics is not well understood.
' evidence: "A suite of examples across this assessment and within this chapter demonstrate the interactions between systems and the potentially important implications of these linkages. Examples in this chapter include Hurricane Harvey; the 2003 Northeast blackout; energy–water–land systems in California and throughout the nation; forest systems facing influences from wildfires, drought, and pine bark beetles; and the implications of the reintroduction of wolves in Yellowstone. Each of these examples is supported by its own evidence base; the linkages between systems and the importance of non-climate influences is self-evident from these examples. Beyond these examples, a small set of recent literature has begun to explore ways to more systematically quantify the implications of including sectoral interdependencies in climate risk assessment (e.g., Harrison et al. 2016{{< tbib '8' '2a131189-94cc-4c86-bb51-2fc0bf6a4504' >}}).
In addition to literature specific to risk assessment in the context of climate change, there is a long history of research on complex systems{{< tbib '11' '87e9e534-034f-450c-b205-f268be5c2152' >}} that raises the potential for a range of dynamics that might emerge from sectoral interdependencies and compounding stressors. This includes research spanning disciplines from meteorology{{< tbib '12' 'ff6f1e9a-1875-438b-b628-c107c5de2396' >}} to ecology{{< tbib '13' 'ceb49ae3-99c4-4009-a382-c3f26891e687' >}} to paleontology{{< tbib '14' '82abbb5d-1c8e-4178-82c3-249fb0fdf168' >}} to computer science.{{< tbib '15' 'a4feb2d0-0a82-4f20-98af-89c295b177c0' >}} This literature supports the conclusion that more complex dynamics may occur when multiple systems interact with one another.
" href: https://data.globalchange.gov/report/nca4/chapter/sectoral-interdependencies-and-compounding-stressors/finding/key-message-17-1.yaml identifier: key-message-17-1 ordinal: 1 process: 'The scope of this chapter was developed to fill a gap in previous National Climate Assessments (NCAs), notably the risks that emerge from interactions among sectors. Previous NCAs have touched on this subject, for example the energy, water, and land use chapter in the Third National Climate Assessment (NCA3). However, these assessments never included a chapter specifically focused on a general treatment of this topic. Emerging scientific research is highlighting the links between sectors and the potential complexity and implications of these interactions, from complex system dynamics such as cascading failures to management approaches and approaches to risk. These concepts were then incorporated into a detailed terms of reference for the chapter, outlining the scope and the general content to be included in the document.
The author team for this chapter was constructed to bring together the necessary diverse experience, expertise, and perspectives. Our authors brought expertise and experience in multiscale, multisector research and modeling, with a focus in specific sectors or sectoral combinations including critical infrastructure, energy–water–land interactions, and ecosystems. The authors also had expertise in complex systems science and previous experience in assessment processes.
The chapter was developed through technical discussions, a literature review, and expert deliberation by chapter authors through email and phone discussions. The team evaluated the state of the science on the analysis of sectoral interdependencies, compounding stressors, and complex system science. Case studies were drawn from a range of sources intended to represent the key themes in the chapter.
' report_identifier: nca4 statement: 'The sectors and systems exposed to climate (for example, energy, water, and agriculture) interact with and depend on one another and other systems less directly exposed to climate (such as the financial sector). In addition, these interacting systems are not only exposed to climate-related stressors such as floods, droughts, and heat waves, they are also subject to a range of non-climate factors, from population movements to economic fluctuations to urban expansion. These interactions can lead to complex behaviors and outcomes that are difficult to predict. It is not possible to fully understand the implications of climate change on the United States without considering the interactions among sectors and their consequences. (High Confidence)
' uncertainties: 'The interactions between sectors and systems relevant to climate risk assessment are self-evident, and there are clear examples of unanticipated dynamics emerging from these interactions in the past. Yet our understanding is limited regarding the precise nature of complex system behavior in the context of climate risk assessment and its ultimate influence on the outcomes of such assessments. As noted in Key Message 4, the available tools and frameworks are simply not sufficient at this point to identify key risks emerging from intersectoral interdependencies and compounding stressors.
' uri: /report/nca4/chapter/sectoral-interdependencies-and-compounding-stressors/finding/key-message-17-1 url: ~ - chapter_identifier: sectoral-interdependencies-and-compounding-stressors confidence: 'We have high confidence in this Key Message because there is high agreement that a multisector perspective alters risk assessment, as is reflected in recent climate change assessments. However, the evidence basis for multisector evaluations is emerging.
' evidence: "Recent climate change assessments (e.g., Oppenheimer et al. 2014, Houser et al. 2015{{< tbib '45' '0ea6d723-5df9-4b45-8d5f-be269119ccf8' >}},{{
Different tools and approaches are required to assess multisector risks. Approaches can be applied to integrate diverse evidence, combining quantitative and qualitative results and drawing from the natural and social sciences and other forms of analysis.{{< tbib '47' '0bf999f3-8291-493a-bf19-525a26af5125' >}},{{
The scope of this chapter was developed to fill a gap in previous National Climate Assessments (NCAs), notably the risks that emerge from interactions among sectors. Previous NCAs have touched on this subject, for example the energy, water, and land use chapter in the Third National Climate Assessment (NCA3). However, these assessments never included a chapter specifically focused on a general treatment of this topic. Emerging scientific research is highlighting the links between sectors and the potential complexity and implications of these interactions, from complex system dynamics such as cascading failures to management approaches and approaches to risk. These concepts were then incorporated into a detailed terms of reference for the chapter, outlining the scope and the general content to be included in the document.
The author team for this chapter was constructed to bring together the necessary diverse experience, expertise, and perspectives. Our authors brought expertise and experience in multiscale, multisector research and modeling, with a focus in specific sectors or sectoral combinations including critical infrastructure, energy–water–land interactions, and ecosystems. The authors also had expertise in complex systems science and previous experience in assessment processes.
The chapter was developed through technical discussions, a literature review, and expert deliberation by chapter authors through email and phone discussions. The team evaluated the state of the science on the analysis of sectoral interdependencies, compounding stressors, and complex system science. Case studies were drawn from a range of sources intended to represent the key themes in the chapter.
' report_identifier: nca4 statement: 'Climate change risk assessment benefits from a multisector perspective, encompassing interactions among sectors and both climate and non-climate stressors. Because such interactions and their consequences can be challenging to identify in advance, effectively assessing multisector risks requires tools and approaches that integrate diverse evidence and that consider a wide range of possible outcomes. (High Confidence)
' uncertainties: 'For interdependent systems affected by multiple stressors, the number and complexity of possible interactions are greater, presenting deeper uncertainties. It is often difficult or impossible to represent all relevant processes and interactions in analyses of risks, especially quantitatively. For example, quantitative projections can evaluate probabilities of well-understood sectoral interactions but will be limited by processes or parameters that are poorly known or unknowable. This is why the integration of diverse evidence and attention to deeper uncertainties are important in multisector risk assessment.
' uri: /report/nca4/chapter/sectoral-interdependencies-and-compounding-stressors/finding/key-message-17-2 url: ~ - chapter_identifier: sectoral-interdependencies-and-compounding-stressors confidence: 'There is high agreement and extensive evidence that institutional arrangements and governance are critical to the management of systems and their interdependencies. This finding is reflected in scientific assessments, modeling studies, and observations of system responses and performance, as well as in theories emerging from complex systems science. Furthermore, a history of management practice associated with water, energy, transportation, telecommunications, food, and health systems that spans decades to centuries provides evidence for the importance of system interdependencies. Thus, there is high Confidence in this message.
' evidence: "Recent literature has documented that the management of interacting infrastructure systems is a key factor influencing their resilience to climate and other stressors. A range of studies have argued that the complexity of institutional arrangements in mature, democratic economies like the United States poses challenges to the pursuit of climate adaptation objectives and sustainability more broadly.{{< tbib '72' '747e6b30-6afc-4520-af4b-660389e167ba' >}},{{
The interdependencies among systems reflect the potential value in the development of more integrated management strategies.{{< tbib '72' '747e6b30-6afc-4520-af4b-660389e167ba' >}} This concept of integrated management is reflected in existing literatures, particularly those associated with integrated water resources management {{< tbib '106' 'f43680e8-feb9-4e43-aaa3-26b843935b35' >}},{{
A range of strategies have been proposed for enhancing the capacity to manage system interdependencies and climate change risk. Significant effort has been invested in understanding and modeling system dynamics to enhance capabilities for risk and vulnerability assessment. These efforts have largely focused on physical infrastructure systems, infrastructure networks, and the potential for cascading failures.{{< tbib '116' 'd5343adc-cad7-4ec5-89db-02b4e7432c1a' >}},{{
There is ample evidence of comanagement of interdependent systems, often as a function of resource assurance and/or contingency planning. For example, the use of water for electricity generation (hydropower or cooling in thermal generation) involves regulatory constraints around water use as well as operational decision-making regarding water management.{{< tbib '72' '747e6b30-6afc-4520-af4b-660389e167ba' >}},{{
A key element of such planning is to build redundancy and flexibility into system operations.{{< tbib '73' 'e70ad283-4e8b-4a9e-8279-6f7f830f98f5' >}} Evidence suggests that adding flexibility or robustness to systems or transforming systems such that they interact or behave in fundamentally different ways can increase construction, maintenance, or procurement costs.{{< tbib '82' '9a6c7a87-5c0f-4d64-904c-c707f68f2115' >}},{{
Given the complexity of governance systems, the responsibility for the design and implementation of such strategies for integrated management rests on a broad range of actors. Over the latter part of the 20th century, the privatization of infrastructure, including energy, telecommunications, and water, transferred infrastructure management, responsibility, and risk to the private sector.{{< tbib '135' '18325d52-df0d-4729-9e02-c0b0e8945fef' >}} Nevertheless, local, state, and federal governments continue to have critical roles in regulation, risk assessment, and research and development. In addition, many institutions, organizations, and individuals either have infrastructure dependencies or influence the dynamics, operations, investment, and performance of infrastructure.{{< tbib '136' '57da6191-41b4-48a5-8fe6-0d55fd26a01b' >}} The increasing interconnectedness of both infrastructure and the people who use and manage that infrastructure is leading to both new challenges and opportunities for comanaging these systems, particularly in urban areas.{{< tbib '137' 'c75e24cb-498e-400b-8f25-a47526666cf5' >}},{{
The scope of this chapter was developed to fill a gap in previous National Climate Assessments (NCAs), notably the risks that emerge from interactions among sectors. Previous NCAs have touched on this subject, for example the energy, water, and land use chapter in the Third National Climate Assessment (NCA3). However, these assessments never included a chapter specifically focused on a general treatment of this topic. Emerging scientific research is highlighting the links between sectors and the potential complexity and implications of these interactions, from complex system dynamics such as cascading failures to management approaches and approaches to risk. These concepts were then incorporated into a detailed terms of reference for the chapter, outlining the scope and the general content to be included in the document.
The author team for this chapter was constructed to bring together the necessary diverse experience, expertise, and perspectives. Our authors brought expertise and experience in multiscale, multisector research and modeling, with a focus in specific sectors or sectoral combinations including critical infrastructure, energy–water–land interactions, and ecosystems. The authors also had expertise in complex systems science and previous experience in assessment processes.
The chapter was developed through technical discussions, a literature review, and expert deliberation by chapter authors through email and phone discussions. The team evaluated the state of the science on the analysis of sectoral interdependencies, compounding stressors, and complex system science. Case studies were drawn from a range of sources intended to represent the key themes in the chapter.
' report_identifier: nca4 statement: 'The joint management of interacting systems can enhance the resilience of communities, industries, and ecosystems to climate-related stressors. For example, during drought events, river operations can be managed to balance water demand for drinking water, navigation, and electricity production. Such integrated approaches can help avoid missed opportunities or unanticipated tradeoffs associated with the implementation of management responses to climate-related stressors. (High Confidence)
' uncertainties: 'The dominant uncertainties associated with the management of climate risks and system interdependencies include understanding indirect effects and feedbacks between systems, particularly with respect to predicting system responses. Technological change could have significant implications for the resilience, interconnectedness, and responses of systems to climate-related stressors and other disturbances. Such change could increase the complexity of integrated management with implications that could be positive or negative with respect to vulnerability. In addition, the future evolution of governance and regulatory dimensions of infrastructures systems, as well as consumer choices and behavior, are associated with irreducible uncertainty, largely because they involve choices yet to be made.
' uri: /report/nca4/chapter/sectoral-interdependencies-and-compounding-stressors/finding/key-message-17-3 url: ~ - chapter_identifier: sectoral-interdependencies-and-compounding-stressors confidence: 'See above. No likelihood statement is appropriate, and the high confidence is based on the authors’ assessment of the underlying literature and development of methods and modeling tools.
' evidence: 'This Key Message is based on an understanding of a range of analyses and modeling tools described throughout the chapter.
' href: https://data.globalchange.gov/report/nca4/chapter/sectoral-interdependencies-and-compounding-stressors/finding/key-message-17-4.yaml identifier: key-message-17-4 ordinal: 4 process: 'The scope of this chapter was developed to fill a gap in previous National Climate Assessments (NCAs), notably the risks that emerge from interactions among sectors. Previous NCAs have touched on this subject, for example the energy, water, and land use chapter in the Third National Climate Assessment (NCA3). However, these assessments never included a chapter specifically focused on a general treatment of this topic. Emerging scientific research is highlighting the links between sectors and the potential complexity and implications of these interactions, from complex system dynamics such as cascading failures to management approaches and approaches to risk. These concepts were then incorporated into a detailed terms of reference for the chapter, outlining the scope and the general content to be included in the document.
The author team for this chapter was constructed to bring together the necessary diverse experience, expertise, and perspectives. Our authors brought expertise and experience in multiscale, multisector research and modeling, with a focus in specific sectors or sectoral combinations including critical infrastructure, energy–water–land interactions, and ecosystems. The authors also had expertise in complex systems science and previous experience in assessment processes.
The chapter was developed through technical discussions, a literature review, and expert deliberation by chapter authors through email and phone discussions. The team evaluated the state of the science on the analysis of sectoral interdependencies, compounding stressors, and complex system science. Case studies were drawn from a range of sources intended to represent the key themes in the chapter.
' report_identifier: nca4 statement: 'Predicting the responses of complex, interdependent systems will depend on developing meaningful models of multiple, diverse systems, including human systems, and methods for characterizing uncertainty. (High Confidence)
' uncertainties: 'Because the Key Message is the authors’ assessment of the overall state of development of research tools and models, and the subsequent importance of developing research tools, the concept of major uncertainties is not entirely appropriate. This is a matter of the authors’ judgment, not calculation or assessment of underlying probabilities.
' uri: /report/nca4/chapter/sectoral-interdependencies-and-compounding-stressors/finding/key-message-17-4 url: ~ - chapter_identifier: northeast confidence: 'There is high confidence that the combined effects of increasing winter and early-spring temperatures and increasing winter precipitation (very high confidence) are changing aquatic and terrestrial habitats and affecting the species adapted to them. The impact of changing seasonal temperature, moisture conditions, and habitats will vary geographically and impact interactions among species. It is likely that some will not adapt. There is high confidence that over the next century, some species will decline while other species introduced to the region thrive as conditions change. There is high confidence that increased precipitation in early spring will negatively impact farming, but the response of vegetation to future changes in seasonal temperature and moisture conditions depends on plant hardiness for medium confidence in the level of risk to specialty crops and forestry. A reduction in the length of the snow season by mid-century is highly likely under lower and higher scenarios, with very high confidence that the winter recreation industry will be negatively impacted by the end of the century under lower and higher scenarios (RCP4.5 and RCP8.5).
' evidence: "Multiple lines of evidence show that changes in seasonal temperature and precipitation cycles have been observed in the Northeast.{{< tbib '3' '56148bf0-62f5-4ec7-8dbc-1e356e40bd42' >}},{{
These changes are affecting a number of plant and animal species throughout the region, including earlier bloom times and leaf-out,{{< tbib '71' '3307a62c-ed45-4399-bcb9-f77e71b1e626' >}},{{
Warmer winters will likely contribute to declining yields for specialty crops{{< tbib '35' 'b6e8b67c-7042-4b85-b432-033983875e14' >}} and fewer operational days for logging{{< tbib '88' '8a427d3d-8b74-4ed8-8ec0-530b4a2fcdc1' >}} and snow-dependent recreation.{{< tbib '115' 'bff3f502-9bc7-4d5f-859f-636a30c71624' >}},{{
It is understood that authors for a regional assessment must have scientific and regional credibility in the topical areas. Each author must also be willing and interested in serving in this capacity. Author selection for the Northeast chapter proceeded as follows:
First, the U.S. Global Change Research Program (USGCRP) released a Call for Public Nominations. Interested scientists were either nominated or self-nominated and their names placed into a database. The concurrent USGCRP Call for Public Nominations also solicited scientists to serve as chapter leads. Both lists were reviewed by the USGCRP with input from the coordinating lead author (CLA) and from the National Climate Assessment (NCA) Steering Committee. All regional chapter lead (CL) authors were selected by the USGCRP at the same time. The CLA and CL then convened to review the author nominations list as a “first cut” in identifying potential chapter authors for this chapter. Using their knowledge of the Northeast’s landscape and challenges, the CLA and CL used the list of national chapter topics that would be most relevant for the region. That topical list was associated with scientific expertise and a subset of the author list.
In the second phase, the CLA and CL used both the list of nominees as well as other scientists from around the region to build an author team that was representative of the Northeast’s geography, institutional affiliation (federal agencies and academic and research institutions), depth of subject matter expertise, and knowledge of selected regional topics. Eleven authors were thus identified by December 2016, and the twelfth author was invited in April 2017 to better represent tribal knowledge in the chapter.
Lastly, the authors were contacted by the CL to determine their level of interest and willingness to serve as experts on the region's topics of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues.
The first two drafts of the Northeast chapter were structured around the themes of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues. During the USGCRP-sponsored Regional Engagement Workshop held in Boston on February 10, 2017, feedback was solicited from approximately 150 online participants (comprising transportation officials, coastal managers, urban planners, city managers, fisheries managers, forest managers, state officials, and others) around the Northeast and other parts of the United States, on both the content of these topical areas and important focal areas for the region. Additional inputs were solicited from other in-person meetings such as the ICNet workshop and American Association of Geographers meetings, both held in April 2017. All feedback was then compiled with the lessons learned from the USGCRP CLA-CL meeting in Washington, DC, also held in April 2017. On April 28, 2017, the author team met in Burlington, Vermont, and reworked the chapter’s structure around the risk-based framing of interest to 1) changing seasonality, 2) coastal/ocean resources, 3) rural communities and livelihoods, 4) urban interconnectedness, and 5) adaptation.
" report_identifier: nca4 statement: 'The seasonality of the Northeast is central to the region’s sense of place and is an important driver of rural economies. Less distinct seasons with milder winter and earlier spring conditions (very high confidence) are already altering ecosystems and environments (high confidence) in ways that adversely impact tourism (very high confidence), farming (high confidence), and forestry (medium confidence). The region’s rural industries and livelihoods are at risk from further changes to forests, wildlife, snowpack, and streamflow (likely).
' uncertainties: "Warmer fall temperatures affect senescence, fruit ripening, migration, and hibernation, but are less well studied in the region{{< tbib '98' 'f773b2e9-428c-455b-82f9-a4dbf065d44b' >}} and must be considered alongside other climatic factors such as drought. Projections for summer rainfall in the Northeast are uncertain,{{< tbib '4' '4de020df-232e-45f8-8d44-f864565f0b84' >}} but evaporative demand for surface moisture is expected to increase with projected increases in summer temperatures.{{< tbib '3' '56148bf0-62f5-4ec7-8dbc-1e356e40bd42' >}},{{
Warming ocean temperatures (high confidence), acidification (high confidence), and sea level rise (very high confidence) will alter coastal and ocean ecosystems (likely) and threaten the ecosystems services provided by the coasts and oceans (likely) in the Northeast. There is high confidence that ocean temperatures have caused shifts in the distribution, productivity, and phenology of marine species and very high confidence that high tide flooding and storm surge impacts are being amplified by sea level rise. Because much will depend on how humans choose to address or adapt to these problems, and as there is considerable uncertainty over the extent to which many of these coastal systems will be able to adapt, there is medium confidence in the level of risk to traditions and livelihoods. It is likely that under higher scenarios, sea level rise will significantly alter the coastal landscape, and rising temperatures and acidification will affect marine populations and fisheries.
' evidence: "Warming rates on the Northeast Shelf have been higher than experienced in other ocean regions,{{< tbib '39' 'fb1f46cd-8b70-4a44-923a-66df61ffa0be' >}} and climate projections indicate that warming in this region will continue to exceed rates expected in other ocean regions.{{< tbib '48' 'f44f9474-6d98-43a9-8d7f-ee808ecaf41e' >}},{{
Research also shows that sea level rise has been{{< tbib '12' 'b58704d1-b4ec-46d0-9dd5-e7573523951e' >}},{{
It is understood that authors for a regional assessment must have scientific and regional credibility in the topical areas. Each author must also be willing and interested in serving in this capacity. Author selection for the Northeast chapter proceeded as follows:
First, the U.S. Global Change Research Program (USGCRP) released a Call for Public Nominations. Interested scientists were either nominated or self-nominated and their names placed into a database. The concurrent USGCRP Call for Public Nominations also solicited scientists to serve as chapter leads. Both lists were reviewed by the USGCRP with input from the coordinating lead author (CLA) and from the National Climate Assessment (NCA) Steering Committee. All regional chapter lead (CL) authors were selected by the USGCRP at the same time. The CLA and CL then convened to review the author nominations list as a “first cut” in identifying potential chapter authors for this chapter. Using their knowledge of the Northeast’s landscape and challenges, the CLA and CL used the list of national chapter topics that would be most relevant for the region. That topical list was associated with scientific expertise and a subset of the author list.
In the second phase, the CLA and CL used both the list of nominees as well as other scientists from around the region to build an author team that was representative of the Northeast’s geography, institutional affiliation (federal agencies and academic and research institutions), depth of subject matter expertise, and knowledge of selected regional topics. Eleven authors were thus identified by December 2016, and the twelfth author was invited in April 2017 to better represent tribal knowledge in the chapter.
Lastly, the authors were contacted by the CL to determine their level of interest and willingness to serve as experts on the region's topics of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues.
The first two drafts of the Northeast chapter were structured around the themes of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues. During the USGCRP-sponsored Regional Engagement Workshop held in Boston on February 10, 2017, feedback was solicited from approximately 150 online participants (comprising transportation officials, coastal managers, urban planners, city managers, fisheries managers, forest managers, state officials, and others) around the Northeast and other parts of the United States, on both the content of these topical areas and important focal areas for the region. Additional inputs were solicited from other in-person meetings such as the ICNet workshop and American Association of Geographers meetings, both held in April 2017. All feedback was then compiled with the lessons learned from the USGCRP CLA-CL meeting in Washington, DC, also held in April 2017. On April 28, 2017, the author team met in Burlington, Vermont, and reworked the chapter’s structure around the risk-based framing of interest to 1) changing seasonality, 2) coastal/ocean resources, 3) rural communities and livelihoods, 4) urban interconnectedness, and 5) adaptation.
" report_identifier: nca4 statement: 'The Northeast’s coast and ocean support commerce, tourism, and recreation that are important to the region’s economy and way of life. Warmer ocean temperatures, sea level rise, and ocean acidification (high confidence) threaten these services (likely). The adaptive capacity of marine ecosystems and coastal communities will influence ecological and socioeconomic outcomes as climate risks increase (high confidence).
' uncertainties: "Although work to value coastal and marine ecosystems services is still evolving,{{< tbib '6' '874f9406-dd99-4e92-b64a-4542c23d0d16' >}},{{
The Northeast Shelf is sensitive to ocean acidification, and many fisheries in the region are dependent on shell-forming organisms.{{< tbib '181' '07043123-9da3-43da-a9fa-36885cd77331' >}},{{
There is high confidence that weather-related impacts on urban centers already experienced today will become more common under a changing climate. For the Northeast, sea level rise is projected to occur at a faster rate than the global average, potentially increasing the impact of moderate and severe coastal flooding.{{< tbib '47' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}}
By the end of the century and under a higher scenario (RCP8.5), Coupled Model Intercomparison Project Phase 5 (CMIP5) models suggest that annual average temperatures will increase by more than 9°F (16°C) for much of the region (2071–2100 compared to 1976–2005), while precipitation is projected to increase, particularly during winter and spring.{{< tbib '50' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}}
Extreme events that impact urban environments have been observed to increase over much of the United States and are projected to continue to intensify. There is high confidence that heavy precipitation events have increased in intensity and frequency since 1901, with the largest increase in the Northeast, a trend projected to continue.{{< tbib '50' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} There is very high confidence that extreme heat events are increasing across most regions worldwide, a trend very likely to continue.{{< tbib '50' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} Extreme precipitation from tropical cyclones has not demonstrated a clear observed trend but is expected to increase in the future.{{< tbib '50' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}},{{
The urban built environment and related supply and management systems are at increased risk of disruption from a variety of increasing climate risks. These risks emerge from accelerated sea level rise as well as increased frequency of coastal and estuarine flooding, intense precipitation events, urban heating and heat waves, and drought.
Coastal flooding can lead to adverse health consequences, loss of life, and damaged property and infrastructure.{{< tbib '368' '641ac0a3-aad2-4422-a632-f07117fe694a' >}} Much of the region’s major industries and cities are located along the coast, with 88% of the region’s population and 68% of the regional gross domestic product.{{< tbib '260' '9f559c9b-c78e-4593-bcbe-f07661d29e16' >}} High tide flooding is also increasingly problematic and costly.{{< tbib '47' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} Rising sea level and amplified storm events can increase the magnitude and geographic size of a coastal flood event. The frequency of dangerous coastal flooding in the Northeast would more than triple with 2 feet of sea level rise.{{< tbib '93' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} In Boston, the areal extent of a 1% (1 in 100 chance of occurring in any given year) flood is expected to increase multifold in many coastal neighborhoods.{{< tbib '295' '4d61fbc8-2282-49e8-bb8c-e7d87075f424' >}} However, there will likely be notable variability across coastal locations. Using the 2014 U.S. National Climate Assessment’s Intermediate-High scenario for sea level rise (a global rise of 1.2 meters by 2100), the median number of flood events per year for the Northeast is projected to increase from 1 event per year experienced today to 5 events by 2030 and 25 events by 2045, with significant variation within the region.{{< tbib '410' '5f4de85b-be39-4ffd-ac94-1950932c0140' >}}
Intense precipitation events can lead to riverine and street-level flooding affecting urban environments. Over recent decades, the Northeast has experienced an increase of intense precipitation events, particularly in the spring and fall.{{< tbib '411' '9131626f-95e5-4b4c-8a4e-08183ff2fe12' >}} From 1958 to 2016, the number of heaviest 1% precipitation events (that is, an event that has a 1% chance of occurring in any given year) in the Northeast has increased by 55%.{{< tbib '58' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} A recent study suggests that this trend began rather abruptly after 1996, though uniformly across the region.{{< tbib '411' '9131626f-95e5-4b4c-8a4e-08183ff2fe12' >}}
Urban heating and heat waves threaten the health of the urban population and the integrity of the urban landscape. Due to the urban heat island effect, summer surface temperatures across Northeast cities were an average of 13°F to 16°F (7°C to 9°C) warmer than surrounding rural areas over a three-year period, 2003 to 2005.{{< tbib '412' '6b78125d-611b-402d-ab56-c409b15d52aa' >}} This is of concern, as rising temperatures increase heat- and pollution-related mortality while also stressing energy demands across the urban environment.{{< tbib '413' '5d45fe96-3a2f-4f4c-b989-406af17fc9af' >}} However, the degree of urban heat island intensity varies across cities depending on local factors such as whether the city is coastal or inland.{{< tbib '414' '8d5cd278-b5eb-4a23-aba3-79fc4b0f5544' >}} Recent analysis of mortality in major cities of the Northeast suggests that the region could experience an additional 2,300 deaths per year by 2090 from extreme heat under RCP8.5 (compared to an estimated 970 deaths per year under the lower scenario, RCP4.5) compared to 1989–2000.{{< tbib '29' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} Another study that considered 1,692 cities around the world suggested that without mitigation, total economic costs associated with climate change could be 2.6 times higher due to the warmer temperatures in urban versus extra-urban environments.{{< tbib '415' 'e904b5f2-2c5e-4e55-8365-2ba748291939' >}}
Changes in temperature and precipitation can have dramatic impacts on urban water supply available for municipal and industrial uses. Under a higher scenario (RCP8.5), the Northeast is projected to experience cumulative losses of $730 million (discounted at 3% in 2015 dollars) due to water supply shortfalls for the period 2015 to 2099.{{< tbib '29' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} Under a lower scenario (RCP4.5), the Northeast is projected to sustain losses of $510 million (discounted at 3% in 2015 dollars).{{< tbib '29' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} The losses are largely projected for the more southern and coastal areas in the region.
" href: https://data.globalchange.gov/report/nca4/chapter/northeast/finding/key-message-18-3.yaml identifier: key-message-18-3 ordinal: 3 process: "It is understood that authors for a regional assessment must have scientific and regional credibility in the topical areas. Each author must also be willing and interested in serving in this capacity. Author selection for the Northeast chapter proceeded as follows:
First, the U.S. Global Change Research Program (USGCRP) released a Call for Public Nominations. Interested scientists were either nominated or self-nominated and their names placed into a database. The concurrent USGCRP Call for Public Nominations also solicited scientists to serve as chapter leads. Both lists were reviewed by the USGCRP with input from the coordinating lead author (CLA) and from the National Climate Assessment (NCA) Steering Committee. All regional chapter lead (CL) authors were selected by the USGCRP at the same time. The CLA and CL then convened to review the author nominations list as a “first cut” in identifying potential chapter authors for this chapter. Using their knowledge of the Northeast’s landscape and challenges, the CLA and CL used the list of national chapter topics that would be most relevant for the region. That topical list was associated with scientific expertise and a subset of the author list.
In the second phase, the CLA and CL used both the list of nominees as well as other scientists from around the region to build an author team that was representative of the Northeast’s geography, institutional affiliation (federal agencies and academic and research institutions), depth of subject matter expertise, and knowledge of selected regional topics. Eleven authors were thus identified by December 2016, and the twelfth author was invited in April 2017 to better represent tribal knowledge in the chapter.
Lastly, the authors were contacted by the CL to determine their level of interest and willingness to serve as experts on the region's topics of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues.
The first two drafts of the Northeast chapter were structured around the themes of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues. During the USGCRP-sponsored Regional Engagement Workshop held in Boston on February 10, 2017, feedback was solicited from approximately 150 online participants (comprising transportation officials, coastal managers, urban planners, city managers, fisheries managers, forest managers, state officials, and others) around the Northeast and other parts of the United States, on both the content of these topical areas and important focal areas for the region. Additional inputs were solicited from other in-person meetings such as the ICNet workshop and American Association of Geographers meetings, both held in April 2017. All feedback was then compiled with the lessons learned from the USGCRP CLA-CL meeting in Washington, DC, also held in April 2017. On April 28, 2017, the author team met in Burlington, Vermont, and reworked the chapter’s structure around the risk-based framing of interest to 1) changing seasonality, 2) coastal/ocean resources, 3) rural communities and livelihoods, 4) urban interconnectedness, and 5) adaptation.
" report_identifier: nca4 statement: 'The Northeast’s urban centers and their interconnections are regional and national hubs for cultural and economic activity. Major negative impacts on critical infrastructure, urban economies, and nationally significant historic sites are already occurring and will become more common with a changing climate. (High Confidence)
' uncertainties: "Projecting changes in urban pollution and air quality under a changing climate is challenging given the associated complex chemistry and underlying factors that influence it. For example, fine particulates (PM2.5; that is, particles with a diameter of or less than 2.5 micrometers) are affected by cloud processes and precipitation, amongst other meteorological processes, leading to considerable uncertainty in the geographic distribution and overall trend in both modeling analysis and the literature.{{< tbib '29' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} Land use can also play an unexpected role, such as planting trees as a mitigation option that may lead to increases in volatile organic compounds (VOCs), which, in a VOC-limited environment that can exist in some urban areas such as New York City, may increase ozone concentrations (however, it is noted that most of the Northeast region is limited by the availability of nitrogen oxides).{{< tbib '327' '5b52af56-61c6-4663-9d7d-302e8570800f' >}}
Interdependencies among infrastructure sectors can lead to unexpected and amplified consequences in response to extreme weather events. However, it is unclear how society may choose to invest in the built environment, possibly strengthening urban infrastructure to plausible future conditions.
" uri: /report/nca4/chapter/northeast/finding/key-message-18-3 url: ~ - chapter_identifier: northeast confidence: 'There is very high confidence that extreme weather, warmer temperatures, degradation of air and water quality, and sea level rise threaten the health and well-being of people in the Northeast. There is very high confidence that these climate-related environmental changes will lead to additional adverse health-related impacts and costs, including premature deaths, more emergency department visits and hospitalizations, and lower quality of life. There is very high confidence that climate-related health impacts will vary by location, age, current health, and other characteristics of individuals and communities.
' evidence: "Extreme storms and temperatures, overall warmer temperatures, degradation of air and water quality, and sea level rise are all associated with adverse health outcomes from heat,{{< tbib '20' '6b3cd0ec-1e3e-42e8-ad82-5c12ed7ab0e8' >}},{{
It is understood that authors for a regional assessment must have scientific and regional credibility in the topical areas. Each author must also be willing and interested in serving in this capacity. Author selection for the Northeast chapter proceeded as follows:
First, the U.S. Global Change Research Program (USGCRP) released a Call for Public Nominations. Interested scientists were either nominated or self-nominated and their names placed into a database. The concurrent USGCRP Call for Public Nominations also solicited scientists to serve as chapter leads. Both lists were reviewed by the USGCRP with input from the coordinating lead author (CLA) and from the National Climate Assessment (NCA) Steering Committee. All regional chapter lead (CL) authors were selected by the USGCRP at the same time. The CLA and CL then convened to review the author nominations list as a “first cut” in identifying potential chapter authors for this chapter. Using their knowledge of the Northeast’s landscape and challenges, the CLA and CL used the list of national chapter topics that would be most relevant for the region. That topical list was associated with scientific expertise and a subset of the author list.
In the second phase, the CLA and CL used both the list of nominees as well as other scientists from around the region to build an author team that was representative of the Northeast’s geography, institutional affiliation (federal agencies and academic and research institutions), depth of subject matter expertise, and knowledge of selected regional topics. Eleven authors were thus identified by December 2016, and the twelfth author was invited in April 2017 to better represent tribal knowledge in the chapter.
Lastly, the authors were contacted by the CL to determine their level of interest and willingness to serve as experts on the region's topics of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues.
The first two drafts of the Northeast chapter were structured around the themes of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues. During the USGCRP-sponsored Regional Engagement Workshop held in Boston on February 10, 2017, feedback was solicited from approximately 150 online participants (comprising transportation officials, coastal managers, urban planners, city managers, fisheries managers, forest managers, state officials, and others) around the Northeast and other parts of the United States, on both the content of these topical areas and important focal areas for the region. Additional inputs were solicited from other in-person meetings such as the ICNet workshop and American Association of Geographers meetings, both held in April 2017. All feedback was then compiled with the lessons learned from the USGCRP CLA-CL meeting in Washington, DC, also held in April 2017. On April 28, 2017, the author team met in Burlington, Vermont, and reworked the chapter’s structure around the risk-based framing of interest to 1) changing seasonality, 2) coastal/ocean resources, 3) rural communities and livelihoods, 4) urban interconnectedness, and 5) adaptation.
" report_identifier: nca4 statement: 'Changing climate threatens the health and well-being of people in the Northeast through more extreme weather, warmer temperatures, degradation of air and water quality, and sea level rise (very high confidence). These environmental changes are expected to lead to health-related impacts and costs, including additional deaths, emergency room visits and hospitalizations, and a lower quality of life (very high confidence). Health impacts are expected to vary by location, age, current health, and other characteristics of individuals and communities (very high confidence).
' uncertainties: "Uncertainty remains in projections of the magnitude of future changes in particulate matter, humidity, and wildfires and how these changes may influence health risks. For example, health effects of future extreme heat may be exacerbated by future changes in absolute or relative humidity.
Health impacts are ultimately determined by not just the environmental hazard but also the amount of exposure, size and underlying susceptibility of the exposed population, and other factors such as health insurance coverage and access to timely healthcare services. In projecting future health risks, researchers acknowledge these challenges and use different analytic approaches to address this uncertainty or note it as a limitation.{{< tbib '23' '028a4c4b-3a7f-47b3-8a78-432fd7840f21' >}},{{
In addition, there is a paucity of literature that considers the joint or cumulative impacts on health of multiple climatic hazards. Additional areas where the literature base is limited include specific health impacts related to different types of climate-related migration, the impact of climatic factors on mental health, and the specific timing and geographic range of shifting disease-carrying vectors.
" uri: /report/nca4/chapter/northeast/finding/key-message-18-4 url: ~ - chapter_identifier: northeast confidence: 'There is high confidence that there are communities in the Northeast undertaking planning efforts to reduce risks posed from climate change and medium confidence that they are implementing climate adaptation. There is high confidence that decision support tools are informative and medium confidence that these communities are using decision support tools to find solutions for adaptation that are workable. There is high confidence that early adoption is occurring in some communities and that this provides a foundation for future efforts. This Key Message does not address trends into the future, and therefore likelihood is not applicable.
' evidence: "Reports on climate adaptation and resilience planning have been published by city, state, and tribal governments and by regional and federal agencies in the Northeast. Examples include the Interstate Commission on the Potomac River Basin (for the Washington, DC, metropolitan area),{{< tbib '304' '3258fcdc-5c7f-46a1-be18-29e440a0489a' >}} Boston,{{< tbib '295' '4d61fbc8-2282-49e8-bb8c-e7d87075f424' >}} the Port Authority of New York and New Jersey,{{< tbib '357' '62f465d8-b42c-42f7-81ec-0f5378ba9f19' >}} the St. Regis Mohawk Tribe,{{< tbib '360' '479edcdc-3e35-4859-86aa-5733316e0aa1' >}} the U.S. Army Corps of Engineers,{{< tbib '368' '641ac0a3-aad2-4422-a632-f07117fe694a' >}} the State of Maine,{{< tbib '381' 'a3a5fe5c-f49b-4c6b-a008-5647194a88a7' >}} and southeastern Connecticut.{{< tbib '417' '4afcd82e-a3d5-4d98-80e9-33ce546fabd9' >}} Structured decision-making is being applied to design management plans, determine research needs, and allocate resources{{< tbib '365' 'eddcff40-a0a0-426d-880b-a73730e9497f' >}} to preserve habitat and resources throughout the region.{{< tbib '151' '68fcc8c6-b20a-4739-aae6-e98b893d5163' >}},{{
It is understood that authors for a regional assessment must have scientific and regional credibility in the topical areas. Each author must also be willing and interested in serving in this capacity. Author selection for the Northeast chapter proceeded as follows:
First, the U.S. Global Change Research Program (USGCRP) released a Call for Public Nominations. Interested scientists were either nominated or self-nominated and their names placed into a database. The concurrent USGCRP Call for Public Nominations also solicited scientists to serve as chapter leads. Both lists were reviewed by the USGCRP with input from the coordinating lead author (CLA) and from the National Climate Assessment (NCA) Steering Committee. All regional chapter lead (CL) authors were selected by the USGCRP at the same time. The CLA and CL then convened to review the author nominations list as a “first cut” in identifying potential chapter authors for this chapter. Using their knowledge of the Northeast’s landscape and challenges, the CLA and CL used the list of national chapter topics that would be most relevant for the region. That topical list was associated with scientific expertise and a subset of the author list.
In the second phase, the CLA and CL used both the list of nominees as well as other scientists from around the region to build an author team that was representative of the Northeast’s geography, institutional affiliation (federal agencies and academic and research institutions), depth of subject matter expertise, and knowledge of selected regional topics. Eleven authors were thus identified by December 2016, and the twelfth author was invited in April 2017 to better represent tribal knowledge in the chapter.
Lastly, the authors were contacted by the CL to determine their level of interest and willingness to serve as experts on the region's topics of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues.
The first two drafts of the Northeast chapter were structured around the themes of water resources, agriculture and natural resources, oceans and marine ecosystems, coastal issues, health, and the built environment and urban issues. During the USGCRP-sponsored Regional Engagement Workshop held in Boston on February 10, 2017, feedback was solicited from approximately 150 online participants (comprising transportation officials, coastal managers, urban planners, city managers, fisheries managers, forest managers, state officials, and others) around the Northeast and other parts of the United States, on both the content of these topical areas and important focal areas for the region. Additional inputs were solicited from other in-person meetings such as the ICNet workshop and American Association of Geographers meetings, both held in April 2017. All feedback was then compiled with the lessons learned from the USGCRP CLA-CL meeting in Washington, DC, also held in April 2017. On April 28, 2017, the author team met in Burlington, Vermont, and reworked the chapter’s structure around the risk-based framing of interest to 1) changing seasonality, 2) coastal/ocean resources, 3) rural communities and livelihoods, 4) urban interconnectedness, and 5) adaptation.
" report_identifier: nca4 statement: 'Communities in the Northeast are proactively planning (high confidence) and implementing (medium confidence) actions to reduce risks posed by climate change. Using decision support tools to develop and apply adaptation strategies informs both the value of adopting solutions and the remaining challenges (high confidence). Experience since the last assessment provides a foundation to advance future adaptation efforts (high confidence).
' uncertainties: 'The percentage of communities in the Northeast that are planning for climate adaptation and resilience and the percentage of those using decision support tools are not known. More case studies would be needed to evaluate the effectiveness of adaptation actions.
' uri: /report/nca4/chapter/northeast/finding/key-message-18-5 url: ~ - chapter_identifier: southeast confidence: 'There is very high confidence that southeastern cities will likely be impacted by climate change, especially in the areas of infrastructure and human health.
' evidence: "Multiple studies have projected that urban areas, including those in the Southeast, will be adversely affected by climate change in a variety of ways. This includes impacts on infrastructure{{< tbib '41' '00e98394-26f1-45da-a5a3-e79b2b1a356f' >}},{{
Southeastern cities may be more vulnerable than cities in other regions of the United States due to the climate being more conducive to some vector-borne diseases, the presence of multiple large coastal cities at low elevation that are vulnerable to flooding and storms, and a rapidly growing urban and coastal population.{{< tbib '22' '446a98e1-77e4-4654-9125-277eab402a9f' >}},{{
Many city and county governments, utilities, and other government and service organizations have already begun to plan and prepare for the impacts of climate change (e.g., Gregg et al. 2017.; FTA 2013; City of Fayetteville 2017; City of Charleston 2015; City of New Orleans 2015; Tampa Bay Water 2014; EPA 2015; City of Atlanta 2015, 2017; Southeast Florida Regional Climate Change Compact 2017{{< tbib '44' '29100037-c24e-4309-b6a2-e4397db7ed01' >}},{{
Prior to identifying critical issues for the Southeast assessment focuses for the Fourth National Climate Assessment (NCA4), the Chapter Lead (CL) contacted numerous professional colleagues representing various geographic areas (e.g., Florida, Louisiana, and South Carolina) for expert opinions on critical climate change related issues impacting the region, with a particular emphasis on emerging issues since the Third National Climate Assessment (NCA3) effort.{{< tbib '77' '7bdd9d20-6e83-40ab-8d50-68272c2b3dc9' >}} Following those interviews, the CL concluded that the most pressing climate change issues to focus on for the NCA4 effort were extreme events, flooding (both from rainfall and sea level rise), wildfire, health issues, ecosystems, and adaptation actions. Authors with specific expertise in each of these areas were sought, and a draft outline built around these issues was developed. Further refinement of these focal areas occurred in conjunction with the public Regional Engagement Workshop, held on the campus of North Carolina State University in March 2017 and in six satellite locations across the Southeast region. The participants agreed that the identified issues were important and suggested the inclusion of several other topics, including impacts on coastal and rural areas and people, forests, and agriculture. Based on the subsequent authors’ meeting and input from NCA staff, the chapter outline and Key Messages were updated to reflect a risk-based framing in the context of a new set of Key Messages. The depth of discussion for any particular topic and Key Message is dependent on the availability of supporting literature and chapter length limitations.
" report_identifier: nca4 statement: 'Many southeastern cities are particularly vulnerable to climate change compared to cities in other regions, with expected impacts to infrastructure and human health (very likely, very high confidence). The vibrancy and viability of these metropolitan areas, including the people and critical regional resources located in them, are increasingly at risk due to heat, flooding, and vector-borne disease brought about by a changing climate (likely, high confidence). Many of these urban areas are rapidly growing and offer opportunities to adopt effective adaptation efforts to prevent future negative impacts of climate change (very likely, high confidence).
' uncertainties: 'Population projections are inherently uncertain over long time periods, and shifts in immigration or migration rates and shifting demographics will influence urban vulnerabilities to climate change. The precise impacts on cities are difficult to project. The scope and scale of adaptation efforts, which are already underway, will affect future vulnerability and risk. Technological developments (such as a potential shift in transportation modes) will also affect the scope and location of risk within cities. Newly emerging pathogens could increase risk of disease in the future, while successful adaptations could reduce public health risk.
' uri: /report/nca4/chapter/southeast/finding/key-message-19-1 url: ~ - chapter_identifier: southeast confidence: 'There is high confidence that flood risks will very likely increase in coastal and low-lying regions of the Southeast due to rising sea level and an increase in extreme rainfall events. There is high confidence that Southeast coastal cities are already experiencing record numbers of high tide flooding events, and without significant adaptation measures, it is likely they will be impacted by daily high tide flooding.
' evidence: "Multiple lines of research have shown that global sea levels have increased in the past and are projected to continue to accelerate in the future due to increased global temperature and that higher local sea level rise rates in the Mid-Atlantic and Gulf Coasts have occurred.{{< tbib '51' '3bae2310-7572-47e2-99a4-9e4276764934' >}},{{
Annual occurrences of high tide flooding have increased, causing several Southeast coastal cities to experience all-time records of occurrences that are posing daily risks.{{< tbib '1' 'df029572-7e7a-4f65-91c2-da86756620c4' >}},{{
There is scientific consensus that sea level rise will continue to cause increases in high tide flooding in the Southeast as well as impact the frequency and duration of extreme water level events, causing an increase in the vulnerability of coastal populations and property.{{< tbib '1' 'df029572-7e7a-4f65-91c2-da86756620c4' >}},{{
In the future, coastal flooding is projected to become more serious, disruptive, and costly as the frequency, depth, and inland extent grow with time.{{< tbib '1' 'df029572-7e7a-4f65-91c2-da86756620c4' >}},{{
Many analyses have determined that extreme rainfall events have increased in the Southeast, and under higher scenarios, the frequency and intensity of these events are projected to increase.{{< tbib '19' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}},{{
Rainfall records have shown that since NCA3, many intense rainfall events (approaching 500-year events) have occurred in the Southeast, with some causing billions of dollars in damage and many deaths.{{< tbib '68' '03e51664-273d-40e5-8af0-ab885436ac8e' >}},{{
The flood events in Baton Rouge, Louisiana, in 2016 and in South Carolina in 2015 provide real examples of how vulnerable inland and coastal communities are to extreme rainfall events.{{< tbib '81' '6acb342f-f144-4fad-ae46-a6ff80f812cf' >}},{{
The socioeconomic impacts of climate change on the Southeast is a developing research field.{{< tbib '65' 'e1f4f1b2-6b77-465a-bddb-ed992079deea' >}},{{
Prior to identifying critical issues for the Southeast assessment focuses for the Fourth National Climate Assessment (NCA4), the Chapter Lead (CL) contacted numerous professional colleagues representing various geographic areas (e.g., Florida, Louisiana, and South Carolina) for expert opinions on critical climate change related issues impacting the region, with a particular emphasis on emerging issues since the Third National Climate Assessment (NCA3) effort.{{< tbib '77' '7bdd9d20-6e83-40ab-8d50-68272c2b3dc9' >}} Following those interviews, the CL concluded that the most pressing climate change issues to focus on for the NCA4 effort were extreme events, flooding (both from rainfall and sea level rise), wildfire, health issues, ecosystems, and adaptation actions. Authors with specific expertise in each of these areas were sought, and a draft outline built around these issues was developed. Further refinement of these focal areas occurred in conjunction with the public Regional Engagement Workshop, held on the campus of North Carolina State University in March 2017 and in six satellite locations across the Southeast region. The participants agreed that the identified issues were important and suggested the inclusion of several other topics, including impacts on coastal and rural areas and people, forests, and agriculture. Based on the subsequent authors’ meeting and input from NCA staff, the chapter outline and Key Messages were updated to reflect a risk-based framing in the context of a new set of Key Messages. The depth of discussion for any particular topic and Key Message is dependent on the availability of supporting literature and chapter length limitations.
" report_identifier: nca4 statement: 'The Southeast’s coastal plain and inland low-lying regions support a rapidly growing population, a tourism economy, critical industries, and important cultural resources that are highly vulnerable to climate change impacts (very likely, very high confidence). The combined effects of changing extreme rainfall events and sea level rise are already increasing flood frequencies, which impacts property values and infrastructure viability, particularly in coastal cities. Without significant adaptation measures, these regions are projected to experience daily high tide flooding by the end of the century (likely, high confidence).
' uncertainties: 'The amount of confidence associated with the historical rate of global sea level rise is impacted by the sparsity of tide gauge records and historical proxies as well as different statistical approaches for estimating sea level change. The amount of unpredictability in future projected rates of sea level rise is likely caused by a range of future climate scenarios projections and rate of ice sheet mass changes. Flooding events are highly variable in both space and time. Detection and attribution of flood events are difficult due to multiple variables that cause flooding.
' uri: /report/nca4/chapter/southeast/finding/key-message-19-2 url: ~ - chapter_identifier: southeast confidence: 'There is high confidence that climate change (e.g., changing winter temperatures extremes, changing fire regimes, rising sea levels and hurricanes, warming ocean temperatures, and more extreme rainfall and drought) will very likely affect natural systems in the Southeast region. These climatic drivers play critical roles and greatly influence the distribution, structure, and functioning of ecosystems; hence, changes in these climatic drivers will transform ecosystems in the region and greatly alter the distribution and abundance of species.
' evidence: "Winter temperature extremes, fire regimes, sea levels, hurricanes, rainfall extremes, drought extremes, and warming ocean temperatures greatly influence the distribution, abundance, and performance of species and ecosystems.
Winter air temperature extremes (for example, freezing and chilling events) constrain the northern limit of many tropical and subtropical species.{{< tbib '30' '9cef8d69-7596-480a-81b6-abd09ff1c1e3' >}},{{
Changing fire regimes are expected to have a large impact on natural systems. Fire has historically played an important role in the region, and ecological diversity in many southeastern natural systems is dependent upon fire.{{< tbib '115' '56b229a1-fc34-4010-9b6e-3ab94c77b49c' >}},{{
Hurricanes and rising sea levels are aspects of climate change that will have a tremendous effect on coastal ecosystems in the Southeast. Historically, coastal ecosystems in the region have adjusted to sea level rise via vertical and/or horizontal movement across the landscape.{{< tbib '125' '6c5f197a-cfe5-4433-9bce-2c53a1939f2d' >}},{{
Climate change is expected to intensify the hydrologic cycle and increase the frequency and severity of extreme events. Extreme drought events are expected to become more frequent and severe. Drought and extreme heat can result in tree mortality and transform southeastern forested ecosystems.{{< tbib '217' 'a073cf8e-8d74-4f11-bfe2-d3494b9bcc7a' >}},{{
Warming ocean temperatures due to climate change are expected to have a large effect on marine and coastal ecosystems.{{< tbib '234' 'cfdaea11-95e2-4789-914b-74901b2f26b0' >}},{{
Prior to identifying critical issues for the Southeast assessment focuses for the Fourth National Climate Assessment (NCA4), the Chapter Lead (CL) contacted numerous professional colleagues representing various geographic areas (e.g., Florida, Louisiana, and South Carolina) for expert opinions on critical climate change related issues impacting the region, with a particular emphasis on emerging issues since the Third National Climate Assessment (NCA3) effort.{{< tbib '77' '7bdd9d20-6e83-40ab-8d50-68272c2b3dc9' >}} Following those interviews, the CL concluded that the most pressing climate change issues to focus on for the NCA4 effort were extreme events, flooding (both from rainfall and sea level rise), wildfire, health issues, ecosystems, and adaptation actions. Authors with specific expertise in each of these areas were sought, and a draft outline built around these issues was developed. Further refinement of these focal areas occurred in conjunction with the public Regional Engagement Workshop, held on the campus of North Carolina State University in March 2017 and in six satellite locations across the Southeast region. The participants agreed that the identified issues were important and suggested the inclusion of several other topics, including impacts on coastal and rural areas and people, forests, and agriculture. Based on the subsequent authors’ meeting and input from NCA staff, the chapter outline and Key Messages were updated to reflect a risk-based framing in the context of a new set of Key Messages. The depth of discussion for any particular topic and Key Message is dependent on the availability of supporting literature and chapter length limitations.
" report_identifier: nca4 statement: 'The Southeast’s diverse natural systems, which provide many benefits to society, will be transformed by climate change (very likely, high confidence). Changing winter temperature extremes, wildfire patterns, sea levels, hurricanes, floods, droughts, and warming ocean temperatures are expected to redistribute species and greatly modify ecosystems (very likely, high confidence). As a result, the ecological resources that people depend on for livelihood, protection, and well-being are increasingly at risk, and future generations can expect to experience and interact with natural systems that are much different than those that we see today (very likely, high confidence).
' uncertainties: 'In the Southeast, winter temperature extremes, fire regimes, sea level fluctuations, hurricanes, extreme rainfall, and extreme drought all play critical roles and greatly influence the distribution, structure, and function of species and ecosystems. Changing climatic conditions (particularly, changes in the frequency and severity of climate extremes) are, however, difficult to replicate via experimental manipulations; hence, ecological responses to future climate regimes have not been fully quantified for all species and ecosystems. Natural ecosystems are complex and governed by many interacting biotic and abiotic processes. Although it is possible to make general predictions of climate change effects, specific future ecological transformations can be difficult to predict, especially given the number of interacting and changing biotic and abiotic factors in any specific location. Uncertainties in the range of potential future changes in multiple and concurrent facets of climate and land-use change also affect our ability to predict changes to natural systems.
' uri: /report/nca4/chapter/southeast/finding/key-message-19-3 url: ~ - chapter_identifier: southeast confidence: 'There is high confidence that climate change (e.g., rising temperatures, changing fire regimes, rising sea levels, and more extreme rainfall and drought) will very likely affect agricultural and forest products industries, potentially resulting in economic impacts. There is high confidence that increases in temperature are very likely to increase heat-related illness, deaths, and loss of labor productivity without greater adaptation efforts.
' evidence: "Analysis of the sensitivity of some manufacturing sectors to climate changes anticipates secondary risks associated with crop and livestock productivity.{{< tbib '64' '9f559c9b-c78e-4593-bcbe-f07661d29e16' >}},{{
Multiple analyses anticipate that energy- or water-intensive industries could face water stress and increased energy costs.{{< tbib '8' '75a38932-a8a4-4eeb-b94c-bbb65b580efe' >}},{{
A large body of evidence addresses the sensitivity of many crops grown in the Southeast to changing climate conditions including increased temperatures, decreased summer rainfall, drought, and change in the timing and duration of chill periods.{{< tbib '7' 'cc31a438-8e10-4957-88f9-cb6e763e2b5e' >}},{{
Multiple lines of evidence indicate that forests are likely to be impacted by changing climate, particularly moisture regimes and potential changes in wildfire activity.{{< tbib '191' 'a182cf3b-2113-4680-99e8-4e17abed758a' >}},{{
Rural communities tend to be vulnerable due to factors such as demography, occupations, earnings, literacy, and poverty incidence.{{< tbib '8' '75a38932-a8a4-4eeb-b94c-bbb65b580efe' >}},{{
Prior to identifying critical issues for the Southeast assessment focuses for the Fourth National Climate Assessment (NCA4), the Chapter Lead (CL) contacted numerous professional colleagues representing various geographic areas (e.g., Florida, Louisiana, and South Carolina) for expert opinions on critical climate change related issues impacting the region, with a particular emphasis on emerging issues since the Third National Climate Assessment (NCA3) effort.{{< tbib '77' '7bdd9d20-6e83-40ab-8d50-68272c2b3dc9' >}} Following those interviews, the CL concluded that the most pressing climate change issues to focus on for the NCA4 effort were extreme events, flooding (both from rainfall and sea level rise), wildfire, health issues, ecosystems, and adaptation actions. Authors with specific expertise in each of these areas were sought, and a draft outline built around these issues was developed. Further refinement of these focal areas occurred in conjunction with the public Regional Engagement Workshop, held on the campus of North Carolina State University in March 2017 and in six satellite locations across the Southeast region. The participants agreed that the identified issues were important and suggested the inclusion of several other topics, including impacts on coastal and rural areas and people, forests, and agriculture. Based on the subsequent authors’ meeting and input from NCA staff, the chapter outline and Key Messages were updated to reflect a risk-based framing in the context of a new set of Key Messages. The depth of discussion for any particular topic and Key Message is dependent on the availability of supporting literature and chapter length limitations.
" report_identifier: nca4 statement: 'Rural communities are integral to the Southeast’s cultural heritage and to the strong agricultural and forest products industries across the region. More frequent extreme heat episodes and changing seasonal climates are projected to increase exposure-linked health impacts and economic vulnerabilities in the agricultural, timber, and manufacturing sectors (very likely, high confidence). By the end of the century, over one-half billion labor hours could be lost from extreme heat-related impacts (likely, medium confidence). Such changes would negatively impact the region’s labor-intensive agricultural industry and compound existing social stresses in rural areas related to limited local community capabilities and associated with rural demography, occupations, earnings, literacy, and poverty incidence (very likely, high confidence). Reduction of existing stresses can increase resilience (very likely, high confidence).
' uncertainties: "There are limited studies documenting direct connections between climate changes and economic impacts. Models are limited in their ability to incorporate adaptation that may reduce losses. These factors restrict the potential to strongly associate declines in agricultural and forest productivity with the level of potential economic impact.
Projections of potential change in the frequency and extent of wildfires depend in part on models of future population growth and human behavior, which are limited, adding to the uncertainty associated with climate and forest modeling.
Many indicators of vulnerability are dynamic, so that adaptation and other changes can affect the patterns of vulnerability to heat and other climate stressors over time. Limited studies indicate concerns over the planning and preparedness of capacity at local levels; however, information is limited.
Projected labor hours lost vary by global climate model, time frame, and scenario, with a mean of 0.57 and a model range of 0.34–0.82 billion labor hours lost each year for RCP8.5 by 2090. The annual mean projected losses are roughly halved (0.28 billion labor hours) and with a model range from 0.19 to 0.43 billion labor hours lost under RCP4.5 by 2090.{{< tbib '35' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}}
" uri: /report/nca4/chapter/southeast/finding/key-message-19-4 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is very high confidence for a major human influence on climate.
Assessments of the natural forcings of solar irradiance changes and volcanic activity show with very high confidence that both forcings are small over the industrial era relative to total anthropogenic forcing. Total anthropogenic forcing is assessed to have become larger and more positive during the industrial era, while natural forcings show no similar trend.
' evidence: "The Key Message and supporting text summarize extensive evidence documented in the climate science literature and are similar to statements made in previous national (NCA3){{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} and international{{< tbib '249' 'f03117be-ccfe-4f88-b70a-ffd4351b8190' >}} assessments. The human effects on climate have been well documented through many papers in the peer-reviewed scientific literature (e.g., see Fahey et al. 2017{{< tbib '18' '0615b4ff-d185-4e14-9d4d-5bea1ce6ca51' >}} and Knutson et al. 2017{{< tbib '16' '0725eae6-7458-4ec2-8f66-880d88118148' >}} for more discussion of supporting evidence).
The finding of an increasingly strong positive forcing over the industrial era is supported by observed increases in atmospheric temperatures (see Wuebbles et al. 2017{{< tbib '10' '666daffe-2c3b-4e2d-9157-16b989860618' >}}) and by observed increases in ocean temperatures.{{< tbib '10' '666daffe-2c3b-4e2d-9157-16b989860618' >}},{{
This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Global climate is changing rapidly compared to the pace of natural variations in climate that have occurred throughout Earth’s history. Global average temperature has increased by about 1.8°F from 1901 to 2016, and observational evidence does not support any credible natural explanations for this amount of warming; instead, the evidence consistently points to human activities, especially emissions of greenhouse or heat-trapping gases, as the dominant cause. (Very High Confidence)
' uncertainties: "Key remaining uncertainties relate to the precise magnitude and nature of changes at global, and particularly regional, scales and especially for extreme events and our ability to simulate and attribute such changes using climate models. The exact effects from land-use changes relative to the effects from greenhouse gas emissions need to be better understood.
The largest source of uncertainty in radiative forcing (both natural and anthropogenic) over the industrial era is quantifying forcing by aerosols. This finding is consistent across previous assessments (e.g., IPCC 2007, IPCC 2013{{< tbib '249' 'f03117be-ccfe-4f88-b70a-ffd4351b8190' >}},{{
Recent work has highlighted the potentially larger role of variations in ultraviolet solar irradiance, versus total solar irradiance, in solar forcing. However, this increase in solar forcing uncertainty is not sufficiently large to reduce confidence that anthropogenic activities dominate industrial-era forcing.
" uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-1 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is very high confidence in the likelihood of the existence of positive feedbacks and tipping elements based on a large body of literature published over the last 25 years that draws from basic physics, observations, paleoclimate data, and modeling.
There is very high confidence that some feedbacks can be quantified, others are known but cannot be quantified, and others may yet exist that are currently unknown.
There is very high confidence that the models are incomplete representations of the real world; and there is medium confidence that their tendency is to under- rather than overestimate the amount of long-term future change.
' evidence: "This Key Message is based on a large body of scientific literature recently summarized by Lenton et al. (2008),{{< tbib '197' 'd64a3dbf-d45e-49de-98b9-b4ea32da888f' >}} NRC (2013),{{< tbib '339' '3dcd5a73-de83-4b37-884a-5236407c170e' >}} and Kopp et al. (2016).{{< tbib '198' '08bc6610-586b-421c-a788-f5e18781ac52' >}} As NRC (2013){{< tbib '339' '3dcd5a73-de83-4b37-884a-5236407c170e' >}} states, “A study of Earth’s climate history suggests the inevitability of ‘tipping points’—thresholds beyond which major and rapid changes occur when crossed—that lead to abrupt changes in the climate system” and “Can all tipping points be foreseen? Probably not. Some will have no precursors, or may be triggered by naturally occurring variability in the climate system. Some will be difficult to detect, clearly visible only after they have been crossed and an abrupt change becomes inevitable.” As IPCC AR5 WG1 Chapter 12, Section 12.5.5{{< tbib '26' 'b3bbc7b5-067e-4c23-8d9b-59faee21e58e' >}} further states, “A number of components or phenomena within the Earth system have been proposed as potentially possessing critical thresholds (sometimes referred to as tipping points) beyond which abrupt or nonlinear transitions to a different state ensues.” Collins et al. (2013){{< tbib '26' 'b3bbc7b5-067e-4c23-8d9b-59faee21e58e' >}} further summarize critical thresholds that can be modeled and others that can only be identified.
This Key Message is also based on the conclusions of IPCC AR5 WG1,{{< tbib '249' 'f03117be-ccfe-4f88-b70a-ffd4351b8190' >}} specifically Chapter 7;{{< tbib '196' 'a46eaad1-5c17-46f7-bba6-d3fee718a092' >}} the state of the art of global models is briefly summarized in Hayhoe et al. (2017).{{< tbib '24' '9c909a77-a1d9-477d-82fc-468a6b1af771' >}} This Key Message is also based upon the tendency of global climate models to underestimate, relative to geological reconstructions, the magnitude of both long-term global mean warming and the amplification of warming at high latitudes in past warm climates (e.g., Salzmann et al. 2013, Goldner et al. 2014, Caballeo and Huber 2013, Lunt et al. 2012{{< tbib '199' '9f061a0a-e32d-417f-8404-c5ad0d4b01f4' >}},{{
This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'The climate change resulting from human-caused emissions of carbon dioxide will persist for decades to millennia. Self-reinforcing cycles within the climate system have the potential to accelerate human-induced change and even shift Earth’s climate system into new states that are very different from those experienced in the recent past. Future changes outside the range projected by climate models cannot be ruled out (very high confidence), and due to their systematic tendency to underestimate temperature change during past warm periods, models may be more likely to underestimate than to overestimate long-term future change (medium confidence).
' uncertainties: 'The largest uncertainties are 1) whether proposed tipping elements actually undergo critical transitions, 2) the magnitude and timing of forcing that will be required to initiate critical transitions in tipping elements, 3) the speed of the transition once it has been triggered, 4) the characteristics of the new state that results from such transition, and 5) the potential for new positive feedbacks and tipping elements to exist that are yet unknown.
The largest uncertainties in models are structural: are the models including all the important components and relationships necessary to model the feedbacks and, if so, are these correctly represented in the models?
' uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-10 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is very high confidence for continued changes in climate and high confidence for the levels shown in the Key Message.
' evidence: "The Key Message and supporting text summarize extensive evidence documented in the climate science literature and are similar to statements made in previous national (NCA3){{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} and international{{< tbib '249' 'f03117be-ccfe-4f88-b70a-ffd4351b8190' >}} assessments. The projections for future climate have been well documented through many papers in the peer reviewed scientific literature (e.g., see Hayhoe et al. 2017{{< tbib '24' '9c909a77-a1d9-477d-82fc-468a6b1af771' >}} for descriptions of the scenarios and the models used).
" href: https://data.globalchange.gov/report/nca4/chapter/our-changing-climate/finding/key-message-2-2.yaml identifier: key-message-2-2 ordinal: 2 process: "This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Earth’s climate will continue to change over this century and beyond (very high confidence). Past mid-century, how much the climate changes will depend primarily on global emissions of greenhouse gases and on the response of Earth’s climate system to human-induced warming (very high confidence). With significant reductions in emissions, global temperature increase could be limited to 3.6°F (2°C) or less compared to preindustrial temperatures (high confidence). Without significant reductions, annual average global temperatures could increase by 9°F (5°C) or more by the end of this century compared to preindustrial temperatures (high confidence).
' uncertainties: 'Key remaining uncertainties relate to the precise magnitude and nature of changes at global, and particularly regional scales, and especially for extreme events and our ability to simulate and attribute such changes using climate models. Of particular importance are remaining uncertainties in the understanding of feedbacks in the climate system, especially in ice–albedo and cloud cover feedbacks. Continued improvements in climate modeling to represent the physical processes affecting the Earth’s climate system are aimed at reducing uncertainties. Enhanced monitoring and observation programs also can help improve the understanding needed to reduce uncertainties.
' uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-2 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is very high confidence in measurements that show increases in the ocean heat content and warming of the ocean, based on the agreement of different methods. However, long-term data in total ocean heat uptake in the deep ocean are sparse, leading to limited knowledge of the transport of heat between and within ocean basins.
Major ocean deoxygenation is taking place in bodies of water inland, at estuaries, and in the coastal and the open ocean (high confidence). Regionally, the phenomenon is exacerbated by local changes in weather, ocean circulation, and continental inputs to the oceans.
' evidence: "The Key Message and supporting text summarize the evidence documented in climate science literature as summarized in Rhein et al. (2013).{{< tbib '31' 'bc140b4c-c2d9-4d99-a684-5c054dc5134f' >}} Oceanic warming has been documented in a variety of data sources, most notably by the World Ocean Circulation Experiment (WOCE),{{< tbib '251' '4ef3eb98-3ce7-4c94-8b1b-9a09ee951bfd' >}} Argo,{{< tbib '252' '295cc0c4-536f-49c5-abdc-3a3b4916fdba' >}} and the Extended Reconstructed Sea Surface Temperature v4 (ERSSTv4).{{< tbib '253' '865e132e-dd4a-4195-9ea0-c3c7d32d447e' >}} There is particular confidence in calculated warming for the time period since 1971 due to increased spatial and depth coverage and the level of agreement among independent sea surface temperature (SST) observations from satellites, surface drifters and ships, and independent studies using differing analyses, bias corrections, and data sources.{{< tbib '20' 'db777261-ee2e-4bf6-944e-a8831c595300' >}},{{
Evidence for oxygen trends arises from extensive global measurements of WOCE after 1989 and individual profiles before that.{{< tbib '43' '2dbd3f8b-a4f8-421f-b75f-8cb165b1a867' >}} The first basin-wide dissolved oxygen surveys were performed in the 1920s.{{< tbib '255' 'b2a0160d-032f-4a96-8cb1-321e09950172' >}} The confidence level is based on globally integrated O2 distributions in a variety of ocean models. Although the global mean exhibits low interannual variability, regional contrasts are large.
" href: https://data.globalchange.gov/report/nca4/chapter/our-changing-climate/finding/key-message-2-3.yaml identifier: key-message-2-3 ordinal: 3 process: "This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'The world’s oceans have absorbed 93% of the excess heat from human-induced warming since the mid-20th century and are currently absorbing more than a quarter of the carbon dioxide emitted to the atmosphere annually from human activities, making the oceans warmer and more acidic (very high confidence). Increasing sea surface temperatures, rising sea levels, and changing patterns of precipitation, winds, nutrients, and ocean circulation are contributing to overall declining oxygen concentrations in many locations (high confidence).
' uncertainties: 'Uncertainties in the magnitude of ocean warming stem from the disparate measurements of ocean temperature over the last century. There is high confidence in warming trends of the upper ocean temperature from 0–700 m depth, whereas there is more uncertainty for deeper ocean depths of 700–2,000 m due to the short record of measurements from those areas. Data on warming trends at depths greater than 2,000 m are even more sparse. There are also uncertainties in the timing and reasons for particular decadal and interannual variations in ocean heat content and the contributions that different ocean basins play in the overall ocean heat uptake.
Uncertainties in ocean oxygen content (as estimated from the intermodel spread) in the global mean are moderate mainly because ocean oxygen content exhibits low interannual variability when globally averaged. Uncertainties in long-term decreases of the global averaged oxygen concentration amount to 25% in the upper 1,000 m for the 1970–1992 period and 28% for the 1993–2003 period. Remaining uncertainties relate to regional variability driven by mesoscale eddies and intrinsic climate variability such as ENSO.
' uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-3 url: ~ - chapter_identifier: our-changing-climate confidence: 'This Key Message is based upon multiple analyses of tide gauge and satellite altimetry records, on a meta-analysis of multiple geological proxies for pre-instrumental sea level change, and on both statistical and physical analyses of the human contribution to GMSL rise since 1900.
It is also based upon multiple methods for estimating the probability of future sea level change and on new modeling results regarding the stability of marine-based ice in Antarctica.
Confidence is very high in the rate of GMSL rise since 1900, based on multiple different approaches to estimating GMSL rise from tide gauges and satellite altimetry. Confidence is high in the substantial human contribution to GMSL rise since 1900, based on both statistical and physical modeling evidence. There is medium confidence that the magnitude of the observed rise since 1900 is unprecedented in the context of the previous 2,700 years, based on meta-analysis of geological proxy records.
There is very high confidence that GMSL rise over the next several decades will be at least as fast as a continuation of the historical trend over the last quarter century would indicate. There is medium confidence in the upper end of very likely ranges for 2030 and 2050. Due to possibly large ice sheet contributions, there is low confidence in the upper end of very likely ranges for 2100. Based on multiple projection methods, there is high confidence that differences between scenarios are small before 2050 but significant beyond 2050.
' evidence: "Multiple researchers, using different statistical approaches, have integrated tide gauge records to estimate global mean sea level (GMSL) rise since the late 19th century (e.g., Church and White 2006, 2011; Hay et al. 2015; Jevrejeva et al. 2009{{< tbib '61' '1295b731-1d4c-44e2-b877-74df46d8e58d' >}},{{
The finding regarding the historical context of the 20th-century change is based upon Kopp et al. (2016),{{< tbib '58' 'a0130167-b319-493d-bedc-7cab8f8fe9d9' >}} who conducted a meta-analysis of geological regional sea level (RSL) reconstructions, spanning the last 3,000 years, from 24 locations around the world, as well as tide gauge data from 66 sites and the tide-gauge-based GMSL reconstruction of Hay et al. (2015).{{< tbib '73' '7c318710-b8fb-4e09-9982-546f2b60be67' >}} By constructing a spatiotemporal statistical model of these datasets, they identified the common global sea level signal over the last three millennia, and its uncertainties. They found a 95% probability that the average rate of GMSL change over 1900–2000 was greater than during any preceding century in at least 2,800 years.
The lower bound of the very likely range is based on a continuation of the observed, approximately 3 mm/year rate of GMSL rise. The upper end of the very likely range is based on estimates for a higher scenario (RCP8.5) from three studies producing fully probabilistic projections across multiple RCPs. Kopp et al.(2014){{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} fused multiple sources of information accounting for the different individual process contributing to GMSL rise. Kopp et al. (2016){{< tbib '58' 'a0130167-b319-493d-bedc-7cab8f8fe9d9' >}} constructed a semi-empirical sea level model calibrated to the Common Era sea level reconstruction. Mengel et al. (2016){{< tbib '257' '94117a50-acc5-4dbf-8029-368aa3fc9680' >}} constructed a set of semi-empirical models of the different contributing processes. All three studies show negligible scenario dependence in the first half of this century but increasing in prominence in the second half of the century. A sensitivity study by Kopp et al. (2014),{{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} as well as studies by Jevrejeva et al. (2014){{< tbib '78' 'be9f25a7-6fb1-4599-b971-47aeb2abf967' >}} and by Jackson and Jevrejeva (2016),{{< tbib '258' 'c748bd06-bc78-4b9c-b511-7dab1974211e' >}} used frameworks similar to Kopp et al. (2016){{< tbib '58' 'a0130167-b319-493d-bedc-7cab8f8fe9d9' >}} but incorporated an expert elicitation study on ice sheet stability.{{< tbib '259' '86851f34-1534-4feb-aa11-8e0d7eeb0b11' >}} (This study was incorporated in the main results of Kopp et al. 2014{{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} with adjustments for consistency with Church et al. 2013.{{< tbib '56' 'da0fddf2-c9c9-40d0-8e33-a86342d8b864' >}}) These studies extend the very likely range for RCP8.5 as high as 5–6 feet (160–180 cm; see Kopp et al. 2014, sensitivity study; Jevrejeva et al. 2014; Jackson and Jevrejeva 2016).{{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}},{{< tbib '78' 'be9f25a7-6fb1-4599-b971-47aeb2abf967' >}},{{
As described in Sweet et al. (2017),{{< tbib '57' '3bae2310-7572-47e2-99a4-9e4276764934' >}} Miller et al. (2013),{{< tbib '260' 'b58704d1-b4ec-46d0-9dd5-e7573523951e' >}} and Kopp et al. (2017),{{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} several lines of arguments exist that support a plausible worst-case GMSL rise scenario in the range of 2.0 m to 2.7 m by 2100. Pfeffer et al. (2008){{< tbib '261' 'bfa425f2-e044-44c2-8bdb-5f8491c577de' >}} constructed a “worst-case” 2.0 m scenario, based on acceleration of mass loss from Greenland, that assumed a 30 cm GMSL contribution from thermal expansion. However, Sriver et al. (2012){{< tbib '262' 'b15cbb81-a2ac-4201-a184-a361bbd238d6' >}} find a physically plausible upper bound from thermal expansion exceeding 50 cm (an additional ~20-cm increase). The ~60 cm maximum contribution by 2100 from Antarctica in Pfeffer et al. (2008){{< tbib '261' 'bfa425f2-e044-44c2-8bdb-5f8491c577de' >}} could be exceeded by ~30 cm, assuming the 95th percentile for Antarctic melt rate (~22 mm/year) of the Bamber and Aspinall (2013){{< tbib '259' '86851f34-1534-4feb-aa11-8e0d7eeb0b11' >}} expert elicitation study is achieved by 2100 through a linear growth in melt rate. The Pfeffer et al. (2008){{< tbib '261' 'bfa425f2-e044-44c2-8bdb-5f8491c577de' >}} study did not include the possibility of a net decrease in land-water storage due to groundwater withdrawal; Church et al. (2013){{< tbib '56' 'da0fddf2-c9c9-40d0-8e33-a86342d8b864' >}} find a likely land-water storage contribution to 21st century GMSL rise of −1 cm to +11 cm. These arguments all point to the physical plausibility of GMSL rise in excess of 8 feet (240 cm).
Additional arguments come from model results examining the effects of marine ice-cliff collapse and ice-shelf hydro-fracturing on Antarctic loss rates.{{< tbib '80' 'ae82c8a3-3033-4103-91e9-926a27d1fa18' >}} To estimate the effect of incorporating the DeConto and Pollard (2016){{< tbib '80' 'ae82c8a3-3033-4103-91e9-926a27d1fa18' >}} projections of Antarctic ice sheet melt, Kopp et al. (2017){{< tbib '81' '387b7906-07c3-431f-a441-5a103220a974' >}} substituted the bias-corrected ensemble of DeConto and Pollard{{< tbib '80' 'ae82c8a3-3033-4103-91e9-926a27d1fa18' >}} into the Kopp et al. (2014){{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} framework. This elevates the projections for 2100 to 3.1–8.9 feet (93–243 cm) for RCP8.5, 1.6–5.2 feet (50–158 cm) for RCP4.5, and 0.9–3.2 feet (26–98 cm) for RCP2.6. DeConto and Pollard{{< tbib '80' 'ae82c8a3-3033-4103-91e9-926a27d1fa18' >}} is just one study, not designed in a manner intended to produce probabilistic projections, and so these results cannot be used to ascribe probability; they do, however, support the physical plausibility of GMSL rise in excess of 8 feet.
Very likely ranges, 2030 relative to 2000 in cm (feet)| Kopp et al. (2014){{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} | Kopp et al. (2016){{< tbib '58' 'a0130167-b319-493d-bedc-7cab8f8fe9d9' >}} | Kopp et al. (2017){{< tbib '81' '387b7906-07c3-431f-a441-5a103220a974' >}} DP16 | Mengel et al. (2016){{< tbib '257' '94117a50-acc5-4dbf-8029-368aa3fc9680' >}} | |
| RCP8.5 (higher) | 11–18 (0.4–0.6) | 8–15 (0.3–0.5) | 6–22 (0.2–0.7) | 7–12 (0.2–0.4) |
| RCP4.5 (lower) | 10–18 (0.3–0.6) | 8–15 (0.3–0.5) | 6–23 (0.2–0.8) | 7–12 (0.2–0.4) |
| RCP2.6 (very low) | 10–18 (0.3–0.6) | 8–15 (0.3–0.5) | 6–23 (0.2–0.8) | 7–12 (0.2–0.4) |
| Kopp et al. (2014){{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} | Kopp et al. (2016){{< tbib '58' 'a0130167-b319-493d-bedc-7cab8f8fe9d9' >}} | Kopp et al. (2017){{< tbib '81' '387b7906-07c3-431f-a441-5a103220a974' >}} DP16 | Mengel et al. (2016){{< tbib '257' '94117a50-acc5-4dbf-8029-368aa3fc9680' >}} | |
| RCP8.5 (higher) | 21–38 (0.7–1.2) | 16–34 (0.5–1.1) | 17–48 (0.6–1.6) | 15–28 (0.5–0.9) |
| RCP4.5 (lower) | 18–35 (0.6–1.1) | 15–31 (0.5–1.0) | 14–43 (0.5–1.4) | 14–25 (0.5–0.8) |
| RCP2.6 (very low) | 18–33 (0.6–1.1) | 14–29 (0.5–1.0) | 12–41 (0.4–1.3) | 13–23 (0.4–0.8) |
| Kopp et al. (2014){{< tbib '77' '38924fa0-a0dd-44c9-a2a0-366ca610b280' >}} | Kopp et al. (2016){{< tbib '58' 'a0130167-b319-493d-bedc-7cab8f8fe9d9' >}} | Kopp et al. (2017){{< tbib '81' '387b7906-07c3-431f-a441-5a103220a974' >}} DP16 | Mengel et al. (2016){{< tbib '257' '94117a50-acc5-4dbf-8029-368aa3fc9680' >}} | |
| RCP8.5 (higher) | 55–121 (1.8–4.0) | 52–131 (1.7–4.3) | 93–243 (3.1–8.0) | 57–131 (1.9–4.3) |
| RCP4.5 (lower) | 36–93 (1.2–3.1) | 33–85 (1.1–2.8) | 50–158 (1.6–5.2) | 37–77 (1.2–2.5) |
| RCP2.6 (very low) | 29–82 (1.0–2.7) | 24–61 (0.8–2.0) | 26–98 (0.9–3.2) | 28–56 (0.9–1.8) |
This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Global average sea level has risen by about 7–8 inches (16–21 cm) since 1900, with almost half this rise occurring since 1993 as oceans have warmed and land-based ice has melted (very high confidence). Relative to the year 2000, sea level is very likely to rise 1 to 4 feet (0.3 to 1.3 m) by the end of the century (medium confidence). Emerging science regarding Antarctic ice sheet stability suggests that, for higher scenarios, a rise exceeding 8 feet (2.4 m) by 2100 is physically possible, although the probability of such an extreme outcome cannot currently be assessed.
' uncertainties: 'Uncertainties in reconstructed GMSL change relate to the sparsity of tide gauge records, particularly before the middle of the 20th century, and to different statistical approaches for estimating GMSL change from these sparse records. Uncertainties in reconstructed GMSL change before the twentieth century also relate to the sparsity of geological proxies for sea level change, the interpretation of these proxies, and the dating of these proxies. Uncertainty in attribution relates to the reconstruction of past changes and the magnitude of unforced variability.
Since NCA3, multiple different approaches have been used to generate probabilistic projections of GMSL rise, conditional upon the RCPs. These approaches are in general agreement. However, emerging results indicate that marine-based sectors of the Antarctic ice sheet are more unstable than previous modeling indicated. The rate of ice sheet mass changes remains challenging to project.
' uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-4 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is very high confidence in trends since 1895, based on the instrumental record, since this is a long-term record with measurements made with relatively high precision. There is high confidence for trends that are based on surface/satellite agreement since 1979, since this is a shorter record. There is medium confidence for trends based on paleoclimate data, as this is a long record but with relatively low precision.
There is very high confidence in observed changes in average annual and seasonal temperature and observed changes in temperature extremes over the United States, as these are based upon the convergence of evidence from multiple data sources, analyses, and assessments including the instrumental record.
There is high confidence that the range of projected changes in average temperature and temperature extremes over the United States encompasses the range of likely change, based upon the convergence of evidence from basic physics, multiple model simulations, analyses, and assessments.
' evidence: "The Key Message and supporting text summarize extensive evidence documented in the climate science literature. Similar statements about changes exist in other reports (e.g., NCA3,{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} Climate Change Impacts in the United States,{{< tbib '263' 'e251f590-177e-4ba6-8ed1-6f68b5e54c8a' >}} SAP 1.1: Temperature trends in the lower atmosphere).{{< tbib '264' 'f135add4-6d4c-4d88-a8f1-b880dbf5334f' >}}
Evidence for changes in U.S. climate arises from multiple analyses of data from in situ, satellite, and other records undertaken by many groups over several decades. The primary dataset for surface temperatures in the United States is nClimGrid,{{< tbib '85' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}},{{
Evidence for changes in U.S. climate arises from multiple analyses of in situ data using widely published climate extremes indices. For the analyses presented here, the source of in situ data is the Global Historical Climatology Network–Daily dataset.{{< tbib '268' '9b433446-b58f-4358-9737-5a6ccc2f6fcf' >}} Changes in extremes were assessed using long-term stations with minimal missing data to avoid network-induced variability on the long-term time series. Cold wave frequency was quantified using the Cold Spell Duration Index,{{< tbib '269' 'e6ecbe14-fe1b-46f8-bad5-bde9e4cc658a' >}} heat wave frequency was quantified using the Warm Spell Duration Index,{{< tbib '269' 'e6ecbe14-fe1b-46f8-bad5-bde9e4cc658a' >}} and heat wave intensity was quantified using the Heat Wave Magnitude Index Daily.{{< tbib '270' '546ef0fe-bfae-43ee-969e-5870c581e426' >}} Station-based index values were averaged into 4° grid boxes, which were then area-averaged into a time series for the contiguous United States. Note that a variety of other threshold and percentile-based indices were also evaluated, with consistent results (e.g., the Dust Bowl was consistently the peak period for extreme heat). Changes in record-setting temperatures were quantified, as in Meehl et al. (2016).{{< tbib '13' '72301197-e20a-4328-accb-4276341a25db' >}}
Projections are based on global model results and associated downscaled products from CMIP5 for a lower scenario (RCP4.5) and a higher scenario (RCP8.5). Model weighting is employed to refine projections for each RCP. Weighting parameters are based on model independence and skill over North America for seasonal temperature and annual extremes. The multimodel mean is based on 32 model projections that were statistically downscaled using the LOcalized Constructed Analogs technique.{{< tbib '247' '62c66ef3-cddb-4797-ba0e-5672fbcc27b3' >}} The range is defined as the difference between the average increase in the three coolest models and the average increase in the three warmest models. All increases are significant (i.e., more than 50% of the models show a statistically significant change, and more than 67% agree on the sign of the change).{{< tbib '271' 'b63c9720-f770-4718-89cc-53b3616e2bec' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/our-changing-climate/finding/key-message-2-5.yaml identifier: key-message-2-5 ordinal: 5 process: "This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Annual average temperature over the contiguous United States has increased by 1.2ºF (0.7°C) over the last few decades and by 1.8°F (1°C) relative to the beginning of the last century (very high confidence). Additional increases in annual average temperature of about 2.5°F (1.4°C) are expected over the next few decades regardless of future emissions, and increases ranging from 3°F to 12°F (1.6°–6.6°C) are expected by the end of century, depending on whether the world follows a higher or lower future scenario, with proportionally greater changes in high temperature extremes (high confidence).
' uncertainties: "The primary uncertainties for surface data relate to historical changes in station location, temperature instrumentation, observing practice, and spatial sampling (particularly in areas and periods with low station density, such as the intermountain West in the early 20th century). Much research has been done to account for these issues, resulting in techniques that make adjustments at the station level to improve the homogeneity of the time series (e.g., Easterling and Peterson 1995, Menne and Williams 2009{{< tbib '272' 'a7bd80fe-7df0-456b-9978-8f7e222bfafa' >}},{{
Global climate models are subject to structural and parametric uncertainty, resulting in a range of estimates of future changes in average temperature. This is partially mitigated through the use of model weighting and pattern scaling. Furthermore, virtually every ensemble member of every model projection contains an increase in temperature by mid- and late-century. Empirical downscaling introduces additional uncertainty (e.g., with respect to stationarity).
" uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-5 url: ~ - chapter_identifier: our-changing-climate confidence: "Confidence is medium that precipitation has increased and high that heavy precipitation events have increased in the United States. Furthermore, confidence is also high that the important regional and seasonal differences in changes documented here are robust.
Based on evidence from climate model simulations and our fundamental understanding of the relationship of water vapor to temperature, confidence is high that extreme precipitation will increase in all regions of the United States. However, based on the evidence and understanding of the issues leading to uncertainties, confidence is medium that more total precipitation is projected for the northern United States and less for the Southwest.
Based on the evidence and understanding of the issues leading to uncertainties, confidence is medium that average annual precipitation has increased in the United States. Furthermore, confidence is also medium that the important regional and seasonal differences in changes documented in the text and in Figure 7.1 in Easterling et al. (2017){{< tbib '94' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} are robust.
Given the evidence base and uncertainties, confidence is medium that snow cover extent has declined in the United States and medium that extreme snowfall years have declined in recent years. Confidence is high that western U.S. snowpack will decline in the future, and confidence is medium that a shift from snow domination to rain domination will occur in the parts of the central and eastern United States cited in the text, as well as that soil moisture in the surface (top 10cm) will decrease.
" evidence: "The Key Message and supporting text summarize extensive evidence documented in the climate science peer-reviewed literature and previous National Climate Assessments (e.g., Karl et al. 2009, Walsh et al. 2014{{< tbib '88' 'a6a312ba-6fd1-4006-9a60-45112db52190' >}},{{
Numerous papers have been written documenting observed changes in heavy precipitation events in the United States (e.g., Kunkel et al. 2003, Groisman et al. 2004{{< tbib '275' '642a65e4-fe5d-4655-97e1-49a8a9bfc297' >}},{{
Evidence of historical changes in snow cover extent and reduction in extreme snowfall years is consistent with our understanding of the climate system’s response to increasing greenhouse gases. Furthermore, climate models continue to consistently show future declines in snowpack in the western United States. Recent model projections for the eastern United States also confirm a future shift from snowfall to rainfall during the cold season in colder portions of the central and eastern United States. Each of these changes is documented in the peer-reviewed literature and cited in the main text of this chapter.
Evidence of future change in precipitation is based on climate model projections and our understanding of the climate system’s response to increasing greenhouse gases, and on regional mechanisms behind the projected changes. In particular, Figure 7.7 in Easterling et al. (2017){{< tbib '94' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} documents projected changes in the 20-year return period amount using the LOCA data, and Figure 7.6{{< tbib '94' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} shows changes in 2-day totals for the 5-year return period using the CMIP5 suite of models. Each figure shows robust changes in extreme precipitation events as they are defined in the figure. However, Figure 7.5{{< tbib '94' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} shows changes in seasonal and annual precipitation and shows where confidence in the changes is higher based on consistency between the models, and there are large areas where the projected change is uncertain.
" href: https://data.globalchange.gov/report/nca4/chapter/our-changing-climate/finding/key-message-2-6.yaml identifier: key-message-2-6 ordinal: 6 process: "This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Annual precipitation since the beginning of the last century has increased across most of the northern and eastern United States and decreased across much of the southern and western United States. Over the coming century, significant increases are projected in winter and spring over the Northern Great Plains, the Upper Midwest, and the Northeast (medium confidence). Observed increases in the frequency and intensity of heavy precipitation events in most parts of the United States are projected to continue (high confidence). Surface soil moisture over most of the United States is likely to decrease (medium confidence), accompanied by large declines in snowpack in the western United States (high confidence) and shifts to more winter precipitation falling as rain rather than snow (medium confidence).
' uncertainties: "The main issue that relates to uncertainty in historical trends is the sensitivity of observed precipitation trends to the spatial distribution of observing stations and to historical changes in station location, rain gauges, the local landscape, and observing practices. These issues are mitigated somewhat by new methods to produce spatial grids{{< tbib '152' '596a7f1e-6ce5-4bdf-b144-d0715a7567bd' >}} through time.
This includes the sensitivity of observed snow changes to the spatial distribution of observing stations and to historical changes in station location, rain gauges, and observing practices, particularly for snow. Future changes in the frequency and intensity of meteorological systems causing heavy snow are less certain than temperature changes.
A key issue is how well climate models simulate precipitation, which is one of the more challenging aspects of weather and climate simulation. In particular, comparisons of model projections for total precipitation (from both CMIP3 and CMIP5; see Sun et al. 2015{{< tbib '271' 'b63c9720-f770-4718-89cc-53b3616e2bec' >}}) by NCA3 region show a spread of responses in some regions (e.g., Southwest) such that they are opposite from the ensemble average response. The continental United States is positioned in the transition zone between expected drying in the subtropics and projected wetting in the mid- and higherlatitudes. There are some differences in the location of this transition between CMIP3 and CMIP5 models, and thus there remains uncertainty in the exact location of the transition zone.
" uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-6 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is very high confidence that the arctic surface and air temperatures have warmed across Alaska and the Arctic at a much faster rate than the global average is provided by the multiple datasets analyzed by multiple independent groups indicating the same conclusion. Additionally, climate models capture the enhanced warming in the Arctic, indicating a solid understanding of the underlying physical mechanisms.
There is high confidence that permafrost is thawing, becoming discontinuous, and releasing CO2 and CH4. Physically based arguments and observed increases in CO2 and CH4 emissions as permafrost thaws indicate that the feedback is positive. This confidence level is justified based on observations of rapidly changing permafrost characteristics.
There is very high confidence that arctic sea and land ice melt is accelerating and mountain glacier ice mass is declining, given the multiple observational sources and analysis techniques documented in the peer-reviewed climate science literature.
' evidence: "Annual average near-surface air temperatures across Alaska and the Arctic have increased over the last 50 years at a rate more than twice the global average. Observational studies using ground-based observing stations and satellites analyzed by multiple independent groups support this finding. The enhanced sensitivity of the arctic climate system to anthropogenic forcing is also supported by climate modeling evidence, indicating a solid grasp of the underlying physics. These multiple lines of evidence provide very high confidence of enhanced arctic warming with potentially significant impacts on coastal communities and marine ecosystems.
This aspect of the Key Message is supported by observational evidence from ground-based observing stations, satellites, and data model temperature analyses from multiple sources and independent analysis techniques.{{< tbib '117' 'e2086a52-de43-4628-97f8-05fb1c8e1e45' >}},{{
Permafrost is thawing, becoming more discontinuous, and releasing carbon dioxide (CO2) and methane (CH4). Observational and modeling evidence indicates that permafrost has thawed and released additional CO2 and CH4, indicating that the permafrost–carbon feedback is positive, accounting for additional warming of approximately 0.08ºC to 0.50ºC on top of climate model projections. Although the magnitude and timing of the permafrost–carbon feedback are uncertain due to a range of poorly understood processes (deep soil and ice wedge processes, plant carbon uptake, dependence of uptake and emissions on vegetation and soil type, and the role of rapid permafrost thaw processes such as thermokarst), emerging science and the newest estimates continue to indicate that this feedback is more likely on the larger side of the range. Impacts of permafrost thaw and the permafrost–carbon feedback complicate our ability to limit future temperature changes by adding a currently unconstrained radiative forcing to the climate system.
This part of the Key Message is supported by observational evidence of warming permafrost temperatures and a deepening active layer, in situ gas measurements, laboratory incubation experiments of CO2 and CH4 release, and model studies.{{< tbib '126' 'e787a738-62a2-4c16-984c-b37f225a7510' >}},{{
Arctic land and sea ice loss observed in the last three decades continues, in some cases accelerating. A diverse range of observational evidence from multiple data sources and independent analysis techniques provides consistent evidence of substantial declines in arctic sea ice extent, thickness, and volume since at least 1979, mountain glacier melt over the last 50 years, and accelerating mass loss from Greenland. An array of different models and independent analyses indicate that future declines in ice across the Arctic are expected, resulting in late summers in the Arctic very likely becoming ice free by mid-century.
This final aspect of the Key Message is supported by observational evidence from multiple ground-based and satellite-based observational techniques (including passive microwave, laser and radar altimetry, and gravimetry) analyzed by independent groups using different techniques reaching similar conclusions.{{< tbib '127' '3d339c60-bdf6-44f9-900d-249676925b4f' >}},{{
This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'In the Arctic, annual average temperatures have increased more than twice as fast as the global average, accompanied by thawing permafrost and loss of sea ice and glacier mass (very high confidence). Arctic-wide glacial and sea ice loss is expected to continue; by mid-century, it is very likely that the Arctic will be nearly free of sea ice in late summer (very high confidence). Permafrost is expected to continue to thaw over the coming century as well, and the carbon dioxide and methane released from thawing permafrost has the potential to amplify human-induced warming, possibly significantly (high confidence).
' uncertainties: 'The lack of high-quality data and the restricted spatial resolution of surface and ground temperature data over many arctic land regions, coupled with the fact that there are essentially no measurements over the Central Arctic Ocean, hampers the ability to better refine the rate of arctic warming and completely restricts our ability to quantify and detect regional trends, especially over the sea ice. Climate models generally produce an arctic warming between two to three times the global mean warming. A key uncertainty is our quantitative knowledge of the contributions from individual feedback processes in driving the accelerated arctic warming. Reducing this uncertainty will help constrain projections of future arctic warming.
A lack of observations affects not only the ability to detect trends but also to quantify a potentially significant positive feedback to climate warming: the permafrost–carbon feedback. Major uncertainties are related to deep soil and thermokarst processes, as well as the persistence or degradation of massive ice (e.g., ice wedges) and the dependence of CO2 and CH4 uptake and production on vegetation and soil properties. Uncertainties also exist in relevant soil processes during and after permafrost thaw, especially those that control unfrozen soil carbon storage and plant carbon uptake and net ecosystem exchange. Many processes with the potential to drive rapid permafrost thaw (such as thermokarst) are not included in current Earth System Models.
Key uncertainties remain in the quantification and modeling of key physical processes that contribute to the acceleration of land and sea ice melting. Climate models are unable to capture the rapid pace of observed sea and land ice melt over the last 15 years; a major factor is our inability to quantify and accurately model the physical processes driving the accelerated melting. The interactions between atmospheric circulation, ice dynamics and thermodynamics, clouds, and specifically the influence on the surface energy budget are key uncertainties. Mechanisms controlling marine-terminating glacier dynamics, specifically the roles of atmospheric warming, seawater intrusions under floating ice shelves, and the penetration of surface meltwater to the glacier bed, are key uncertainties in projecting Greenland ice sheet melt.
' uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-7 url: ~ - chapter_identifier: our-changing-climate confidence: 'There is medium to high confidence that the tropics and related features of the global circulation have expanded poleward is based upon the results of a large number of observational studies, using a wide variety of metrics and datasets, which reach similar conclusions. A large number of studies utilizing modeling of different complexity and theoretical considerations provide compounding evidence that human activities like increases in greenhouse gases, ozone depletion, and anthropogenic aerosols contributed to the observed poleward expansion of the tropics. Climate models forced with these anthropogenic drivers cannot explain the observed magnitude of tropical expansion, and some studies suggest a possibly large contribution of internal variability. These multiple lines of evidence lead to the conclusion of medium confidence that human activities contributed to observed expansion of the tropics.
Confidence is rated as high in tropical cyclone rainfall projections and medium in intensity projections since there are a number of publications supporting these overall conclusions, fairly well-established theory, general consistency among different studies, varying methods used in studies, and still a fairly strong consensus among studies. However, a limiting factor for confidence in the results is the lack of a supporting detectable anthropogenic contribution in observed tropical cyclone data.
There is low to medium confidence for increased occurrence of the most intense tropical cyclones for most basins, as there are relatively few formal studies focused on these changes, and the change in occurrence of such storms would be enhanced by increased intensities but reduced by decreased overall frequency of tropical cyclones.
Confidence in this finding on atmospheric rivers is rated as medium based on qualitatively similar projections among different studies.
' evidence: "The tropics have expanded poleward in each hemisphere over the period 1979–2009 (medium to high confidence) as shown by a large number of studies using a variety of metrics, observations, and reanalysis. Modeling studies and theoretical considerations illustrate that human activities like increases in greenhouse gases, ozone depletion, and anthropogenic aerosols cause a widening of the tropics. There is medium confidence that human activities have contributed to the observed poleward expansion, taking into account uncertainties in the magnitude of observed trends and a possible large contribution of natural climate variability.
The first part of the Key Message is supported by statements of the previous international IPCC AR5 assessment{{< tbib '120' '47a5196b-4fba-4fdb-8647-8945627725bb' >}} and a large number of more recent studies that examined the magnitude of the observed tropical widening and various causes.{{< tbib '95' 'a80ce47f-ac9a-43d2-9179-acad0e28e05a' >}},{{
Models are generally in agreement that tropical cyclones will be more intense and have higher precipitation rates, at least in most basins. Given the agreement among models and support of theory and mechanistic understanding, there is medium to high confidence in the overall projection, although there is some limitation on confidence levels due to the lack of a supporting detectable anthropogenic contribution to tropical cyclone intensities or precipitation rates.
The second part of the Key Message is also based on extensive evidence documented in the climate science literature and is similar to statements made in previous national (NCA3){{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} and international{{< tbib '249' 'f03117be-ccfe-4f88-b70a-ffd4351b8190' >}} assessments. Since these assessments, more recent downscaling studies have further supported these assessments (e.g., Knutson et al. 2015{{< tbib '170' '4f1e7aa1-0c36-4220-ac77-7d55bcb33061' >}}), though pointing out that the changes (future increased intensity and tropical cyclone precipitation rates) may not occur in all basins.
Increases in atmospheric river frequency and intensity are expected along the U.S. West Coast, leading to the likelihood of more frequent flooding conditions, with uncertainties remaining in the details of the spatial structure of these systems along the coast (for example, northern vs. southern California). Evidence for the expectation of an increase in the frequency and severity of landfalling atmospheric rivers on the U.S. West Coast comes from the CMIP-based climate change projection studies of Dettinger (2011).{{< tbib '163' '67ee7e56-b6a2-4ada-a7e8-ff836b1c58d1' >}} Warner et al. (2015),{{< tbib '164' '40ffbbdf-74f1-4511-b1f1-a2b2a165185e' >}} Payne and Magnusdottir (2015),{{< tbib '312' 'd13ddcaa-9080-4fab-9514-c45365ed3740' >}} Gao et al. (2015),{{< tbib '165' '60ce531d-0064-4170-8b4d-e63bbb9f0c67' >}} Radić et al. (2015),{{< tbib '313' '8927a54e-415e-4af2-aeb8-665cfe2d17ee' >}} and Hagos et al. (2016).{{< tbib '314' 'a2470cdb-4b8f-4ed6-8c5f-38cd301053a2' >}} The close connection between atmospheric rivers and water availability and flooding is based on the present-day observation studies of Guan et al. (2010),{{< tbib '315' '59dfa0b2-2e94-4eb9-89fd-3adbbd1d61d4' >}} Dettinger (2011),{{< tbib '163' '67ee7e56-b6a2-4ada-a7e8-ff836b1c58d1' >}} Ralph et al. (2006),{{< tbib '316' '8caee927-3ee1-4084-a42e-e9487f4ebedf' >}} Neiman et al. (2011),{{< tbib '317' 'a73e96c6-679f-4f76-a749-571f43601e5c' >}} Moore et al. (2012),{{< tbib '318' 'ad8a08da-1ddc-452c-ac17-a5208fa4fe09' >}} and Dettinger (2013).{{< tbib '319' '84acc46e-9dcf-43e7-8acc-07f07167ee8e' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/our-changing-climate/finding/key-message-2-8.yaml identifier: key-message-2-8 ordinal: 8 process: "This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Human-induced change is affecting atmospheric dynamics and contributing to the poleward expansion of the tropics and the northward shift in Northern Hemisphere winter storm tracks since the 1950s (medium to high confidence). Increases in greenhouse gases and decreases in air pollution have contributed to increases in Atlantic hurricane activity since 1970 (medium confidence). In the future, Atlantic and eastern North Pacific hurricane rainfall (high confidence) and intensity (medium confidence) are projected to increase, as are the frequency and severity of landfalling “atmospheric rivers” on the West Coast (medium confidence).
' uncertainties: "The rate of observed expansion of the tropics depends on which metric is used.{{< tbib '161' '798360ca-4177-462c-991a-c7a512d9287c' >}} The linkages between different metrics are not fully explored. Uncertainties also result from the utilization of reanalysis to determine trends and from limited observational records of free atmosphere circulation, precipitation, and evaporation. The dynamical mechanisms behind changes in the width of the tropical belt (e.g., tropical–extratropical interactions, baroclinic eddies) are not fully understood. There is also a limited understanding of how various climate forcings, such as anthropogenic aerosols, affect the width of the tropics. The coarse horizontal and vertical resolution of global climate models may limit the ability of these models to properly resolve latitudinal changes in the atmospheric circulation. Limited observational records affect the ability to accurately estimate the contribution of natural decadal to multi-decadal variability on observed expansion of the tropics.
A key uncertainty in tropical cyclones (TCs) is the lack of a supporting detectable anthropogenic signal in the historical data to add further confidence to these projections. As such, confidence in the projections is based on agreement among different modeling studies and physical understanding (for example, potential intensity theory for TC intensities and the expectation of stronger moisture convergence, and thus higher precipitation rates, in TCs in a warmer environment containing greater amounts of environmental atmospheric moisture). Additional uncertainty stems from uncertainty in both the projected pattern and magnitude of future SST.{{< tbib '170' '4f1e7aa1-0c36-4220-ac77-7d55bcb33061' >}}
In terms of atmospheric rivers (ARs), a modest uncertainty remains in the lack of a supporting detectable anthropogenic signal in the historical data to add further confidence to these projections. However, the overall increase in ARs projected/expected is based to a very large degree on very high confidence that the atmospheric water vapor will increase. Thus, increasing water vapor coupled with little projected change in wind structure/intensity still indicates increases in the frequency/intensity of ARs. A modest uncertainty arises in quantifying the expected change at a regional level (for example, northern Oregon versus southern Oregon), given that there are some changes expected in the position of the jet stream that might influence the degree of increase for different locations along the west coast. Uncertainty in the projections of the number and intensity of ARs is introduced by uncertainties in the models’ ability to represent ARs and their interactions with climate.
" uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-8 url: ~ - chapter_identifier: our-changing-climate confidence: 'Because of the enumerated physical processes, there is very high confidence that RSL change will vary across U.S. coastlines. There is high confidence in the likely differences of RSL change from GMSL change under different levels of GMSL change, based on projections incorporating the different relevant processes. There is low confidence that the flood risk at specific locations will be amplified from a major tropical storm this century.
' evidence: "The part of the Key Message regarding the existence of geographic variability is based upon a broader observational, modeling, and theoretical literature. The specific differences are based upon the scenarios described by the Federal Interagency Sea Level Rise Task Force.{{< tbib '76' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} The processes that cause geographic variability in regional sea level (RSL) change are also reviewed by Kopp et al. (2015).{{< tbib '320' 'e8f60819-839e-4772-8a49-7c57d9c53424' >}} Long tide gauge datasets reveal where RSL rise is largely driven by vertical land motion due to glacio-isostatic adjustment and fluid withdrawal along many U.S. coastlines.{{< tbib '321' 'ab69428a-34a4-412f-8c85-b3bb8043509c' >}},{{
The frequency, extent, and depth of extreme event-driven (e.g., 5- to 100-year event probabilities) coastal flooding relative to existing infrastructure will continue to increase in the future as local RSL rises.{{< tbib '57' '3bae2310-7572-47e2-99a4-9e4276764934' >}},{{
This chapter is based on the collective effort of 32 authors, 3 review editors, and 18 contributing authors comprising the writing team for the Climate Science Special Report (CSSR),{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} a featured U.S. Global Change Research Project (USGCRP) deliverable and Volume I of the Fourth National Climate Assessment (NCA4). An open call for technical contributors took place in March 2016, and a federal science steering committee appointed the CSSR team. CSSR underwent three rounds of technical federal review, external peer review by the National Academies of Sciences, Engineering, and Medicine, and a review that was open to public comment. Three in-person Lead Authors Meetings were conducted at various stages of the development cycle to evaluate comments received, assign drafting responsibilities, and ensure cross-chapter coordination and consistency in capturing the state of climate science in the United States. In October 2016, an 11-member core writing team was tasked with capturing the most important CSSR key findings and generating an Executive Summary. The final draft of this summary and the underlying chapters was compiled in June 2017.
The NCA4 Chapter 2 author team was pulled exclusively from CSSR experts tasked with leading chapters and/or serving on the Executive Summary core writing team, thus representing a comprehensive cross-section of climate science disciplines and supplying the breadth necessary to synthesize CSSR content. NCA4 Chapter 2 authors are leading experts in climate science trends and projections, detection and attribution, temperature and precipitation change, severe weather and extreme events, sea level rise and ocean processes, mitigation, and risk analysis. The chapter was developed through technical discussions first promulgated by the literature assessments, prior efforts of USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} e-mail exchanges, and phone consultations conducted to craft this chapter and subsequent deliberations via phone and e-mail exchanges to hone content for the current application. The team placed particular emphasis on the state of science, what was covered in USGCRP,{{< tbib '208' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and what is new since the release of the Third NCA in 2014.{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}}
" report_identifier: nca4 statement: 'Regional changes in sea level rise and coastal flooding are not evenly distributed across the United States; ocean circulation changes, sinking land, and Antarctic ice melt will result in greater-than-average sea level rise for the Northeast and western Gulf of Mexico under lower scenarios and most of the U.S. coastline other than Alaska under higher scenarios (very high confidence). Since the 1960s, sea level rise has already increased the frequency of high tide flooding by a factor of 5 to 10 for several U.S. coastal communities. The frequency, depth, and extent of tidal flooding is expected to continue to increase in the future (high confidence), as is the more severe flooding associated with coastal storms, such as hurricanes and nor’easters (low confidence).
' uncertainties: "Since NCA3,{{< tbib '1' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} multiple authors have produced global or regional studies synthesizing the major process that causes global and local sea level change to diverge. The largest sources of uncertainty in the geographic variability of sea level change are ocean dynamic sea level change and, for those regions where sea level fingerprints for Greenland and Antarctica differ from the global mean in different directions, the relative contributions of these two sources to projected sea level change.
Uncertainties remain large with respect to the precise change in future risk of a major coastal impact at a specific location from changes in the most intense tropical cyclone characteristics and tracks beyond changes imposed from local sea level rise.
" uri: /report/nca4/chapter/our-changing-climate/finding/key-message-2-9 url: ~ - chapter_identifier: us-caribbean confidence: 'There is high confidence that freshwater availability will likely be constrained by the end of the century and medium confidence that extreme rainfall events will likely increase in intensity. There is high confidence that sea level rise will very likely cause saltwater intrusion impacts on coastal freshwater aquifers. There is medium confidence about likely changes to ecological life zones but low confidence about the distributional effects on the existing terrestrial ecosystems in the region.
' evidence: "The average global atmospheric carbon dioxide (CO2) concentration has increased from 378 parts per million (ppm) in 2005 to over 406 ppm during April of 2017. The rate of increase over this period appears to be constant, and there is no indication that the rate will decrease in the future.{{< tbib '146' '0b94246c-91be-4f95-ae61-d36fdf775ff3' >}} Several climate change studies have concluded that owing to increased atmospheric CO2 and the consequent global climate change, rainfall will likely decrease in the region between now and the end of the century (e.g., Meehl et al. 2007, Biasutti et al. 2012, Campbell et al. 2011, Cashman et al. 2010{{< tbib '2' '03abb6ea-0525-4fac-a321-121ca0727673' >}},{{
Streamflow is estimated using hydrologic models that are calibrated to networks of stream gauges and precipitation measurements. Reservoirs are considered in a permanent supply deficit if the annual streamflow leaving these reservoirs falls below zero after estimating withdrawals for human consumption, evapotranspiration, and rainfall. Projections of when deficit conditions could occur (circa 2025) are estimated using climate models.{{< tbib '46' 'a045f06c-0964-4286-9b5a-9b625da4eb2d' >}}
Saltwater intrusion associated with sea level rise will reduce the quantity and quality of freshwater in coastal aquifers. In Puerto Rico, groundwater quality can change when the water table is below sea level in coastal areas or when the intensity of pumping induces local upconing of deeper, poor-quality water.{{< tbib '43' '553e2d0a-c0ad-4540-9c5f-1f47374129ec' >}} Upconing is the process by which saline water underlying freshwater in an aquifer rises upward into the freshwater zone due to pumping.{{< tbib '150' '4375edd4-4f85-4a9f-bf62-37c2985ade2b' >}} When the water table is below sea level, the natural discharge of groundwater along the coast is reversed and can result in the inland movement of seawater or the upconing of low-quality water.{{< tbib '151' '1b555f67-0af6-4f16-882b-0c253117b9c8' >}},{{
The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.
Freshwater is critical to life throughout the Caribbean. Increasing global carbon emissions are projected to reduce average rainfall in this region by the end of the century (likely, high confidence), constraining freshwater availability, while extreme rainfall events, which can increase freshwater flooding impacts, are expected to increase in intensity (likely, medium confidence). Saltwater intrusion associated with sea level rise will reduce the quantity and quality of freshwater in coastal aquifers (very likely, high confidence). Increasing variability in rainfall events and increasing temperatures will likely alter the distribution of ecological life zones and exacerbate existing problems in water management, planning, and infrastructure capacity (likely, medium confidence).
' uncertainties: "As global changes continue to alter the hydrological cycle across the region, water resources are expected to be affected in both quantity and quality. There is still uncertainty as to the extent and severity of these global changes on small island nations such as Puerto Rico and the USVI, despite notable advancements in downscaled modeling exercises. Current climatological observations have presented an overall increase in mean annual precipitation across Puerto Rico.{{< tbib '153' '0049e302-7751-4977-91ff-0df54d0ab326' >}} However, climate model projections point toward an overall decrease in annual mean precipitation toward 2050 and an increase in rainfall intensity for extreme rainfall,{{< tbib '6' '72d1011e-bdff-49c0-b00f-8222c2a350ea' >}},{{
Selected CMIP3 (Coupled Model Intercomparison Project, phase 3) and CMIP5 global climate models (GCMs) capture the general large-scale atmospheric circulation that controls seasonal rainfall patterns within the Caribbean{{< tbib '155' '5d493a0a-db95-418d-ad99-148d753db96a' >}} and provide justification that these GCM projections can be further downscaled to capture important rainfall characteristics associated with the islands.{{< tbib '156' 'e16c77ed-0eaf-4fa6-8c98-256a28794b3b' >}} Systemic dry biases exist, however, in the GCMs.{{< tbib '155' '5d493a0a-db95-418d-ad99-148d753db96a' >}} And many GCMs fail to capture the bimodal precipitation pattern in the region.{{< tbib '28' '56d77153-c8fc-4fcf-a7f0-fa0e843936f1' >}} The CMIP3 generation of GCMs that do capture the bimodal rainfall pattern predict extreme drying at the middle and end of this century.{{< tbib '7' '650b2907-85b1-4b76-a339-a9ec1703c5bd' >}},{{
There is high confidence that increasing ocean temperatures, changes in ocean acidity, and changes in the frequency and intensity of storms are extremely likely to affect coastal and marine resources. Large storm events within the past decade have resulted in significant effects on marine resources, particularly coral habitats and organisms that rely on them. There is medium confidence in predictions that coral habitats will likely continue to decline throughout the Caribbean, with associated effects on resources dependent on these habitats; although, scientific studies are still needed in terms of climate change effects on fisheries resources, particularly for species that are found in offshore waters or are pelagic. Changes in coral habitats are already occurring as evidenced by massive coral bleaching events (including a three-year global-level bleaching event from 2015–2017) and the increase in these events. Such changes in bleaching events are due to rising sea surface temperatures. There is high confidence that there have been changes in ocean pH and medium confidence on the ecological effects. Due to the lack of studies on the social consequences of climate change and associated losses of resources such as fisheries, there is medium confidence that effects on coastal and marine resources resulting from climate change will affect island economies. These effects can be a result of changes in availability and condition of fishery resources, loss of reefs and other coral communities that serve as coastal barriers, and effects on tourism due to loss of the resources that are primary attractions for visitors.
There is medium confidence in the ecological effects that will result due to changes in ocean pH. The CO2 system of seawater is well understood and established. As such, the understanding of the basic equilibria governing the process of ocean acidification dates back to at least 1960{{< tbib '168' 'b20e8c2b-cfb8-48b6-85c6-c981c361e267' >}} and represents a foundational understanding of modern chemical oceanography. The ecological consequences of human-induced changes to the system (that is, ocean acidification) is, however, a considerably new field. Both themes were assessed considering recent findings and based on adequate observed local data (for example, atmospheric pCO2 [carbon dioxide partial pressure] values are based on measurements of weekly air samples from St. Croix, the USVI, the United States, and Ragged Point, Barbados), complemented with empirical models. Projected changes in climate for the Caribbean islands were based on the future projections of fossil fuel emissions driven by reasonable models from the Intergovernmental Panel on Climate Change (IPCC).{{< tbib '169' 'bc140b4c-c2d9-4d99-a684-5c054dc5134f' >}} Additional empirical species response data would be useful for increasing the understanding of expected effects of ocean acidification on species and habitats in the Caribbean.
" evidence: "In 2006, the National Marine Fisheries Service (NMFS) listed elkhorn and staghorn corals as threatened species under the Endangered Species Act, with persistent elevated sea surface temperatures and sea level rise being two of the key factors influencing the listing decision.{{< tbib '158' '9d974b61-97ea-4778-977d-26701052c8e9' >}} The Acropora Biological Review Team (2005) found that the number of hurricanes affecting reef ecosystems in the Caribbean has increased over the past two decades (2 hurricanes in the 1970s, 6 in the 1980s, and 12 in the 1990s). Sea surface temperature is expected to continue rising, and this implies an increasing threat to elkhorn and staghorn corals from bleaching-induced mortality and possibly an exacerbation of disease effects. In 2014, NMFS listed an additional 5 species of Atlantic/Caribbean corals (lobed, mountainous star, boulder star, pillar, and rough cactus) as threatened and reevaluated the listing of elkhorn and staghorn corals, confirming them as threatened species; it also listed 15 Indo-Pacific coral species as threatened,{{< tbib '159' '8960de56-9b32-4544-9255-046a9ef45e0d' >}} with two of the key factors being ocean warming and ocean acidification. Brainard et al.{{< tbib '159' '8960de56-9b32-4544-9255-046a9ef45e0d' >}} found that ocean warming and related effects of climate change have already created a clear and present threat to many corals that will likely continue into the future and can be assessed with certainty out to 2100. Increases in human population densities and activity levels in the coastal zone are expected to continue, meaning the vulnerability of these populations and infrastructure will likely continue increasing with climate change.{{< tbib '160' '895e2c92-d614-4154-8509-7689918c8697' >}} Direct measurements at the Bermuda Atlantic Time-series Study station shows that surface ocean acidity has increased by about 12% and aragonite saturation (Ωarg) has decreased by about 8% over the past three decades.{{< tbib '161' 'ade3d353-6612-4e45-96d3-9269de56eda0' >}} These values agreed with those reported across the Caribbean{{< tbib '162' '0e312df5-ad3d-4709-8b58-8cea86d26415' >}} and Atlantic regions{{< tbib '18' 'd51156cc-0034-4afc-b2b7-1ad99efde458' >}},{{
Many coastal regions already experience low surface seawater pH and Ωarg conditions (localized or coastal ocean acidification) due to processes other than CO2 uptake. As a result, the effect of ocean acidification on coastal zones can be several times higher and faster than typically expected for oceanic waters.{{< tbib '163' 'dc5e5365-8b0f-4a21-93b4-c6a822be824d' >}}
Caribbean coral reefs in the Bahamas, Belize, Bonaire, and Grand Cayman are already experiencing significant reductions in carbonate production rates, with 37% of surveyed sites showing net erosion.{{< tbib '164' '0841a7ce-1022-4cf7-be4f-5c20d3b19f2a' >}} Friedrich et al. (2012).{{< tbib '66' 'a03f3916-2084-4353-bce4-adac93801617' >}} concluded that calcification rates may have already dropped by about 15% within the Caribbean with respect to their preindustrial values.
" href: https://data.globalchange.gov/report/nca4/chapter/us-caribbean/finding/key-message-20-2.yaml identifier: key-message-20-2 ordinal: 2 process: 'The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.
Marine ecological systems provide key ecosystem services such as commercial and recreational fisheries and coastal protection. These systems are threatened by changes in ocean surface temperature, ocean acidification, sea level rise, and changes in the frequency and intensity of storm events. Degradation of coral and other marine habitats can result in changes in the distribution of species that use these habitats and the loss of live coral cover, sponges, and other key species (very likely, high confidence). These changes will likely disrupt valuable ecosystem services, producing subsequent effects on Caribbean island economies (likely, medium confidence).
' uncertainties: "The link between climate stressors such as increasing sea surface temperatures and bleaching response and increasing prevalence of disease in corals is postulated. There is some scientific evidence indicating a link, but it is hard to make definitive conclusions. Effects of climate change on fisheries in the Caribbean have not been as well studied as the effects on marine habitats, particularly coral reefs.{{< tbib '74' '94f95306-0dd9-43cf-8e70-9a379423f31d' >}},{{
Uncertainty with respect to ocean acidification is dominated by uncertainty about how ecosystems and organisms will respond, particularly due to multiple interactions with other stressors.
The value of the loss of ecosystem services to ocean acidification is unknown. Such losses are attributable to the degradation of ecosystems that support important economic marine species such as coral, conch, oysters, fish larvae, urchins, and pelagic fish in the Caribbean. There is strong evidence for decreasing carbonate production, calcification rates, coral cover, and biomass of major reef-building species throughout the Caribbean region. However, there is still not enough evidence to conclude that all these decreased ecosystem processes are due to ocean acidification.
There are only a few studies on ecosystem and organism responses to climate stressors (such as ocean warming) that consider ocean acidification in the Caribbean. For instance, low pH values could affect nursery areas of commercially important species such as tuna, presenting a source of vulnerability for the economy, but studies are scarce. Ocean acidification could also affect the food web dynamics at lower trophic levels and have physiological effects at larval stages that would likely cascade upward, affecting coral and fish recruitment.
The effects of ocean acidification on coral reefs, shellfish, fish, and marine mammals will likely cause an economic effect on fisheries, coastal protection, and tourism in the Caribbean. Ocean acidification can exacerbate the current global warming effects on coral reefs, and it will likely continue deteriorating reef conditions and cause ecological regime shifts from coral to algal reefs.{{< tbib '77' 'b09adbe5-6a17-4d3c-ab96-b3d9e306af67' >}},{{
Sea level rise is currently the most immediate and well-understood climate-related threat to mangroves.{{< tbib '70' 'c527429c-5661-477a-a6f4-1690355bcbd5' >}} It is not clear how mangroves will respond to elevated CO2, and some studies suggest increases may actually be beneficial to mangroves.{{< tbib '70' 'c527429c-5661-477a-a6f4-1690355bcbd5' >}} Similarly, in the Caribbean where temperatures are already high, increasing temperatures, as well as declines in rainfall and corresponding increases in soil salinity during periods of drought, will likely increase plant water stress and reduce productivity. There have been limited studies on the effects of climate change on seagrass beds; therefore, these effects remain uncertain.{{< tbib '69' '63aac7f9-5e82-4aff-ab62-75c12537612f' >}} Sea level rise that results in reduced sunlight due to increased water depths can lead to the loss of seagrass beds from deeper waters. As discussed previously, the loss or degradation of these habitats, which are part of the coral reef ecosystem and serve as nursery habitat for important nursery species, will likely contribute to declines in fishery productivity due to climate change.
" uri: /report/nca4/chapter/us-caribbean/finding/key-message-20-2 url: ~ - chapter_identifier: us-caribbean confidence: 'Sea levels have already risen and will likely continue to rise in the future. Based on current levels of greenhouse gas emissions, glacial melt, and ice sheet loss, there is high confidence and likelihood in these sea level rise projections.
' evidence: "The Key Message and subsequent narrative text are based on the best available information for the U.S. Caribbean. There are not many studies on or projections for sea level rise for the U.S. Caribbean. Therefore, evidence of sea level rise used for this report comes from the U.S. Army Corps of Engineers’ (USACE) Sea Level Change Curve Calculator.{{< tbib '95' 'b46d7ec8-76b0-4469-bc00-9348475efd0f' >}} To calculate the Intermediate and High scenarios, the USACE uses modified National Research Council (NRC) curves, the most recent IPCC projections, and modified NRC projections with local rate of vertical land movement.{{< tbib '95' 'b46d7ec8-76b0-4469-bc00-9348475efd0f' >}} The four NOAA estimates integrate data ranging from tide gauge records for the lowest scenario to projected ocean warming from the IPCC’s global sea level rise projections combined with the maximum projection for glacier and ice sheet loss for 2100 for the highest scenario. The sea level rise analysis mainly focuses on data from two tide gauges chosen to be representative of the region, one in San Juan, Puerto Rico, and the other in Charlotte Amalie, USVI. There are two others in the region that provide sea level trend data located in Magueyes, Puerto Rico, and Lime Tree Bay, USVI.
Additional evidence that sea level is rising is well documented in Chapter 9: Oceans and in the Climate Science Special Report. There are also numerous empirical examples of sea level rise and its effects in Puerto Rico and the USVI, where beaches have been reduced by erosion, roads have been lost, and access to schools has been affected.
" href: https://data.globalchange.gov/report/nca4/chapter/us-caribbean/finding/key-message-20-3.yaml identifier: key-message-20-3 ordinal: 3 process: 'The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.
Coasts are a central feature of Caribbean island communities. Coastal zones dominate island economies and are home to critical infrastructure, public and private property, cultural heritage, and natural ecological systems. Sea level rise, combined with stronger wave action and higher storm surges, will worsen coastal flooding and increase coastal erosion (very likely, very high confidence), likely leading to diminished beach area (likely, high confidence), loss of storm surge barriers (likely, high confidence), decreased tourism (likely, medium confidence), and negative effects on livelihoods and well-being (likely, medium confidence). Adaptive planning and nature-based strategies, combined with active community participation and traditional knowledge, are beginning to be deployed to reduce the risks of a changing climate.
' uncertainties: 'Sea level rise is already occurring. However, the uncertainty lies in how much of an increase will take place in the future and how coastal social and ecological systems will respond. There are various models and projections to estimate this number, but it is influenced by many unknown factors, such as the amount of future greenhouse gas emissions and how quickly glaciers and ice sheets melt. Another major uncertainty lies in humans’ abilities to combat or adapt to these changes. The scale at which people and cities will be affected depends on the actions taken to reduce risk. Lastly, the experience of sea level rise on each coast and community is different, depending on land subsidence or accretion, land use, and erosion; thus, the severity of effects might differ based on these factors.
Due to the levels of uncertainty surrounding the projections, we focused much attention on the highest scenarios, as fewer consequences exist for planning in terms of the higher scenario (RCP8.5).
' uri: /report/nca4/chapter/us-caribbean/finding/key-message-20-3 url: ~ - chapter_identifier: us-caribbean confidence: 'There is high confidence that increasing temperatures threaten the health and well-being of people living in the U.S. Caribbean, especially in high-density urban areas where the UHI effect places further stress on city populations.
' evidence: 'In warm tropical areas like Puerto Rico and the USVI, higher summertime temperatures mean more energy is needed to cool buildings and homes, increasing the demand for energy. Heat episodes are becoming more common worldwide, including in tropical regions like the U.S. Caribbean. Higher frequency, duration, and intensity of heat episodes are triggering serious public health issues in San Juan. Heat poses a greater threat to health and well-being in high-density urban areas. Land use and land cover have affected local climate directly and indirectly, facilitating the urban heat island (UHI) effect, with potential effects on heat-related morbidity and mortality among urban populations.
' href: https://data.globalchange.gov/report/nca4/chapter/us-caribbean/finding/key-message-20-4.yaml identifier: key-message-20-4 ordinal: 4 process: 'The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.
Natural and social systems adapt to the temperatures under which they evolve and operate. Changes to average and extreme temperatures have direct and indirect effects on organisms and strong interactions with hydrological cycles, resulting in a variety of impacts. Continued increases in average temperatures will likely lead to decreases in agricultural productivity, changes in habitats and wildlife distributions, and risks to human health, especially in vulnerable populations. As maximum and minimum temperatures increase, there are likely to be fewer cool nights and more frequent hot days, which will likely affect the quality of life in the U.S. Caribbean. (High Confidence)
' uncertainties: "Warming is evident. A remaining scientific question is how ecological and social systems that have established themselves in a particular location can adapt to higher average temperatures.{{< tbib '170' 'fd10f97c-39c6-4f3a-8306-aead1a368908' >}} Islands such as Puerto Rico are particularly vulnerable because of heat events associated with changes in both terrestrial and marine conditions. Although there is evidence suggesting that mortality relative to risk increases in San Juan due to extreme heat,{{< tbib '12' 'cb5c02d3-6e9e-4dc5-8eaa-b87f57030bbf' >}} this association is not completely understood on tropical islands like Puerto Rico and the USVI. Addressing such hazards can benefit from new strategies that seek to determine linkages between human health, rapid and synoptic environmental monitoring, and the research that helps improve the forecast of hazardous conditions for particular human population segments or for other organisms.
" uri: /report/nca4/chapter/us-caribbean/finding/key-message-20-4 url: ~ - chapter_identifier: us-caribbean confidence: 'There is high confidence that increasing frequency of extreme events threatens life, property, and economy in the region, given that the U.S. Caribbean’s vulnerable populations and fragile economies are continually exposed to climate extremes. There is medium confidence that the frequency and intensity of the most extreme hurricanes and droughts will likely increase. There is high confidence that extreme events will likely continue to affect human health and well-being, economic development and tourism, conservation, agriculture, and danger from flooding. There is high confidence that future recovery and cultural continuity will depend on significant and integrated resilience planning across the region, focusing on collaborative actions among stakeholders.
' evidence: "On both Puerto Rico and the USVI, disaster events have caused billions of dollars in property and crop damages.{{< tbib '171' 'cdbb39c1-4de9-4067-8ebc-24de32b50b57' >}} Over the years, disaster-induced casualties have declined in both territories. Tropical cyclones, particularly hurricanes, continue to generate the most severe economic damage across the U.S. Caribbean. Floods and droughts are challenging to manage for both territories, and these challenges may be exacerbated by climate change induced shifts in precipitation regimes.
Climate modeling for tropical cyclone activity in the Atlantic Basin, including the Caribbean region, points toward an increase in the frequency of more intense hurricanes.{{< tbib '135' '349482df-4a77-4802-8b39-14d5e63b946f' >}} An increase in days with more than 3 inches of rain per 24-hour period is projected for Puerto Rico, based on statistically downscaled CMIP3 climate models.{{< tbib '28' '56d77153-c8fc-4fcf-a7f0-fa0e843936f1' >}} Changes in precipitation patterns are expected for Puerto Rico in the periods 2030–2050 and 2100, pointing toward an overall decrease in mean precipitation for different climate change scenarios.{{< tbib '7' '650b2907-85b1-4b76-a339-a9ec1703c5bd' >}},{{
While continental droughts typically affect vast regions, droughts affecting Puerto Rico and the USVI tend to vary significantly in extent and severity over smaller distances.{{< tbib '132' 'edd9a004-f859-41ae-9f93-80201c4ffd65' >}} Statistically downscaled climate projections for Puerto Rico suggest an increase of drought intensity (measured as the total annual dry days) and extremes (measured as the annual maximum number of consecutive dry days) due to an increase in mean and extreme temperatures and a decrease in precipitation.{{< tbib '7' '650b2907-85b1-4b76-a339-a9ec1703c5bd' >}}
An increase in mean atmospheric temperature has been observed across the U.S. Caribbean islands, particularly on Puerto Rico. An analysis of the observed temperatures across several NOAA weather stations in Puerto Rico showed rising temperature trends between 1970 and 2016.{{< tbib '172' 'e8d32931-3301-45c8-bfe7-b8e8b9fff6b6' >}} Following the principles established by the international Expert Team on Climate Change Detection and Indices,{{< tbib '173' 'e6ecbe14-fe1b-46f8-bad5-bde9e4cc658a' >}} temperature extremes and trends were identified, indicating significant increases in rising annual temperatures and an increase in extreme heat episodes.
" href: https://data.globalchange.gov/report/nca4/chapter/us-caribbean/finding/key-message-20-5.yaml identifier: key-message-20-5 ordinal: 5 process: 'The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.
Extreme events pose significant risks to life, property, and economy in the Caribbean, and some extreme events, such as flooding and droughts, are projected to increase in frequency and intensity (flooding as likely as not, medium confidence; droughts very likely, medium confidence). Increasing hurricane intensity and associated rainfall rates (likely, medium confidence) will likely affect human health and well-being, economic development, conservation, and agricultural productivity. Increased resilience will depend on collaboration and integrated planning, preparation, and responses across the region (high confidence).
' uncertainties: "There are still uncertainties as to how these projected changes in tropical Atlantic cyclone activity will affect the frequency distribution of extreme precipitation events. While an increase in days with more than 3 inches of rain per 24-hour period has been projected based on statistically downscaled CMIP3 models,{{< tbib '28' '56d77153-c8fc-4fcf-a7f0-fa0e843936f1' >}} more recent generations of GCMs do not show this increase in extreme rainfall events, and this adds uncertainty. Results from two dynamically downscaled climate models using the most recent generation of GCMs for the region do not show increases in the frequency of extreme events.{{< tbib '34' '744497bd-974c-497e-bf74-34ff514c0f83' >}}
At present, data pertaining to the costs and effects that are associated with extreme events and disasters are very limited and not readily accessible for government officials, disaster risk managers, or the general public. In the future, more accessible data could facilitate opportunities for more thorough analyses on the economic costs of extreme events for the U.S. Caribbean.
" uri: /report/nca4/chapter/us-caribbean/finding/key-message-20-5 url: ~ - chapter_identifier: us-caribbean confidence: 'There is high confidence that climate change will likely result in serious water supply shortages and in increased risks for agriculture production, human health, wildlife, and the socioeconomic development of Puerto Rico, the USVI, and the wider Caribbean region. The effects of climate change in the Caribbean region are likely to increase threats to life and infrastructure from sea level rise and extreme events; reduce the availability of fresh water, particularly during the dry season; negatively affect coral reef ecosystems; and cause health problems due to high temperatures and an increase in diseases.
' evidence: "Cross-regional and international cooperation is a mechanism that will likely reduce climate vulnerability and risks in the U.S. Caribbean, because it builds capacity and leverages resources in a region that has low adaptive capacity, due in part to the high costs of mitigation and adaptation relative to gross domestic product.{{< tbib '1' '63e4948c-5b46-4deb-a37b-9f363a1a8316' >}},{{
The majority of our Key Messages were developed over the course of two separate author meetings. The first occurred March 9–10, 2017, and the second on May 3, 2017. Both meetings were held in San Juan, Puerto Rico; however, people were also able to join remotely from Washington, DC, Raleigh, North Carolina, and the U.S. Virgin Islands (USVI). In addition, the author team held weekly conference calls and organized separate Key Message calls and meetings to review and draft information that was integral to our chapter. To develop the Key Messages, the team also deliberated with outside experts who are acknowledged as our technical contributors.
Shared knowledge, collaborative research and monitoring, and sustainable institutional adaptive capacity can help support and speed up disaster recovery, reduce loss of life, enhance food security, and improve economic opportunity in the U.S. Caribbean. Increased regional cooperation and stronger partnerships in the Caribbean can expand the region’s collective ability to achieve effective actions that build climate change resilience, reduce vulnerability to extreme events, and assist in recovery efforts (very likely, high confidence)
' uncertainties: 'There is high certainty that Caribbean island states are being affected by climate change, but the rate and degree of effects vary across countries due to the differences in environmental and socioeconomic conditions. Examples of regional cooperation efforts to share knowledge, conduct collaborative research, and develop joint projects have increased the adaptive capacity in the region; however, sustaining such efforts across the region remains a challenge. As efforts for regional coordination, cooperation, and information exchange evolve, evidence of the benefits of collaboration can be better assessed.
' uri: /report/nca4/chapter/us-caribbean/finding/key-message-20-6 url: ~ - chapter_identifier: midwest confidence: 'There is very high confidence that increases in warm-season absolute humidity and precipitation very likely have eroded soils, created favorable conditions for pests and pathogens, and degraded quality of stored grain. There is medium confidence that projected increases in moisture, coupled with rising mid-summer temperatures, likely will be detrimental to crop and livestock production and put future gains in commodity grain production at risk by mid-century. Projected changes in precipitation, coupled with rising extreme temperatures, provide medium confidence that by mid-century Midwest agricultural productivity likely will decline to levels of the 1980s without major technological advances.
' evidence: "Humidity is increasing. Feng et al. (2016){{< tbib '3' '28675f8a-8858-40ac-b53a-710b489bca07' >}} show plots of trends in surface and 850 hPa specific humidity of 0.4 and 0.2 g/kg/decade, respectively, from 1979–2014 for the April–May–June period across the Midwest. These represent increases of approximately 5% and 3% per decade, respectively. Automated Surface Observing Stations in Iowa{{< tbib '320' '9dc60b30-9bb1-46c8-aaea-9dba602c2d05' >}} having dew point records of this length and season show dew point temperature increases of about 1°F per decade. Brown and DeGaetano (2013){{< tbib '49' '83d23b83-2a04-4a6b-bdfa-caa8b54b1ccf' >}} show increasing dew points in all seasons throughout the Midwest. Observed changes in annual average maximum temperature for the Midwest over the 20th century (Vose et al. 2017,{{< tbib '54' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}} Table 6.1) have been less than 1°F. However, future projected changes in annual average temperature (Vose et al. 2017,{{< tbib '54' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}} Table 6.4), as well as in both warmest day of the year and warmest 5-day 1-in-10 year events (Vose et al. 2017,{{< tbib '54' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}} Table 6.5), are higher for the Midwest than in any other region of the United States.
Garbrecht et al. (2007){{< tbib '321' '232aa0b0-6c75-46f6-90df-85b58cfbb3b1' >}} state that precipitation changes are sufficient to require U.S. policy changes for agricultural lands. The Soil Erosion Site (http://soilerosion.net/water_erosion.html) describes the soil erosion process and provides links to soil erosion models.{{< tbib '322' '4baac62e-5892-4a0a-b435-e2cedc62f9a2' >}} Nearing et al. (2004){{< tbib '44' '43e7bfdb-30c7-407d-89ae-e94f7bff36a1' >}} report that global climate models project increases in erosivity (the ability or power of rain to cause soil loss) across the northern states of the United States over the 21st century.
Spoilage in stored grain is caused by mold growth and insect activity, which are related to the moisture content and temperature of the stored grain.{{< tbib '323' 'c65ba7e2-12f7-4a02-82c1-622c0aeb8711' >}} The ability of fungi to produce mycotoxins, including aflatoxin and fumonisins, is largely influenced by temperature, relative humidity, insect attack, and stress conditions of the plants.{{< tbib '57' '1ca7e70d-66b3-42e1-9a68-31b976d2622f' >}},{{
Germination of wheat declined in storage facilities where moisture level increased with time.{{< tbib '326' '5c614c37-2c94-413e-85d1-28d44b88d452' >}} Freshly harvested, high-moisture content grain must be dried to minimize (or prevent) excessive respiration and mold growth on grains.{{< tbib '327' '64513762-d666-447a-b19d-18bcd9cb0b80' >}} The storage life of grain is shortened significantly when stored at warm temperatures. One day of holding warm, wet corn before drying can decrease storage life by 50%.{{< tbib '45' '858d3935-f2b4-46d1-8c20-4fdf50922067' >}}
Feng et al. (2016){{< tbib '3' '28675f8a-8858-40ac-b53a-710b489bca07' >}} show humidity is rising in the Midwest in the warm season. Cook et al. (2008){{< tbib '4' 'e6bbc070-a723-4341-be6e-09bbd3248a20' >}} show that the factors leading to these humidity increases (warming Gulf of Mexico and strengthening of the Great Plains Low-Level Jet) will increase in a warming climate.
The ability of fungi to produce mycotoxins is largely influenced by temperature, relative humidity, insect attack, and stress conditions of the plants.{{< tbib '324' '2688cf64-d71f-4e21-84ad-f5cae499ed61' >}} More extreme rainfall events would favor formation of Deoxynivalenol, also known as vomitoxin.{{< tbib '57' '1ca7e70d-66b3-42e1-9a68-31b976d2622f' >}}
Hatfield et al. (2011,{{< tbib '50' 'a2704ef3-5be4-41ee-8dfa-4c82e416a292' >}} Table 1) give the relationships between temperature and vegetative function as well as reproductive capacity. This work was expanded and updated in Walthall et al. (2012).{{< tbib '328' '3baf471f-751f-4d68-9227-4197fdbb6e5d' >}}
Mader et al. (2010){{< tbib '74' '6a1bc03d-a204-4f8c-9779-73ee5c44e413' >}} report a comprehensive climate index for describing the effect of ambient temperature, relative humidity, radiation, and wind speed on environmental stress in animals. St-Pierre et al. (2003){{< tbib '329' 'ef0e1901-7533-4af4-b3b8-840a78ca4a49' >}} provide tables estimating economic losses in dairy due to reduced reproduction. The data show a strong gradient across the Midwest (with losses in Iowa, Illinois, and Indiana being three times the losses in Minnesota, Wisconsin, and Michigan under the current climate). Temperature and humidity increases projected for the Midwest will increase economic losses across the entire region. Lewis and Bunter (2010){{< tbib '330' '5eace42f-0819-4bec-a799-23c78ad4b486' >}} document heat stress effects of temperature on pig production and reproduction.
St-Pierre et al. (2003){{< tbib '329' 'ef0e1901-7533-4af4-b3b8-840a78ca4a49' >}} provide tables estimating economic losses in dairy, beef, swine, and poultry, resulting in declines from both meat/milk/egg production. The data show a strong gradient across the Midwest (with losses in Iowa, Illinois, and Indiana being twice the losses in Minnesota, Wisconsin, and Michigan under the current climate). Temperature and humidity increases projected for the Midwest will increase losses across the entire region. Babinszky et al. (2011){{< tbib '75' '3f7db557-5407-40cf-9078-d5be0f25ee0a' >}} identified temperature thresholds for meat/egg/milk production, beyond which performance declines. The adverse effects of heat stress include high mortality, decreased feed consumption, poor body weight gain and meat quality in broiler chickens, and poor laying rate, egg weight, and shell quality in laying hens.{{< tbib '76' '06f01e99-7afa-4be6-93ab-881cab8e56b8' >}}
Takle et al. (2013){{< tbib '65' '6e8fbacd-aff6-48ab-a950-5a8df2799046' >}} found that by mid-century, yields of corn and soybean are projected to fall well below projections based on extrapolation of trends since 1970 even under an optimistic economic scenario, with larger interannual variability in yield and total production. Liang et al. (2017){{< tbib '2' 'c5857041-2594-47cf-a6bc-3fab052fa903' >}} report that the ratio of measured agricultural output to measured inputs would drop by an average 3% to 4% per year under medium to high emissions scenarios and could fall to pre-1980 levels by 2050 even when accounting for present rates of innovation. Schauberger et al. (2017){{< tbib '66' '2967c8a9-063e-4118-92a4-71f266341e2f' >}} found that the impact of exposure to temperatures from 30°C to 36°C projected for the end of the century under RCP8.5 creates yield losses of 49% for maize and 40% for soybean.
According to Easterling et al. (2017),{{< tbib '193' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} evidence suggests that droughts have become less frequent in the Midwest as the region has become wetter. However, they note that “future higher temperatures will likely lead to greater frequencies and magnitudes of agricultural droughts throughout the continental United States as the resulting increases in evapotranspiration outpace projected precipitation increases.
" href: https://data.globalchange.gov/report/nca4/chapter/midwest/finding/key-message-21-1.yaml identifier: key-message-21-1 ordinal: 1 process: "The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.
Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.
Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).{{< tbib '315' 'fe83e7d3-3f29-4aef-81ae-28abd70dda2e' >}},{{
The Midwest is a major producer of a wide range of food and animal feed for national consumption and international trade. Increases in warm-season absolute humidity and precipitation have eroded soils, created favorable conditions for pests and pathogens, and degraded the quality of stored grain (very likely, very high confidence). Projected changes in precipitation, coupled with rising extreme temperatures before mid-century, will reduce Midwest agricultural productivity to levels of the 1980s without major technological advances (likely, medium confidence).
' uncertainties: "Global and regional climate models do not simulate well the dynamical structure of mesoscale convective systems in the Midwest, which are the critical “end processes” that create intense precipitation from increasing amounts of moisture evaporated over the Gulf of Mexico and transported by low-level jets (LLJs) into the Midwest. Secondly, the strengthening of future LLJs depends on strengthening of both the Bermuda surface high pressure and the lee surface low over the eastern Rocky Mountains. Confirming simulations of this in future climates are needed. Global and regional climate models do simulate future scenarios having increasing temperatures for the region with high confidence (a necessary ingredient for increased humidity). There is uncertainty of the temperature thresholds for crops because, as pointed out by Schauberger et al. (2017),{{< tbib '66' '2967c8a9-063e-4118-92a4-71f266341e2f' >}} some negative impacts of higher temperatures can be overcome through increased water availability. Agricultural yield models, productivity models, and integrated assessment models each provide different ways of looking at agricultural futures, and each of these three types of models has high levels of uncertainty. However, all point to agriculture futures that fail to maintain upward historical trends.
" uri: /report/nca4/chapter/midwest/finding/key-message-21-1 url: ~ - chapter_identifier: midwest confidence: 'There is high confidence that the interactions of warming temperatures, precipitation changes, and drought with insect pests, invasive plants, and tree pathogens will likely lead to increased tree mortality of some species, reducing productivity of some forests. There is very high confidence that these interactions will very likely result in the decline of some economically or culturally important tree species. Additionally, there is high confidence that suitable habitat conditions for tree species will change as temperatures increase and precipitation patterns change, making it likely that forest composition will be altered and forest ecosystems may shift to new forest types. Due to uncertainties on species migration rates and forest management responses to climate changes, there is medium confidence that by the end of the century, some forest ecosystems are as likely as not to convert to non-forest ecosystems.
' evidence: "Multiple ecosystem vulnerability assessments that have been conducted for major forested ecoregions within the Midwest{{< tbib '89' '8b4159ec-1edb-4fab-8af5-10a8cdec8fb5' >}},{{
Significant indirect impacts to forests are expected as warming increases the negative effects of invasive plants, insect pests, and tree pathogens of forests.{{< tbib '105' '98e8338c-3c49-49f7-9334-d4c28a901ad0' >}},{{
Direct and indirect impacts of climate change may lead to the decline of culturally{{< tbib '88' '7e39f05f-d63f-473a-87c3-93d733ea178b' >}},{{
Many examples of land managers implementing climate adaptation in forest management exist, suggesting significant willingness to address the impacts of a changing climate across diverse land ownerships in managed forests{{< tbib '134' '7242780c-93ee-4a39-9505-d0bd2f67c62b' >}} and urban forests.{{< tbib '133' '6352c444-c49b-4dac-b375-2b72b8532ebe' >}} Forest management strategies to adapt to a changing climate highlight the importance of increasing forest diversity and managing for tree species adapted to a range of climate conditions.{{< tbib '8' '28ab77d2-73c7-4554-82ef-c8bd5e095887' >}} The importance of Traditional Ecological Knowledge for informing approaches for climate adaptation on tribal lands and within ceded territory is recognized.{{< tbib '331' '44b1444b-29ab-4edd-b285-f8820660fc32' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/midwest/finding/key-message-21-2.yaml identifier: key-message-21-2 ordinal: 2 process: "The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.
Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.
Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).{{< tbib '315' 'fe83e7d3-3f29-4aef-81ae-28abd70dda2e' >}},{{
Midwest forests provide numerous economic and ecological benefits, yet threats from a changing climate are interacting with existing stressors such as invasive species and pests to increase tree mortality and reduce forest productivity (likely, high confidence). Without adaptive actions, these interactions will result in the loss of economically and culturally important tree species such as paper birch and black ash (very likely, very high confidence) and are expected to lead to the conversion of some forests to other forest types (likely, high confidence) or even to non-forested ecosystems by the end of the century (as likely as not, medium confidence). Land managers are beginning to manage risk in forests by increasing diversity and selecting for tree species adapted to a range of projected conditions.
' uncertainties: 'There is significant uncertainty surrounding the ability of tree species migration rates to keep pace with changes in climate (based on temperature and precipitation) due to existing forest fragmentation and loss of habitat. Uncertainty in forest management responses, including active and widespread adaptation efforts that alter forest composition, add to the uncertainty of tree species movements. This leads to considerable uncertainty in the extent to which shifts in tree species ranges may lead to altered forest composition or loss of forest ecosystems in the future.
Due to the complex interactions among species, there is uncertainty in the extent that longer growing seasons, warming temperatures, and increased CO2 concentrations will benefit tree species, due to both limitations in available water and nutrients, as well as limited benefits for trees relative to the positive influences of these changes on stressors (invasives, insect pests, pathogens).
' uri: /report/nca4/chapter/midwest/finding/key-message-21-2 url: ~ - chapter_identifier: midwest confidence: 'In the Midwest, we already have seen very high levels of habitat loss and conversion, especially in grasslands, wetlands, and freshwater systems. This habitat degradation, in addition to the pervasive impacts of invasive species, pollution, water extraction, and lack of connectivity, all suggest that the adaptive capacity of species and systems is compromised relative to systems that are more intact and under less stress. Over time, this pervasive habitat loss and degradation has contributed to population declines, especially for wetland, prairie, and stream species. A reliance on cold surface-water systems, which often have compromised connectivity (due to dams, road-stream crossings with structures that impede stream flow, and other barriers) suggests that freshwater species, especially less mobile species like mussels, which are already rare, are at particular risk of declines and extinction. Due to the variety of life histories and climate sensitivities of species within the region, it is very challenging to specify what mechanisms will be most important in terms of driving change. However, knowing that drivers like invasive species, habitat loss, pollution, and hydrologic modifications promote species declines, it is very likely that the effects of climate change will interact, and we have very high confidence that these interactions will tend to increase, rather than decrease, stresses on species that are associated with these threats. While there is strong evidence that investments in restoring habitat can benefit species, we currently do not have strong observational evidence of the use of these new habitats, or benefits of restored wetlands, in response to isolated climate drivers. Thus, the confidence level for this statement is lower than for the first half of the message.
' evidence: "Changes in climate will very likely stress many species and ecological systems in the Midwest. As a result of increases in climate stressors, which typically interact with multiple other stressors, especially in the southern half of the Midwest region, both the ecological systems and the ecological services (water purification, pollination of crops and wild species, recreational opportunities, etc.) they provide to people are at risk. We draw from a wide range of national and global scale assessments of risks to biodiversity (e.g., Maclean and Wilson 2011, Pearson et al. 2014, and the review by Staudinger et al. 2013 that covered literature included in the Third National Climate Assessment{{< tbib '20' 'a0f111d8-ec32-486c-83a9-c9f359854550' >}},{{< tbib '18' 'b0d94572-aa34-47e0-bddf-0a8e7e0c60bb' >}},{{< tbib '22' '506759aa-765f-4007-a678-17d69d139e39' >}}), which all agree that on the whole, we are highly likely to see increases in species declines and extinctions as a result of climate change. It is very challenging to say specifically what combination of factors will drive these responses, but the weight of evidence suggests very high confidence in the overall trends. The link to interactions with other stressors is also very strong and is described in Brook et al. (2008){{< tbib '157' '5cee6e59-0713-4a56-abae-6f60119df8e5' >}} and Cahill et al. (2013),{{< tbib '17' '4da26e14-8c1a-4f66-8212-a98880263e91' >}} among others. Terrestrial ecosystem connectivity, thought to be important for the adaptive capacity of many species, is very low in the southern half of the Midwest region.{{< tbib '158' '3c96d70c-9523-49e8-b7aa-0a86be8992a0' >}},{{
The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.
Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.
Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).{{< tbib '315' 'fe83e7d3-3f29-4aef-81ae-28abd70dda2e' >}},{{
The ecosystems of the Midwest support a diverse array of native species and provide people with essential services such as water purification, flood control, resource provision, crop pollination, and recreational opportunities. Species and ecosystems, including the important freshwater resources of the Great Lakes, are typically most at risk when climate stressors, like temperature increases, interact with land-use change, habitat loss, pollution, nutrient inputs, and nonnative invasive species (very likely, very high confidence). Restoration of natural systems, increases in the use of green infrastructure, and targeted conservation efforts, especially of wetland systems, can help protect people and nature from climate change impacts (likely, high confidence).
' uncertainties: "There is significant uncertainty surrounding the ability of species and ecosystems to persist and thrive under climate change, and we expect to see many different types of responses (population increases, declines, local and regional extinctions).{{< tbib '17' '4da26e14-8c1a-4f66-8212-a98880263e91' >}} In some cases, climate change does have the potential to benefit species; for example, fish in the coldest regions of the Great Lakes (i.e., Lake Superior) are likely to show increases in productivity, at least in the short run.{{< tbib '332' '8a6a8c87-01dc-4370-a982-afe4207f1962' >}} However, as a whole, given the environmental context upon which climate change is operating, and the presence of many cold-adapted species that are close to the southern edge of their distributional range, we expect more declines than increases.
The last section of the Key Message focuses on land protection and restoration—conservation strategies intended to reduce the impacts of land-use change. Many modeling studies have called out loss of habitat in the Midwest as a key barrier to both local survival and species movement in response to climate change (Schloss et al. 2012 and Carroll et al. 2015 are two of the most recent{{< tbib '158' '3c96d70c-9523-49e8-b7aa-0a86be8992a0' >}},{{< tbib '158' '3c96d70c-9523-49e8-b7aa-0a86be8992a0' >}}). Restoring habitat can restore connectivity and protect key ecological functions like pollination services and water purification. Restoring wetlands also can help protect ecosystems and people from flooding, which is the rationale for the last line in the Key Message.
" uri: /report/nca4/chapter/midwest/finding/key-message-21-3 url: ~ - chapter_identifier: midwest confidence: 'Based on the evidence, there is very high confidence that climate change is very likely to impact midwesterners’ health.
' evidence: "There is strong evidence that increasing temperatures and precipitation in the Midwest will occur by the middle and end of the 21st century.{{< tbib '27' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} The impacts of these changes on human health are broadly captured in the 2016 U.S. Global Change Research Program’s Climate and Health Assessment.{{< tbib '26' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} Air quality, including particulate matter and ground-level ozone, is positively associated with increased temperatures and has been well-documented to show deleterious impacts on morbidity and mortality.{{< tbib '231' '5ec155e5-8b77-438f-afa9-fbcac4d27690' >}} Likewise, increased temperatures have been shown in communities in the Midwest, as well as across the United States, to have substantial impacts on health and well-being.{{< tbib '232' 'dac369a3-921e-426f-b4a2-5798dfb9c515' >}},{{
Access to basic preventive care measures quantifiably reduces disease burden for climate-sensitive exposures.{{< tbib '238' '327a1728-7992-448b-9e5b-267328259994' >}},{{
The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.
Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.
Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).{{< tbib '315' 'fe83e7d3-3f29-4aef-81ae-28abd70dda2e' >}},{{
Climate change is expected to worsen existing conditions and introduce new health threats by increasing the frequency and intensity of poor air quality days, extreme high temperature events, and heavy rainfalls; extending pollen seasons; and modifying the distribution of disease-carrying pests and insects (very likely, very high confidence). By mid-century, the region is projected to experience substantial, yet avoidable, loss of life, worsened health conditions, and economic impacts estimated in the billions of dollars as a result of these changes (likely, high confidence). Improved basic health services and increased public health measures—including surveillance and monitoring—can prevent or reduce these impacts (likely, high confidence).
' uncertainties: 'While the modeling performed by the EPA was completed using the best available information, there is uncertainty around the extent to which biophysical adaptations will protect midwestern populations from heat-, air pollution-, aeroallergen-, and vector-related illness and death. Likewise, while there is a general consensus regarding habitat suitability for disease-carrying vectors in the eastern and western United States, the degree to which the disease burden may increase or decrease is largely uncertain.
' uri: /report/nca4/chapter/midwest/finding/key-message-21-4 url: ~ - chapter_identifier: midwest confidence: 'There is medium confidence that climate change is contributing to increased flood risk in the Midwest; there is medium confidence that green infrastructure is reducing flood risk. There is much uncertainty associated with specific numerical projections. This leads to medium confidence that costs will exceed $500 million. However, the EPA projections are sufficient to provide high confidence that increasing the capacity of existing storm water systems in order to maintain current levels of service would require significant expenditures on the part of urban sewer districts.
' evidence: "The patterns of increased annual precipitation, and the size and frequency of heavy precipitation events in the Midwest, are shown in numerous studies and highlighted in Melillo et al. (2014){{< tbib '27' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} and Easterling et al. (2017).{{< tbib '193' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} Increases in annual precipitation of 5% to 15% are reported across the Midwest region.{{< tbib '193' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} In addition, both the frequency and the intensity of heavy precipitation events in the Midwest have increased since 1901.{{< tbib '193' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}
For the early 21st century (2016–2045), both lower and higher scenarios (RCP4.5 and RCP8.5) indicate that average annual precipitation could increase by 1% to 5% across the Midwest, suggesting that the observed increases are likely to continue. By mid-century (2036–2065), both scenarios (RCP4.5 and RCP8.5) indicate precipitation increases of 1% to 5% in Missouri and Iowa and 5% to 10% increases in states to the north and east. By late century (2070–2089), precipitation is expected to increase by 5% to 15% over present day, with slightly larger increases in the higher scenario (RCP8.5). Model simulations suggest that most of these increases will occur in winter and spring over the 21st century. Similar to annual precipitation, the amounts from the annual maximum one-day precipitation events (a measure of heavy precipitation events) are projected to increase over time in the Midwest. The size of the events could increase by 5% to 15% by late century.{{< tbib '193' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}}
Gray literature documents that heavy rains in the Midwest are overwhelming storm water management systems, leading to property damage. Kenward et al. (2016){{< tbib '256' 'e9ccb2ed-ba08-43aa-8895-a21908f6d691' >}} provide examples of rain-related sewage overflows in the Midwest. These include an overflow of 681 million gallons during heavy rains in April 2015 in Milwaukee and an overflow of over 100 million gallons from December 26–28, 2015, in St. Louis. Winters et al. (2015){{< tbib '37' '0fe1cea1-aae3-4a35-b78f-61dcb5d6df49' >}} document that failure of storm water management systems in heavy rain leads to property damage, including basement backups.
The disruption of transportation networks by heavy precipitation in the Midwest has been documented by collecting contemporary news reports and by compiling state government reports. Posey (2016){{< tbib '338' 'd9754ccb-d173-4624-8e6a-1efb9a37b556' >}} relates that four storms between April 2013 and April 2014 forced evacuations or damaged cars in St. Louis, Missouri. In the same period, there were 18 flood-related closures on Missouri roads, a figure that excludes closures on small local roads. Flooding in May 2017 led to the closure of more than 400 roads across Missouri, a figure that again excludes local roads. Closed roadways included multiple stretches of Interstate 44, as well as sections of I-55, affecting interstate traffic between St. Louis and Memphis.{{< tbib '339' 'bb613b8d-1aae-425c-b4b5-5274d1460d42' >}} News reports document that the same stretch of I-44 was shut down during the floods of December 2015–January 2016.{{< tbib '340' '7529ed72-74b6-4f77-bf19-8aeeb1ab5ae0' >}}
Flood-related disruptions to Midwest barge and rail traffic in 2013 were documented by several articles in Journal of Commerce, a shipping trade magazine.{{< tbib '265' 'cad15039-4add-470a-bac2-adeb08e201c4' >}},{{
Although there is ample documentation of transportation systems in the Midwest being disrupted by floods in recent years, there is a lack of long-term time series data on disruptions with which to determine whether these incidents are becoming more frequent. Development of long-term data on transportation disruptions in the Midwest is a research need. It is clear that flood frequency and severity on major rivers in the Midwest have increased in recent decades, although additional research is needed on the relative contributions of climate change and land-use change to increases in flood risk.{{< tbib '344' 'aa980625-eab7-45f5-9bcb-d8dbbd36e6c7' >}},{{
The EPA estimated economic costs related to infrastructure and transportation in the Midwest, including costs associated with bridge scour and pavement degradation.{{< tbib '28' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} The use of green infrastructure to reduce impacts associated with heavy precipitation is also documented in gray literature, including municipal planning documents. Using planted areas to absorb rainfall and reduce runoff has become a common approach to storm water management.{{< tbib '223' 'b71cbf27-2a1d-477e-9d0a-4d49b427ed47' >}},{{
The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.
Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.
Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).{{< tbib '315' 'fe83e7d3-3f29-4aef-81ae-28abd70dda2e' >}},{{
Storm water management systems, transportation networks, and other critical infrastructure are already experiencing impacts from changing precipitation patterns and elevated flood risks (medium confidence). Green infrastructure is reducing some of the negative impacts by using plants and open space to absorb storm water (medium confidence). The annual cost of adapting urban storm water systems to more frequent and severe storms is projected to exceed $500 million for the Midwest by the end of the century (medium confidence).
' uncertainties: "Although there is very high confidence that flood risk is increasing in the Midwest, there remains uncertainty about the relative contributions of climate change and land-use change. There is, however, sufficient evidence that changing precipitation patterns are leading to changes in hydrology in the Midwest,{{< tbib '351' 'c9d0a7e9-2bba-48cb-bd53-9e8c4209976d' >}},{{
While it is clear that flood frequency and severity on major rivers in the Midwest have increased in recent decades, it must be emphasized that the change in precipitation levels is not the only factor contributing to the increase in flood risk. Land-use change, particularly the destruction of floodplains by levee systems, has also been documented as a key contributor to increasing flood risk in the Midwest.{{< tbib '344' 'aa980625-eab7-45f5-9bcb-d8dbbd36e6c7' >}},{{
There is high confidence that communities in the Midwest will as likely as not be increasingly vulnerable to climate change impacts such as flooding, urban heat islands, and drought. Similarly, there is medium confidence that tribal nations in the Midwest are likely to be especially vulnerable because of their reliance on threatened natural resources for their cultural, subsistence, and economic needs. Due to limited documentation in the literature, there is medium confidence that integrating adaptation into planning processes will offer an opportunity to manage climate risk better. Finally, there is high confidence that developing knowledge for decision-making in cooperation with vulnerable communities and tribal nations will help to decrease sensitivity and build adaptive capacity.
' evidence: "Limited evidence in the scientific literature indicates that at-risk communities in the Midwest will be increasingly vulnerable to the impacts of climate change, including increased flooding resulting from increased variation in precipitation patterns and changing lake levels,{{< tbib '285' 'c9ef5059-729c-4701-ad9a-da15255bd5ca' >}} urban heat islands,{{< tbib '287' '34db2d46-ef90-43a4-99ab-40dae17afcce' >}} and an intensification of heat and drought (see also the impacts and associated references in the previous sections).{{< tbib '286' 'b228ac0d-7bf9-4391-99e7-5c598b9ce55e' >}}
Several recent survey reports{{< tbib '28' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
Gray literature,{{< tbib '293' '3c3cc09b-c2d7-4c52-bf8f-c064efa78e93' >}} survey reports,{{< tbib '32' 'b74c5cc9-2e40-4ad9-92aa-f2b02c7a4be7' >}} and scientific literature{{< tbib '292' '660ac034-1441-4d28-98e2-61c8c252348a' >}} point to a few initiatives to integrate adaptation into municipal planning processes and utilize participatory methodologies to evaluate and manage climate risk.
A growing body of research indicates that interaction between producers of climate information, intermediaries, and end users plays a critical role in increasing climate knowledge integration and use for adaptation in the Midwest.{{< tbib '224' '7b490de7-7bcd-4e31-b512-9deaa3a5eba7' >}},{{
The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.
Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.
Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).{{< tbib '315' 'fe83e7d3-3f29-4aef-81ae-28abd70dda2e' >}},{{
At-risk communities in the Midwest are becoming more vulnerable to climate change impacts such as flooding, drought, and increases in urban heat islands (as likely as not, high confidence). Tribal nations are especially vulnerable because of their reliance on threatened natural resources for their cultural, subsistence, and economic needs (likely, medium confidence). Integrating climate adaptation into planning processes offers an opportunity to better manage climate risks now (medium confidence). Developing knowledge for decision-making in cooperation with vulnerable communities and tribal nations will help to build adaptive capacity and increase resilience (high confidence).
' uncertainties: 'Limited research specific to the Midwest region contributes to uncertainty around the specific vulnerabilities of at-risk communities, including urban and rural communities and tribal nations. Though climate change planning and action in both Midwest cities and rural areas are underway, documentation remains low, few examples exist in the public literature of the failure or success of efforts to mainstream climate action into municipal governance, and attempts to assess vulnerabilities, especially in poor urban communities, frequently encounter climate justice barriers. Likewise, the number, scope, and nature of tribal adaptation plans remain undocumented, as does the degree of implementation of these plans and the manner in which Traditional Ecological Knowledge is incorporated.
' uri: /report/nca4/chapter/midwest/finding/key-message-21-6 url: ~ - chapter_identifier: northern-great-plains confidence: 'There is high confidence that temperatures will rise in the region, which will likely produce less snowfall and smaller mountain snowpacks. There is very high confidence in the downstream consequences of these changes.
' evidence: "Multiple lines of research have shown that as a result of its high aridity, changes in water availability in the Northern Great Plains region are highly sensitive to small changes in climate.{{< tbib '35' '8c567c0c-cc42-4372-94ea-7abf677704c6' >}},{{
Natural reservoirs, groundwater, and snowpack are at risk to varying degrees. Reservoir vulnerability was recently analyzed to assess sustainable pumping rates,{{< tbib '42' 'bbb70780-07ef-4083-a3ff-8dc8d33b1e62' >}} while snow and especially glaciers appear to be in steady decline in recent decades,{{< tbib '38' 'bb0be3c7-6d67-4281-9ff4-db244460b65a' >}} attributed to global climate warming{{< tbib '39' '760d96a6-ba98-4e20-8897-2989d8f0ae6f' >}} that is projected to continue.{{< tbib '145' '29dec54f-92a8-4543-93f1-941da4f4d750' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/northern-great-plains/finding/key-message-22-1.yaml identifier: key-message-22-1 ordinal: 1 process: 'The chapter lead (CL) and coordinating lead author (CLA) developed a list of potential contributing authors by soliciting suggestions from the past National Climate Assessment (NCA) author team, colleagues and collaborators throughout the region, and contributors to other regional reports. Our initial list of potential authors also included CL nominees submitted to the U.S. Global Change Research Program (USGCRP). The CL and CLA discussed the Northern Great Plains, which was part of the larger Great Plains region for the Third National Climate Assessment (NCA3), with each of these nominees and, as part of that discussion, solicited suggestions for other nominees. This long list of potential contributing authors was pared down by omitting individuals who could not contribute in a timely fashion, and the list was finalized after reconciliation against key themes within the region identified by past NCA authors, the CL and CLA, and contributing author nominees. The team of contributing authors was selected to represent the region geographically and thematically, but participants from some states who had agreed to contribute were eventually unable to do so. Others were unable to contribute from the start. The author team is mostly composed of authors who did not contribute to NCA3.
The CL and CLA, in consultation with past NCA authors and contributing author nominees, identified an initial list of focal areas of regional importance. The author team then solicited input from colleagues and regional experts (identified based on their deep ties to scientific and practitioner communities across the region) on their thoughts on focal areas. This list informed the agenda of a region-wide meeting held on February 22, 2017, with core locations in Fort Collins, Colorado, and Rapid City, South Dakota. The main purpose of this meeting was to seek feedback on the proposed list of focal areas. With this feedback, the author team was able to refine our focal areas to the five themes comprising the Key Messages of the Northern Great Plains regional chapter. Of these, recreation/tourism is a focus area that is new from NCA3.
' report_identifier: nca4 statement: 'Water is the lifeblood of the Northern Great Plains, and effective water management is critical to the region’s people, crops and livestock, ecosystems, and energy industry. Even small changes in annual precipitation can have large effects downstream (very high confidence); when coupled with the variability from extreme events, these changes make managing these resources a challenge (very high confidence). Future changes in precipitation patterns, warmer temperatures, and the potential for more extreme rainfall events are very likely to exacerbate these challenges (very likely, high confidence).
' uncertainties: "While there is high confidence in future increases in temperature, uncertainties exist as to the changes in precipitation and runoff. Perhaps most important are the uncertainties in the degree of precipitation variability from year to year and within season (based on information dating to the 1950s).{{< tbib '35' '8c567c0c-cc42-4372-94ea-7abf677704c6' >}},{{
Uncertainties exist in agricultural demands for water, reservoir operation protocols, and changes in extreme events.
" uri: /report/nca4/chapter/northern-great-plains/finding/key-message-22-1 url: ~ - chapter_identifier: northern-great-plains confidence: "There is very high confidence that longer growing seasons have already benefited agriculture in parts of the Northern Great Plains. There is very high confidence that increases in temperatures and atmospheric CO2 will likely increase production potential for the agricultural sector in the short term (the next 10–20 years) and that current adaptations already being implemented by a subset of producers in this region provide opportunities for assessment, further development, and adoption by the larger population of agricultural managers. There is very high confidence that rising temperatures and changes in extreme weather events are very likely to have negative impacts on parts of the region. Over the longer-term (through the end of the 21st century), predicted climate changes may require transformative changes in agricultural management, including regional shifts of agricultural practices and enterprises (very likely, high confidence).{{< tbib '61' '18bc8646-9568-4169-a526-daed1216a4f0' >}},{{
Several lines of research have shown that agricultural productivity is likely to increase in rangelands across the region with increasing atmospheric carbon dioxide (CO2) and warming,{{< tbib '3' '26b61192-351a-494d-84f8-411c3e4ccd48' >}},{{
Numerous lines of research have addressed adaptation strategies for various parts of the agricultural sector{{< tbib '9' 'b1cbd298-7ce4-4106-a802-f8de95517c97' >}},{{
The chapter lead (CL) and coordinating lead author (CLA) developed a list of potential contributing authors by soliciting suggestions from the past National Climate Assessment (NCA) author team, colleagues and collaborators throughout the region, and contributors to other regional reports. Our initial list of potential authors also included CL nominees submitted to the U.S. Global Change Research Program (USGCRP). The CL and CLA discussed the Northern Great Plains, which was part of the larger Great Plains region for the Third National Climate Assessment (NCA3), with each of these nominees and, as part of that discussion, solicited suggestions for other nominees. This long list of potential contributing authors was pared down by omitting individuals who could not contribute in a timely fashion, and the list was finalized after reconciliation against key themes within the region identified by past NCA authors, the CL and CLA, and contributing author nominees. The team of contributing authors was selected to represent the region geographically and thematically, but participants from some states who had agreed to contribute were eventually unable to do so. Others were unable to contribute from the start. The author team is mostly composed of authors who did not contribute to NCA3.
The CL and CLA, in consultation with past NCA authors and contributing author nominees, identified an initial list of focal areas of regional importance. The author team then solicited input from colleagues and regional experts (identified based on their deep ties to scientific and practitioner communities across the region) on their thoughts on focal areas. This list informed the agenda of a region-wide meeting held on February 22, 2017, with core locations in Fort Collins, Colorado, and Rapid City, South Dakota. The main purpose of this meeting was to seek feedback on the proposed list of focal areas. With this feedback, the author team was able to refine our focal areas to the five themes comprising the Key Messages of the Northern Great Plains regional chapter. Of these, recreation/tourism is a focus area that is new from NCA3.
' report_identifier: nca4 statement: 'Agriculture is an integral component of the economy, the history, and the culture of the Northern Great Plains. Recently, agriculture has benefited from longer growing seasons and other recent climatic changes (very high confidence). Some additional production and conservation benefits are expected in the next two to three decades as land managers employ innovative adaptation strategies (very likely, high confidence), but rising temperatures and changes in extreme weather events are very likely to have negative impacts on parts of the region (very likely, very high confidence). Adaptation to extremes and to longer-term, persistent climate changes will likely require transformative changes in agricultural management, including regional shifts of agricultural practices and enterprises (very likely, high confidence).
' uncertainties: "While there is high confidence in future increases in temperature, uncertainties exist as to the changes in extreme events, including the spatiotemporal aspects of high-intensity rainfall events, snowstorms, and hailstorms. Perhaps most important are the uncertainties in the degree of precipitation variability from year to year{{< tbib '35' '8c567c0c-cc42-4372-94ea-7abf677704c6' >}} that influence decision-making calendars for agricultural producers.
" uri: /report/nca4/chapter/northern-great-plains/finding/key-message-22-2 url: ~ - chapter_identifier: northern-great-plains confidence: 'We know with very high confidence that ecosystems across the Northern Great Plains provide recreational opportunities and other valuable goods and services. We know with very high confidence that climate change is very likely affecting abiotic factors that influence these ecosystems, such as snowfall, spring snowmelt, runoff, and stream temperatures. There is high confidence that these abiotic factors are likely to affect high-elevation ecosystems and riparian areas in the Northern Great Plains. Greater confidence could be gained by conducting studies specifically within the Northern Great Plains, as opposed to drawing inferences from studies conducted in other regions of the world with similar characteristics. The consequences of ecosystem changes for local economies in the region that depend on winter-based or river-based recreational activities are currently being debated in the scientific literature, due to uncertainty about potential individual behavioral responses to changes in the recreational environment. Based on a limited number of case studies, effects of climate change on outdoor recreation-based economies are as likely as not to be negative, but this is only known with medium confidence. We know with very high confidence, however, that some natural ecosystems that local economies depend upon—in this specific case, wetlands in the Northern Great Plains—are likely to be negatively affected by climate-induced changes in agricultural land use. In turn, we know with high confidence that wetland declines will very likely harm the diverse species and recreational amenities they support. Uncertainty about future policies that could influence agricultural land-use decisions and wetland conservation outcomes precludes a higher confidence level or higher likelihood.
' evidence: "State-level surveys, conducted roughly every five years, have consistently documented that the public spends millions of days each year (over $30 million in 2011) participating in nature-based recreation activities in the Northern Great Plains (e.g., U.S. Department of the Interior and U.S. Department of Commerce 2008, 2013a, 2013b, 2014a, 2014b{{< tbib '65' 'ff8fa307-6c14-4764-83f9-9529b7bd688c' >}},{{
The chapter lead (CL) and coordinating lead author (CLA) developed a list of potential contributing authors by soliciting suggestions from the past National Climate Assessment (NCA) author team, colleagues and collaborators throughout the region, and contributors to other regional reports. Our initial list of potential authors also included CL nominees submitted to the U.S. Global Change Research Program (USGCRP). The CL and CLA discussed the Northern Great Plains, which was part of the larger Great Plains region for the Third National Climate Assessment (NCA3), with each of these nominees and, as part of that discussion, solicited suggestions for other nominees. This long list of potential contributing authors was pared down by omitting individuals who could not contribute in a timely fashion, and the list was finalized after reconciliation against key themes within the region identified by past NCA authors, the CL and CLA, and contributing author nominees. The team of contributing authors was selected to represent the region geographically and thematically, but participants from some states who had agreed to contribute were eventually unable to do so. Others were unable to contribute from the start. The author team is mostly composed of authors who did not contribute to NCA3.
The CL and CLA, in consultation with past NCA authors and contributing author nominees, identified an initial list of focal areas of regional importance. The author team then solicited input from colleagues and regional experts (identified based on their deep ties to scientific and practitioner communities across the region) on their thoughts on focal areas. This list informed the agenda of a region-wide meeting held on February 22, 2017, with core locations in Fort Collins, Colorado, and Rapid City, South Dakota. The main purpose of this meeting was to seek feedback on the proposed list of focal areas. With this feedback, the author team was able to refine our focal areas to the five themes comprising the Key Messages of the Northern Great Plains regional chapter. Of these, recreation/tourism is a focus area that is new from NCA3.
' report_identifier: nca4 statement: 'Ecosystems across the Northern Great Plains provide recreational opportunities and other valuable goods and services that are at risk in a changing climate (very high confidence). Rising temperatures have already resulted in shorter snow seasons, lower summer streamflows, and higher stream temperatures and have negatively affected high-elevation ecosystems and riparian areas, with important consequences for local economies that depend on winter or river-based recreational activities (high confidence). Climate-induced land-use changes in agriculture can have cascading effects on closely entwined natural ecosystems, such as wetlands, and the diverse species and recreational amenities they support (very high confidence, likely). Federal, tribal, state, and private organizations are undertaking preparedness and adaptation activities, such as scenario planning, transboundary collaboration, and development of market-based tools.
' uncertainties: 'Climate change is expected to disrupt local economies that depend on winter-based or river-based recreational activities. However, the magnitudes of these effects are uncertain. This is due largely to uncertainties about the preferences of recreationalists and the extent to which they will adapt by shifting the timing and location of their activities or by substituting towards a different set of recreational activities. For example, although climate change will make it more difficult to supply high-quality downhill skiing opportunities, this effect will be stronger in lower-elevation areas. Therefore, some skiers might adapt by simply traveling to higher-elevation downhill ski areas. Others might compensate for the shorter ski season at their favorite lower-elevation mountain by shifting some of their recreational time to an alternative outdoor activity, such as winter mountain biking. Given the potential diversity of individual preferences for adapting outdoor recreation activities to climate change, it is challenging to project with certainty the future potential impacts to recreation-dependent economies, but the impact will be larger and more immediate for some industries and companies (e.g., low-altitude ski resorts).
Another source of uncertainty is the reliance, in some cases, on scientific studies from other geographic locations to infer what the impacts of climate change might be for ecosystems, species, or recreationalists within the Northern Great Plains. For example, the effects of increased stream temperature on the susceptibility of coldwater fish species to diseases in the region are based largely on studies conducted in European coldwater fisheries.
Regarding wetlands in the Prairie Pothole Region, uncertainty about their abundance in the future arises from uncertainty about future government policies that would either exacerbate or mitigate climate-induced losses. For example, future versions of the Farm Bill may contain language that directly encourages wetland preservation (e.g., through conservation-compliance requirements) or unintentionally leads to wetland degradation (e.g., through higher subsidies for row crop insurance).
' uri: /report/nca4/chapter/northern-great-plains/finding/key-message-22-3 url: ~ - chapter_identifier: northern-great-plains confidence: 'There is high confidence that climate change and extreme weather events will likely put energy supply and infrastructure of various types at risk. There is high confidence that the energy sector is a very likely a significant source of greenhouse gases contributing to climate change. There is very high confidence that volatile organic compounds contribute to climate change and ground-level ozone pollution, and it is likely that this will worsen in the future in some areas.
' evidence: "Fossil fuel and renewable energy production/distribution infrastructure is expanding within the Northern Great Plains, including oil and natural gas pipelines, natural gas compressor stations and storage tanks, natural gas processing plants, natural gas-fired power plants, high-voltage power lines and substations, wind farms, and even a new oil refinery and a new biorefinery in recent years (both began operations in 2015).
A number of oil and natural gas pipelines are being constructed or have been completed in recent years. In particular, the Dakota Access Pipeline began commercial service June 1, 2017, transporting crude oil from the Bakken/Three Forks production areas in North Dakota, through South Dakota and Iowa, to Pakota, Illinois. While pipelines are vulnerable to damage or disruption from heavy precipitation events and associated flooding and erosion,{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}} their increased use could eliminate hundreds of rail cars and trucks needed to transport crude every day. This reduces the exposure of these modes of transportation to rising temperatures, heat waves, and floods.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}} Other oil and gas production and distribution infrastructure is similarly vulnerable to heavy precipitation events and flooding.
The region relies on rail lines to transport coal, and these lines are vulnerable to rising temperatures, heat waves, and floods.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}} There is ample evidence of rail line vulnerability to extreme weather.{{< tbib '151' '96b39da1-771b-4889-8535-6b3ba61b7042' >}}
Damage to thermoelectric power plants and electric power transmission lines from extreme weather such as heat waves and wildfires has been documented, and the risk is expected to increase.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}},{{
The U.S. Department of Energy (DOE) Energy Risk Profiles (1996–2014) highlight the risks to energy infrastructure in the United States from natural hazards. For example, in North Dakota, thunderstorms and lightning had the highest frequency of occurrence and property loss during this timeframe. DOE also has a series of comprehensive documents on U.S. energy sector vulnerabilities to climate change{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}},{{
There is substantial evidence that the energy sector is a significant source of greenhouse gases that contribute to climate change, in particular from power plants, oil and gas systems, and refineries.{{< tbib '117' '81430bfc-5d67-4109-982a-4cfd344f057c' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/northern-great-plains/finding/key-message-22-4.yaml identifier: key-message-22-4 ordinal: 4 process: 'The chapter lead (CL) and coordinating lead author (CLA) developed a list of potential contributing authors by soliciting suggestions from the past National Climate Assessment (NCA) author team, colleagues and collaborators throughout the region, and contributors to other regional reports. Our initial list of potential authors also included CL nominees submitted to the U.S. Global Change Research Program (USGCRP). The CL and CLA discussed the Northern Great Plains, which was part of the larger Great Plains region for the Third National Climate Assessment (NCA3), with each of these nominees and, as part of that discussion, solicited suggestions for other nominees. This long list of potential contributing authors was pared down by omitting individuals who could not contribute in a timely fashion, and the list was finalized after reconciliation against key themes within the region identified by past NCA authors, the CL and CLA, and contributing author nominees. The team of contributing authors was selected to represent the region geographically and thematically, but participants from some states who had agreed to contribute were eventually unable to do so. Others were unable to contribute from the start. The author team is mostly composed of authors who did not contribute to NCA3.
The CL and CLA, in consultation with past NCA authors and contributing author nominees, identified an initial list of focal areas of regional importance. The author team then solicited input from colleagues and regional experts (identified based on their deep ties to scientific and practitioner communities across the region) on their thoughts on focal areas. This list informed the agenda of a region-wide meeting held on February 22, 2017, with core locations in Fort Collins, Colorado, and Rapid City, South Dakota. The main purpose of this meeting was to seek feedback on the proposed list of focal areas. With this feedback, the author team was able to refine our focal areas to the five themes comprising the Key Messages of the Northern Great Plains regional chapter. Of these, recreation/tourism is a focus area that is new from NCA3.
' report_identifier: nca4 statement: 'Fossil fuel and renewable energy production and distribution infrastructure is expanding within the Northern Great Plains (very high confidence). Climate change and extreme weather events put this infrastructure at risk, as well as the supply of energy it contributes to support individuals, communities, and the U.S. economy as a whole (likely, high confidence). The energy sector is also a significant source of greenhouse gases (very likely, very high confidence) and volatile organic compounds that contribute to climate change and ground-level ozone pollution (likely in some areas, very high confidence).
' uncertainties: "Cold waves are projected to be less intense in the future, reducing the risk of disruptions from cold to energy infrastructure.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}}
There is not yet substantial agreement among sources as to how a changing climate will ultimately affect wind resources in the United States in general and in the Northern Great Plains in particular.{{< tbib '153' 'b66b1462-75b3-4a9b-ae8d-de2e190cf84b' >}}
Projected increases in precipitation in the Northern Great Plains are likely to benefit hydropower production, but this will vary by location. For example, it is known that in the Columbia River Basin, decreasing summer streamflows will reduce downstream hydropower production, and increasing winter and early spring streamflows will increase production.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}} In the Missouri River Basin, projected seasonal declines in precipitation in the southern and western portion of the region are likely to reduce the water available to generate hydropower.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}}
Biofuel feedstocks from crops and forage grown in the Northern Great Plains are vulnerable to climate change, but the net impacts on biofuel production are uncertain.{{< tbib '13' '07b7c06f-35f8-4205-a585-b45e3de00f22' >}}
It is well understood that ground-level ozone (O3) is created by chemical reactions between volatile organic compounds in the presence of sunlight and would be exacerbated by climate change. What is less understood is the sensitivity of regional climate-induced O3 changes, and the science of modeling climate and atmospheric chemistry to understand future conditions.
" uri: /report/nca4/chapter/northern-great-plains/finding/key-message-22-4 url: ~ - chapter_identifier: northern-great-plains confidence: 'There is very high confidence that rising temperature and increases in flooding, runoff events, and drought are likely to lead to increases in impacts to reservations and other Indigenous communities. There is very high confidence that climate changes are already resulting in harmful impacts on tribal economies, livelihoods, and culture. However, the actual impacts and response capacities will depend on the response of regulatory systems and funding amounts.
' evidence: "Multiple lines of research have shown that hydrological changes and changes in extremes have resulted in deleterious impacts to Indigenous peoples.{{< tbib '14' '5f9a3ea9-c2f0-44dc-916a-d3aab217c58d' >}},{{
The chapter lead (CL) and coordinating lead author (CLA) developed a list of potential contributing authors by soliciting suggestions from the past National Climate Assessment (NCA) author team, colleagues and collaborators throughout the region, and contributors to other regional reports. Our initial list of potential authors also included CL nominees submitted to the U.S. Global Change Research Program (USGCRP). The CL and CLA discussed the Northern Great Plains, which was part of the larger Great Plains region for the Third National Climate Assessment (NCA3), with each of these nominees and, as part of that discussion, solicited suggestions for other nominees. This long list of potential contributing authors was pared down by omitting individuals who could not contribute in a timely fashion, and the list was finalized after reconciliation against key themes within the region identified by past NCA authors, the CL and CLA, and contributing author nominees. The team of contributing authors was selected to represent the region geographically and thematically, but participants from some states who had agreed to contribute were eventually unable to do so. Others were unable to contribute from the start. The author team is mostly composed of authors who did not contribute to NCA3.
The CL and CLA, in consultation with past NCA authors and contributing author nominees, identified an initial list of focal areas of regional importance. The author team then solicited input from colleagues and regional experts (identified based on their deep ties to scientific and practitioner communities across the region) on their thoughts on focal areas. This list informed the agenda of a region-wide meeting held on February 22, 2017, with core locations in Fort Collins, Colorado, and Rapid City, South Dakota. The main purpose of this meeting was to seek feedback on the proposed list of focal areas. With this feedback, the author team was able to refine our focal areas to the five themes comprising the Key Messages of the Northern Great Plains regional chapter. Of these, recreation/tourism is a focus area that is new from NCA3.
' report_identifier: nca4 statement: 'Indigenous peoples of the Northern Great Plains are at high risk from a variety of climate change impacts, especially those resulting from hydrological changes, including changes in snowpack, seasonality and timing of precipitation events, and extreme flooding and droughts as well as melting glaciers and reduction in streamflows (likely, very high confidence). These changes are already resulting in harmful impacts to tribal economies, livelihoods, and sacred waters and plants used for ceremonies, medicine, and subsistence (very high confidence). At the same time, many tribes have been very proactive in adaptation and strategic climate change planning (very likely, very high confidence).
' uncertainties: 'The impacts of climate change in the Northern Great Plains are expected to increase risks to Indigenous reservations, communities, and livelihoods. However, there is uncertainty about how Indigenous people will be able to respond. Much of this uncertainty is due to unsettled water rights, multijurisdictional complexities, and federal funding and policies.
' uri: /report/nca4/chapter/northern-great-plains/finding/key-message-22-5 url: ~ - chapter_identifier: southern-great-plains confidence: "The Southern Great Plains will continue to grow rapidly and with high probability of significant competition. Water is the major concern, and political inability to develop a system to allocate water in an equitable manner will continue to build this competitive and contentious issue among all users—energy, food, and water. Quality of life in the region will be compromised as population increases. At least 60% of the region’s population is clustered around urban centers currently, but these population centers are experiencing growth that far exceeds that of rural communities. The remaining population is distributed across vast areas of rural land.{{< tbib '14' 'bf19cfe7-2575-48e2-8d26-b0081117369a' >}},{{
A growing number of adaptation strategies, improved climate services, and early warning decision support systems will more effectively manage the complex regional, national, and transnational issues associated with food, energy, and water. Since a changing climate has significant negative impacts on agriculture in the United States and causes substantial economic costs,{{< tbib '38' '76db17ce-354b-4f0c-ad10-3e701c0387fc' >}} the effects of drought and other occurrences of extreme weather outside the region will also affect the food–energy–water interconnections within the region. (Likely, High confidence)
" evidence: "The connection between food, water, and energy also creates great challenges in the management and distribution of resources. People need food, energy, and water, yet all sectors pull from each other and allocation is a challenge. There are many studies focused on the competitive nature revolving around these resources and the demand by people.{{< tbib '41' '10b9c70e-cabf-44c8-87e7-7905e1fa1e67' >}},{{
The initial Southern Great Plains author team was selected such that expertise from each of the states’ officially recognized climate offices in the region (Kansas, Oklahoma, and Texas) were included. The offices of the state climatologist in Kansas, Oklahoma, and Texas are each members of the American Association of State Climatologists, which is the recognized professional scientific organization for climate expertise at the state level.
One representative from each of several regional hubs of national and regional climate expertise was included on the author team. These regional hubs include the U.S. Department of Agriculture’s Southern Plains Climate Hub (El Reno, Oklahoma), the U.S. Department of the Interior’s South Central Climate Adaptation Science Center (Norman, Oklahoma), and the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessments Southern Climate Impacts Planning Program (Norman, Oklahoma).
After assessing the areas of expertise of the six authors selected from the state and regional centers, a gap analysis was conducted to prioritize areas of expertise that were missing. Due to the importance of the sovereign tribal nations to the Southern Great Plains, an accomplished scholar with expertise in Indigenous knowledge on the environment and climate change was selected from the premier tribal university in the United States, Haskell Indian Nations University in Lawrence, Kansas. An individual from the Environmental Science Institute at the University of Texas at Austin was selected to bring expertise on the complex intersection of coupled atmosphere–land–ocean systems, climate, and humans (population and urbanization). Expertise in the electric utility industry was gained through the Oklahoma Association of Electric Cooperatives by an individual with a long history of working with rural and urban populations and with researchers and forecasters in weather and climate.
The author group decided to allow Southern Great Plains stakeholders to drive additional priorities. On March 2, 2017, the Fourth National Climate Assessment (NCA4) Southern Great Plains chapter team held a Regional Engagement Workshop at the National Weather Center in Norman, Oklahoma, with a satellite location in Austin, Texas, that allowed a number of stakeholders to participate virtually. The objective of the workshop was to gather input from a diverse array of stakeholders throughout the Southern Great Plains to help inform the writing and development of the report and to raise awareness of the process and timeline for NCA4. Stakeholders from meteorology, climatology, tribes, agriculture, electric utilities, water resources, Bureau of Land Management, ecosystems, landscape cooperatives, and transportation from Kansas, Oklahoma, and Texas were represented. The productive dialog at this workshop identified important gaps in environmental economics, ecosystems, and health. Scientists working at the cutting edge of research in these three areas were selected: an ecosystems expert from the Texas Parks and Wildlife Department, an environmental economist from the department of Geography and Environmental Sustainability at the University of Oklahoma, and health experts from the University of Colorado School of Medicine and the Aspen Global Change Institute.
This diverse collection of medical doctors, academics, researchers, scientists, and practitioners from both federal and state agencies gives the Southern Great Plains chapter a wealth of expertise across the many ways in which climate change will affect people in the region.
' report_identifier: nca4 statement: 'Quality of life in the region will be compromised as increasing population, the migration of individuals from rural to urban locations, and a changing climate redistribute demand at the intersection of food consumption, energy production, and water resources (likely, high confidence). A growing number of adaptation strategies, improved climate services, and early warning decision support systems will more effectively manage the complex regional, national, and transnational issues associated with food, energy, and water (likely, high confidence).
' uncertainties: "Research into the intersection of food, energy, and water is in its early stages and historically tends to examine only one or two components.{{< tbib '59' '8a4477fb-8bb9-4b37-8c31-3307f22d84c4' >}},{{
There is very high confidence that extreme heat will increase in frequency and intensity. There is medium confidence in an increased frequency of flooding and high confidence in the increased frequency of drought. There is high confidence of sea level rise of at least 4 feet by 2100 along the Texas coastline if greenhouse gas emissions are not reduced. On the implications for infrastructure, there is high confidence that weather-related damage will increase due to inland weather-related hazards. Along the coastline, there is very high confidence that infrastructure will be impacted by sea level rise and storm surge.
' evidence: "The existing infrastructure and projected models for growth are well established and documented. Demographic and population projections are available from state demographers and are typically included in Long-Term Transportation Plans available from state departments of transportation. Additionally, the present-day infrastructure challenges have been examined in depth by the American Society for Civil Engineers (ASCE), which publishes an Infrastructure Report Card for the Nation and for each state (www.infrastructurereportcard.org).{{< tbib '189' '497411ba-3eb8-42fd-9b01-8c5a21fc6465' >}} For the Southern Great Plains states, one of the pressing concerns is meeting the funding challenges necessary to maintain critical infrastructure, as well as anticipating future revenue streams, which themselves depend on population and its distribution, and state and federal funding. The ASCE, as well as all state transportation plans in the Southern Great Plains, does not consider future climate projections, and the information contained generally does not explicitly mention climate-related stressors. However, the impacts of climate change have become an issue of concern for agencies such as the Department of Transportation (DOT) and Federal Highways Administration (FHWA), which have in recent years funded projects evaluating the potential impacts of climate change on infrastructure and transportation and possible adaptation strategies. Since 2010, the FHWA has sponsored a series of pilot studies in resilience for municipalities and states across the Nation.{{< tbib '190' '93ad29e2-8811-4b6e-854c-fa57408cb570' >}} Two of these studies took place in Texas, in Dallas and Tarrant Counties and in the City of Austin. These reports provide some of the most comprehensive examples of integrating climate data into assessments of infrastructure vulnerability in the region to date. The potential impacts of temperature and precipitation extremes on transportation and infrastructure were based in part on known vulnerabilities as shown by these aforementioned reports and the larger repository of information and resources supplied by the FHWA.
Estimates of relative sea level rise (SLR) in Texas in the historical period are available from NCA4 Volume I: Climate Science Special Report,{{< tbib '24' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} Runkle et al. (2017),{{< tbib '25' '58dfbe91-53a4-4ddb-ad8d-d4e181086e72' >}} Sweet et al. (2017).{{< tbib '191' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} Relative SLR along the Texas coastline is some of the highest in the Nation; coupled with its population and critical energy infrastructure, this region has some noteworthy vulnerabilities to SLR. Projections of SLR remain uncertain and depend to some extent on whether the current rates of relative SLR are maintained, in addition to the magnitude and rate of greenhouse gas emissions. Sweet et al. (2017){{< tbib '191' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}} probabilistically evaluate a number of SLR scenarios, typically noting that the Texas coast SLR is higher than the global mean. The values mentioned in the main text are global mean values obtained from USGCRP (2017){{< tbib '24' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} and from the range quoted by Runkle et al. (2017).{{< tbib '25' '58dfbe91-53a4-4ddb-ad8d-d4e181086e72' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/southern-great-plains/finding/key-message-23-2.yaml identifier: key-message-23-2 ordinal: 2 process: 'The initial Southern Great Plains author team was selected such that expertise from each of the states’ officially recognized climate offices in the region (Kansas, Oklahoma, and Texas) were included. The offices of the state climatologist in Kansas, Oklahoma, and Texas are each members of the American Association of State Climatologists, which is the recognized professional scientific organization for climate expertise at the state level.
One representative from each of several regional hubs of national and regional climate expertise was included on the author team. These regional hubs include the U.S. Department of Agriculture’s Southern Plains Climate Hub (El Reno, Oklahoma), the U.S. Department of the Interior’s South Central Climate Adaptation Science Center (Norman, Oklahoma), and the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessments Southern Climate Impacts Planning Program (Norman, Oklahoma).
After assessing the areas of expertise of the six authors selected from the state and regional centers, a gap analysis was conducted to prioritize areas of expertise that were missing. Due to the importance of the sovereign tribal nations to the Southern Great Plains, an accomplished scholar with expertise in Indigenous knowledge on the environment and climate change was selected from the premier tribal university in the United States, Haskell Indian Nations University in Lawrence, Kansas. An individual from the Environmental Science Institute at the University of Texas at Austin was selected to bring expertise on the complex intersection of coupled atmosphere–land–ocean systems, climate, and humans (population and urbanization). Expertise in the electric utility industry was gained through the Oklahoma Association of Electric Cooperatives by an individual with a long history of working with rural and urban populations and with researchers and forecasters in weather and climate.
The author group decided to allow Southern Great Plains stakeholders to drive additional priorities. On March 2, 2017, the Fourth National Climate Assessment (NCA4) Southern Great Plains chapter team held a Regional Engagement Workshop at the National Weather Center in Norman, Oklahoma, with a satellite location in Austin, Texas, that allowed a number of stakeholders to participate virtually. The objective of the workshop was to gather input from a diverse array of stakeholders throughout the Southern Great Plains to help inform the writing and development of the report and to raise awareness of the process and timeline for NCA4. Stakeholders from meteorology, climatology, tribes, agriculture, electric utilities, water resources, Bureau of Land Management, ecosystems, landscape cooperatives, and transportation from Kansas, Oklahoma, and Texas were represented. The productive dialog at this workshop identified important gaps in environmental economics, ecosystems, and health. Scientists working at the cutting edge of research in these three areas were selected: an ecosystems expert from the Texas Parks and Wildlife Department, an environmental economist from the department of Geography and Environmental Sustainability at the University of Oklahoma, and health experts from the University of Colorado School of Medicine and the Aspen Global Change Institute.
This diverse collection of medical doctors, academics, researchers, scientists, and practitioners from both federal and state agencies gives the Southern Great Plains chapter a wealth of expertise across the many ways in which climate change will affect people in the region.
' report_identifier: nca4 statement: 'The built environment is vulnerable to increasing temperature, extreme precipitation, and continued sea level rise, particularly as infrastructure ages and populations shift to urban centers (likely, high confidence). Along the Texas Gulf Coast, relative sea level rise of twice the global average will put coastal infrastructure at risk (likely, medium confidence). Regional adaptation efforts that harden or relocate critical infrastructure will reduce the risk of climate change impacts.
' uncertainties: "In the Southern Great Plains there remains uncertainty over the direction of change of average precipitation, although models generally project increases in very heavy precipitation.{{< tbib '1' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} The expectation of an increase in the frequency of events such as the 100-year storm is uncertain due to the spread of model projections of extreme precipitation and the need to use additional statistical modeling in order to obtain the return period estimates.
There are limited studies that attempt to directly link weather and climate extremes and their impacts to infrastructure. While it is appreciated that infrastructure exposed to adverse conditions will lead to deterioration, studies on specific cause–effect chain of events in these cases are limited (e.g., Winguth et al. 2015){{< tbib '192' '3fed1df6-1ec6-4f8b-a3b7-6bb715cee3ee' >}}. The results are more evident in the case of catastrophic failures associated with floods, for example, but even in those cases, antecedent conditions related to the age, condition, and/or construction quality of infrastructure will affect its resilience (Ch. 12: Transportation;).
" uri: /report/nca4/chapter/southern-great-plains/finding/key-message-23-2 url: ~ - chapter_identifier: southern-great-plains confidence: 'There is high confidence that rising temperatures and increases in flooding, runoff events, and aridity will likely lead to changes in the aquatic and terrestrial habitats supporting many regional species. Flooding has changed the complexity of many riparian habitats. Increases already seen in extreme drought occurrence have caused downturns in the fish- and wildlife-related industries, with losses in traditional fish (crab and oysters) and wildlife species (waterfowl) important for both recreational and commercial purposes.
In contrast, habitat created by invasive species due to climate change has improved populations of other species including fungi. The expanded stress due to a rapidly growing population in this region increases the likelihood (high confidence) of negative natural resource and ecosystems outcomes in the future.
' evidence: "This Key Message was developed through technical discussions developed within science teams and collaborators of the Gulf Coast and Great Plains Landscape Conservation Cooperatives. Species’ response to climate change is complex and variable;{{< tbib '119' '506759aa-765f-4007-a678-17d69d139e39' >}} this complexity necessitates a multifaceted review of the projected impacts of climate change. In addition, ecosystem services also require assessment, given the impact of climate change on their ability to deliver materials and processes that benefit people.{{< tbib '123' 'c3b02b08-e555-4a41-8a73-8b04dc89ee6b' >}}
The following relevant areas of evidence regarding climate change impacts on ecosystems in the Southern Great Plains were therefore considered: species, aquatic ecosystems, coastal bays and estuaries, and risk management. It is unclear how climate change will affect species directly, but the effects of increased aridity will likely have negative impacts (e.g., NFWPCAP 2012{{< tbib '123' 'c3b02b08-e555-4a41-8a73-8b04dc89ee6b' >}}). Species migration (e.g., Schmandt 2011{{< tbib '126' '373310ba-0499-4640-8a23-211736f3b32d' >}}) and mortality (e.g., Moore et al 2016{{< tbib '127' 'f1380bfc-e39d-43d9-87d6-dfcff35fa7fb' >}}) will increase in response to climate change. Climate change impacts to aquatic ecosystems include higher water temperatures in lakes, wetlands, rivers, and estuaries, while impacts to reservoirs include fluctuating lake levels, loss of habitat, loss of recreational access, increase in harmful algal blooms, and disconnectedness from upstream and downstream riverine habitat.{{< tbib '129' '9bff2ebb-6418-481a-bad9-b8c29875286e' >}} Sea level rise will impact coastal bays and estuaries via more frequent and longer-lasting flooding of marshes,{{< tbib '126' '373310ba-0499-4640-8a23-211736f3b32d' >}},{{
The initial Southern Great Plains author team was selected such that expertise from each of the states’ officially recognized climate offices in the region (Kansas, Oklahoma, and Texas) were included. The offices of the state climatologist in Kansas, Oklahoma, and Texas are each members of the American Association of State Climatologists, which is the recognized professional scientific organization for climate expertise at the state level.
One representative from each of several regional hubs of national and regional climate expertise was included on the author team. These regional hubs include the U.S. Department of Agriculture’s Southern Plains Climate Hub (El Reno, Oklahoma), the U.S. Department of the Interior’s South Central Climate Adaptation Science Center (Norman, Oklahoma), and the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessments Southern Climate Impacts Planning Program (Norman, Oklahoma).
After assessing the areas of expertise of the six authors selected from the state and regional centers, a gap analysis was conducted to prioritize areas of expertise that were missing. Due to the importance of the sovereign tribal nations to the Southern Great Plains, an accomplished scholar with expertise in Indigenous knowledge on the environment and climate change was selected from the premier tribal university in the United States, Haskell Indian Nations University in Lawrence, Kansas. An individual from the Environmental Science Institute at the University of Texas at Austin was selected to bring expertise on the complex intersection of coupled atmosphere–land–ocean systems, climate, and humans (population and urbanization). Expertise in the electric utility industry was gained through the Oklahoma Association of Electric Cooperatives by an individual with a long history of working with rural and urban populations and with researchers and forecasters in weather and climate.
The author group decided to allow Southern Great Plains stakeholders to drive additional priorities. On March 2, 2017, the Fourth National Climate Assessment (NCA4) Southern Great Plains chapter team held a Regional Engagement Workshop at the National Weather Center in Norman, Oklahoma, with a satellite location in Austin, Texas, that allowed a number of stakeholders to participate virtually. The objective of the workshop was to gather input from a diverse array of stakeholders throughout the Southern Great Plains to help inform the writing and development of the report and to raise awareness of the process and timeline for NCA4. Stakeholders from meteorology, climatology, tribes, agriculture, electric utilities, water resources, Bureau of Land Management, ecosystems, landscape cooperatives, and transportation from Kansas, Oklahoma, and Texas were represented. The productive dialog at this workshop identified important gaps in environmental economics, ecosystems, and health. Scientists working at the cutting edge of research in these three areas were selected: an ecosystems expert from the Texas Parks and Wildlife Department, an environmental economist from the department of Geography and Environmental Sustainability at the University of Oklahoma, and health experts from the University of Colorado School of Medicine and the Aspen Global Change Institute.
This diverse collection of medical doctors, academics, researchers, scientists, and practitioners from both federal and state agencies gives the Southern Great Plains chapter a wealth of expertise across the many ways in which climate change will affect people in the region.
' report_identifier: nca4 statement: 'Terrestrial and aquatic ecosystems are being directly and indirectly altered by climate change (likely, high confidence). Some species can adapt to extreme droughts, unprecedented floods, and wildfires from a changing climate, while others cannot, resulting in significant impacts to both services and people living in these ecosystems (likely, high confidence). Landscape-scale ecological services will increase the resilience of the most vulnerable species.
' uncertainties: "Ecosystems and the species that exist in these ecosystems have experienced a rapid decline in many “common species” as well as certain rare species.{{< tbib '123' 'c3b02b08-e555-4a41-8a73-8b04dc89ee6b' >}},{{
There is very high confidence that rising temperatures and changes in precipitation leading to flooding, runoff events, and aridity will likely lead to negative impacts on human health in the Southern Great Plains. There is high confidence that certain populations, such as very young and old and socioeconomically disadvantaged individuals, will likely be disproportionately affected.
' evidence: "This Key Message was developed in close coordination with the Human Health (Ch. 14) author team and incorporated applicable inputs from the U.S. Climate and Health Assessment.{{< tbib '168' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} Multiple lines of evidence demonstrate statistically significant associations between temperature, precipitation, and other climatologic variables with adverse health outcomes, including heat-related illness, respiratory disease, malnutrition, and vector-borne disease.{{< tbib '168' 'f1e633d5-070a-4a7d-935b-a2281a0c9cb6' >}} Regionally specific examples of these well-documented impacts were identified through literature reviews conducted to identify regionally specific studies of these impacts.
There is strong evidence that increasing average temperatures as well as increasing frequency, duration, and intensity of extreme heat events will occur in the Southern Great Plains by the middle and end of this century, with higher CO2 emissions leading to greater and faster temperature increases.{{< tbib '80' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}} Extreme temperatures are shown with high confidence to have substantial effects on morbidity and mortality {{< tbib '142' 'e337db11-d5e9-4a9b-be9f-7773befd61b9' >}},{{
Climate change is expected (with medium to high confidence) to increase the frequency of extreme rainfall and hurricanes, although impacts in the Southern Great Plains remain difficult to quantify.{{< tbib '2' '52ce1b63-1b04-4728-9f1b-daee39af665e' >}} The Gulf Coast of Texas in particular has experienced several record-breaking floods and tropical cyclones in recent years, including Hurricane Harvey. Hurricanes and resultant flooding result in significant health impacts, including deaths from drowning and trauma, critical shortages of essential medications, critical healthcare system power shortages, and forced patient evacuations.{{< tbib '9' 'b5bf5f25-1fd9-43bd-8493-0ef2ee771f47' >}} Such events strain healthcare resources not only within regions of direct hurricane impact but also within the entire region due to displacement of patient populations.{{< tbib '8' 'f8225523-7ae9-4ab4-ac28-4cfafe1b508b' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/southern-great-plains/finding/key-message-23-4.yaml identifier: key-message-23-4 ordinal: 4 process: 'The initial Southern Great Plains author team was selected such that expertise from each of the states’ officially recognized climate offices in the region (Kansas, Oklahoma, and Texas) were included. The offices of the state climatologist in Kansas, Oklahoma, and Texas are each members of the American Association of State Climatologists, which is the recognized professional scientific organization for climate expertise at the state level.
One representative from each of several regional hubs of national and regional climate expertise was included on the author team. These regional hubs include the U.S. Department of Agriculture’s Southern Plains Climate Hub (El Reno, Oklahoma), the U.S. Department of the Interior’s South Central Climate Adaptation Science Center (Norman, Oklahoma), and the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessments Southern Climate Impacts Planning Program (Norman, Oklahoma).
After assessing the areas of expertise of the six authors selected from the state and regional centers, a gap analysis was conducted to prioritize areas of expertise that were missing. Due to the importance of the sovereign tribal nations to the Southern Great Plains, an accomplished scholar with expertise in Indigenous knowledge on the environment and climate change was selected from the premier tribal university in the United States, Haskell Indian Nations University in Lawrence, Kansas. An individual from the Environmental Science Institute at the University of Texas at Austin was selected to bring expertise on the complex intersection of coupled atmosphere–land–ocean systems, climate, and humans (population and urbanization). Expertise in the electric utility industry was gained through the Oklahoma Association of Electric Cooperatives by an individual with a long history of working with rural and urban populations and with researchers and forecasters in weather and climate.
The author group decided to allow Southern Great Plains stakeholders to drive additional priorities. On March 2, 2017, the Fourth National Climate Assessment (NCA4) Southern Great Plains chapter team held a Regional Engagement Workshop at the National Weather Center in Norman, Oklahoma, with a satellite location in Austin, Texas, that allowed a number of stakeholders to participate virtually. The objective of the workshop was to gather input from a diverse array of stakeholders throughout the Southern Great Plains to help inform the writing and development of the report and to raise awareness of the process and timeline for NCA4. Stakeholders from meteorology, climatology, tribes, agriculture, electric utilities, water resources, Bureau of Land Management, ecosystems, landscape cooperatives, and transportation from Kansas, Oklahoma, and Texas were represented. The productive dialog at this workshop identified important gaps in environmental economics, ecosystems, and health. Scientists working at the cutting edge of research in these three areas were selected: an ecosystems expert from the Texas Parks and Wildlife Department, an environmental economist from the department of Geography and Environmental Sustainability at the University of Oklahoma, and health experts from the University of Colorado School of Medicine and the Aspen Global Change Institute.
This diverse collection of medical doctors, academics, researchers, scientists, and practitioners from both federal and state agencies gives the Southern Great Plains chapter a wealth of expertise across the many ways in which climate change will affect people in the region.
' report_identifier: nca4 statement: 'Health threats, including heat illness and diseases transmitted through food, water, and insects, will increase as temperature rises (very likely, high confidence). Weather conditions supporting these health threats are projected to be of longer duration or occur at times of the year when these threats are not normally experienced (likely, medium confidence). Extreme weather events with resultant physical injury and population displacement are also a threat (likely, high confidence). These threats are likely to increase in frequency and distribution and are likely to create significant economic burdens (likely, high confidence). Vulnerability and adaptation assessments, comprehensive response plans, seasonal health forecasts, and early warning systems can be useful adaptation strategies.
' uncertainties: 'The ability to quantitatively predict specific health outcomes associated with projected changes in climate is limited by long-term public health data as well as meteorological data. While assessments consistently indicate that climate change will have direct and indirect impacts on human health (high confidence), quantifying specific health metrics, such as incidence and community level prevalence, remains difficult. The uncertainty develops when there are many connected actions that influence health outcomes. For example, the future impact of climate change on human health is likely to be reduced by adaptation measures that take place on local and national scales. Additionally, the role of non-climate factors, including land use, socioeconomics, and population characteristics (such as immigration), as well as health sector policies and practices, will affect local and regional health impacts. The magnitude of impact of these variables on health at local and regional scales is difficult to predict. The estimation of future economic impacts is limited by difficulties in estimating the true cost of healthcare delivery and additionally only partially captures the actual impacts on health and livelihood of individuals and communities. Thus, existing projections likely underestimate the entirety of the economic impact.
' uri: /report/nca4/chapter/southern-great-plains/finding/key-message-23-4 url: ~ - chapter_identifier: southern-great-plains confidence: 'There is high confidence that extreme events and long-term climate shifts will lead to changes in tribal and Indigenous communities in the Southern Great Plains. Environmental connections will be direct, but the degree of those connections is uncertain and shifts in climate system will impact each nation differently. How changes will be perceived and managed and what steps are taken to adapt are uncertain; thus, there is low confidence that adaptation will be a successful mechanism among all tribal and Indigenous peoples.
' evidence: "This Key Message was developed through dialog and discussions among Indigenous communities and within the social sciences discipline. While Indigenous communities vary in size from smaller nations to large well-formed governments, all are in need of communication about the realities of climate change.{{< tbib '14' 'bf19cfe7-2575-48e2-8d26-b0081117369a' >}} Climate change threatens the ability of tribes and Indigenous peoples to procure food, water, and shelter and to preserve ancient cultural activities.{{< tbib '179' '64063229-e3bd-4ab7-ba73-41909ca78211' >}},{{
The initial Southern Great Plains author team was selected such that expertise from each of the states’ officially recognized climate offices in the region (Kansas, Oklahoma, and Texas) were included. The offices of the state climatologist in Kansas, Oklahoma, and Texas are each members of the American Association of State Climatologists, which is the recognized professional scientific organization for climate expertise at the state level.
One representative from each of several regional hubs of national and regional climate expertise was included on the author team. These regional hubs include the U.S. Department of Agriculture’s Southern Plains Climate Hub (El Reno, Oklahoma), the U.S. Department of the Interior’s South Central Climate Adaptation Science Center (Norman, Oklahoma), and the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessments Southern Climate Impacts Planning Program (Norman, Oklahoma).
After assessing the areas of expertise of the six authors selected from the state and regional centers, a gap analysis was conducted to prioritize areas of expertise that were missing. Due to the importance of the sovereign tribal nations to the Southern Great Plains, an accomplished scholar with expertise in Indigenous knowledge on the environment and climate change was selected from the premier tribal university in the United States, Haskell Indian Nations University in Lawrence, Kansas. An individual from the Environmental Science Institute at the University of Texas at Austin was selected to bring expertise on the complex intersection of coupled atmosphere–land–ocean systems, climate, and humans (population and urbanization). Expertise in the electric utility industry was gained through the Oklahoma Association of Electric Cooperatives by an individual with a long history of working with rural and urban populations and with researchers and forecasters in weather and climate.
The author group decided to allow Southern Great Plains stakeholders to drive additional priorities. On March 2, 2017, the Fourth National Climate Assessment (NCA4) Southern Great Plains chapter team held a Regional Engagement Workshop at the National Weather Center in Norman, Oklahoma, with a satellite location in Austin, Texas, that allowed a number of stakeholders to participate virtually. The objective of the workshop was to gather input from a diverse array of stakeholders throughout the Southern Great Plains to help inform the writing and development of the report and to raise awareness of the process and timeline for NCA4. Stakeholders from meteorology, climatology, tribes, agriculture, electric utilities, water resources, Bureau of Land Management, ecosystems, landscape cooperatives, and transportation from Kansas, Oklahoma, and Texas were represented. The productive dialog at this workshop identified important gaps in environmental economics, ecosystems, and health. Scientists working at the cutting edge of research in these three areas were selected: an ecosystems expert from the Texas Parks and Wildlife Department, an environmental economist from the department of Geography and Environmental Sustainability at the University of Oklahoma, and health experts from the University of Colorado School of Medicine and the Aspen Global Change Institute.
This diverse collection of medical doctors, academics, researchers, scientists, and practitioners from both federal and state agencies gives the Southern Great Plains chapter a wealth of expertise across the many ways in which climate change will affect people in the region.
' report_identifier: nca4 statement: 'Tribal and Indigenous communities are particularly vulnerable to climate change due to water resource constraints, extreme weather events, higher temperature, and other likely public health issues (likely, high confidence). Efforts to build community resilience can be hindered by economic, political, and infrastructure limitations (likely, high confidence), but traditional knowledge and intertribal organizations provide opportunities to adapt to the potential challenges of climate change.
' uncertainties: "There is a great deal of uncertainty regarding how tribal communities will integrate climate change into their cultures, given the variable size of these communities and the challenges of connecting and communicating with clarity among them. It is likely that adaptation strategies will vary greatly as knowledge and communication might not be widely supported within all nations.{{< tbib '169' '60233f20-d45f-4086-ada7-00dbd47712c3' >}},{{
There is high confidence that climate change, through reductions in snowpack, increased temperatures, and more variable precipitation, is already affecting the Northwest’s diverse natural resource base. There is high confidence that these natural resource sectors provide critical economic benefits, particularly for rural, tribal, and Indigenous communities who are more dependent on economic activities associated with natural resource management. There is high confidence that climate change will have a large impact on the natural resource sector throughout this century; however, there is medium confidence that these impacts will negatively impact rural, tribal, and Indigenous livelihoods, particularly about how projected changes will economically impact specific natural resource sectors due to large uncertainties surrounding global market dynamics that are influenced by climatic and non-climatic factors. It is very likely that proactive management efforts will be required to reduce climate risks, yet there is medium confidence that these adaptation efforts will adequately reduce negative impacts and promote sector-specific economic benefits.
' evidence: "Multiple studies suggest that Northwest natural resource sectors will likely be directly affected by climate change, including increased temperatures, changes in precipitation patterns, and reduced snowpack (see NOAA State Climate Summaries for Oregon, Washington, and Idaho).{{< tbib '265' 'ba49da5a-489b-420e-b593-8d83e4fbf5a5' >}},{{
There is good evidence that natural resource managers are attempting to build more resilient production systems in the face of climate change through the adoption of adaptation practices (see Box 24.1), particularly those that build soil resources to increase resilience in the face of more extreme and variable weather; however, in some cases not all adaptation strategies will necessarily lead to broader soil benefits.{{< tbib '270' '2a6fd72f-138b-46d2-9f9e-26277d961c13' >}},{{
Yet, how individual actors respond to changes in climate is a source of uncertainty, particularly if these actions do not reduce climate risks or capitalize on potential benefits as expected.{{< tbib '64' 'daa849df-9a29-44ee-b59c-9b4b5fd53467' >}} Additionally, many adaptive actions, at least in the short term, will likely be costly for individual producers to implement.{{< tbib '37' '28a86b7f-c68a-4d17-bd11-083814d9ed27' >}},{{
This assessment focuses on different aspects of the interaction between humans, the natural environment, and climate change, including reliance on natural resources for livelihoods, the less tangible values of nature, the built environment, health, and frontline communities. Therefore, the author team required a depth and breadth of expertise that went beyond climate change science and included social science, economics, health, tribes and Indigenous people, frontline communities, and climate adaptation, as well as expertise in agriculture, forestry, hydrology, coastal and ocean dynamics, and ecology. Prospective authors were nominated by their respective agencies, universities, organizations, or peers. All prospective authors were interviewed with respect to the qualifications, and selected authors committed to remain part of the team for the duration of chapter development.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at workshops, weekly teleconferences, and email exchanges. The author team, along with the U.S. Global Change Research Program (USGCRP), also held stakeholder meetings in Portland and Boise to solicit input and receive feedback on the outline and draft content under consideration. A series of breakout groups during the stakeholder meetings provided invaluable feedback that is directly reflected in how the Key Messages were shaped with respect to Northwest values and the intersection between humans, the natural environment, and climate change. The authors also considered inputs and comments submitted by the public, interested stakeholders, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations during multiple exchanges with contributing authors for other chapters, who provided additional expertise on subsets of the Traceable Accounts associated with each Key Message.
The climate change projections and scenarios used in this assessment have been widely examined and presented elsewhere{{< tbib '11' '07aed96a-e0e8-47dd-81d3-cdff5a6e261c' >}},{{
Climate change is already affecting the Northwest’s diverse natural resources (high confidence), which support sustainable livelihoods; provide a robust foundation for rural, tribal, and Indigenous communities; and strengthen local economies (high confidence). Climate change is expected to continue affecting the natural resource sector (likely, high confidence), but the economic consequences will depend on future market dynamics, management actions, and adaptation efforts (very likely, medium confidence). Proactive management can increase the resilience of many natural resources and their associated economies (very likely, medium confidence).
' uncertainties: "Climate impacts, such as increased temperatures, reduced snowpack, and more variable precipitation and subsequent impacts on pests, disease, fire incidence, and other secondary impacts will very likely indirectly affect livelihoods and the economic viability of natural resource sectors, with more severe impacts to rural, tribal, and Indigenous communities (Ch. 10: Ag & Rural). There is, however, greater uncertainty as to how precisely these impacts are projected to affect natural resource managers’ financial security and their subsequent land-use decisions (Ch. 5: Land Changes), as well as other factors important to sustainable livelihoods and community well-being.
This is particularly relevant for key commodities that are integrated with national and international markets that are influenced by multiple factors and are difficult to predict (Ch. 10: Ag & Rural; Ch. 16: International). National and global market dynamics will likely be influenced by broader climate change effects on other natural resource sectors in the United States and across the globe,{{< tbib '50' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}} while also being impacted by a broad array of factors that include technological developments, laws, regulations and policies affecting trade and subsidies, and security issues. There are instances where the economic consequences will likely be positive, particularly in comparison to other regions in the United States, such as found in the dairy production sector.{{< tbib '65' '4c87b5a3-0303-4f92-ae7b-97d5e20b9579' >}} The economic impacts to regional fisheries are much less certain as iconic species and industries in the Northwest struggle to maintain viability.{{< tbib '51' 'bfd896fb-e6cf-45bb-90fc-46742079789c' >}},{{
There is high confidence that climate change and extreme events have already endangered the well-being of a wide range of wildlife, fish, and plants. There is very high confidence that these impacts will directly threaten tribal subsistence and culture and high confidence that these impacts will threaten popular recreation activities. Future climate change will very likely continue to have adverse impacts on the regional environment. There is high confidence that future climate change will have negative impacts on the values, identity, heritage, cultures, and quality of life of the diverse population of Northwest residents. There is medium confidence that adaptation and informed management, especially culturally appropriate strategies, will increase the resilience of the region’s natural capital.
' evidence: "Since the Third National Climate Assessment, there have been significant contributions within the literature in relation to climate impacts to Northwest communities, with specific focus on how values and activities, such as recreation, iconic wildlife, management, and tribal and Indigenous cultures, will likely be impacted.
Wildlife are projected to have diverse responses to climate change.{{< tbib '94' '28638cf2-7042-48cf-8a30-7f45b405aefb' >}},{{
Multiple studies also demonstrate that climate change impacts will likely affect other iconic, Northwest species. Wildfires will affect berries, roots, and plants;{{< tbib '85' '6848eec2-534b-4629-967c-53d8530089a3' >}},{{
Salmon is one of the most iconic Northwest species and important First Foods for Tribes. Salmon are at high risk to climate change because of decreasing summer flows due to changes in seasonal precipitation and reduced snowpack,{{< tbib '284' 'f8d978b8-85d3-47ea-9a90-543650d83156' >}},{{
There are multiple lines of evidence verifying that reduced snowfall and snowpack in the future will adversely impact winter and snow-based recreation, including a reduction in ski visitation rates.{{< tbib '19' 'b1729fa8-3fbf-4311-a2d0-e0b36ccb9fb6' >}},{{
Adaptation and management strategies in response to climate impacts on the natural capital and Northwest heritage are extremely varied across the region. Many tribes have begun managing First Foods and other important cultural resources through climate change vulnerability assessments and adaptation plans that incorporate both traditional knowledge and western science.{{< tbib '85' '6848eec2-534b-4629-967c-53d8530089a3' >}},{{
This assessment focuses on different aspects of the interaction between humans, the natural environment, and climate change, including reliance on natural resources for livelihoods, the less tangible values of nature, the built environment, health, and frontline communities. Therefore, the author team required a depth and breadth of expertise that went beyond climate change science and included social science, economics, health, tribes and Indigenous people, frontline communities, and climate adaptation, as well as expertise in agriculture, forestry, hydrology, coastal and ocean dynamics, and ecology. Prospective authors were nominated by their respective agencies, universities, organizations, or peers. All prospective authors were interviewed with respect to the qualifications, and selected authors committed to remain part of the team for the duration of chapter development.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at workshops, weekly teleconferences, and email exchanges. The author team, along with the U.S. Global Change Research Program (USGCRP), also held stakeholder meetings in Portland and Boise to solicit input and receive feedback on the outline and draft content under consideration. A series of breakout groups during the stakeholder meetings provided invaluable feedback that is directly reflected in how the Key Messages were shaped with respect to Northwest values and the intersection between humans, the natural environment, and climate change. The authors also considered inputs and comments submitted by the public, interested stakeholders, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations during multiple exchanges with contributing authors for other chapters, who provided additional expertise on subsets of the Traceable Accounts associated with each Key Message.
The climate change projections and scenarios used in this assessment have been widely examined and presented elsewhere{{< tbib '11' '07aed96a-e0e8-47dd-81d3-cdff5a6e261c' >}},{{
Climate change and extreme events are already endangering the well-being of a wide range of wildlife, fish, and plants (high confidence), which are intimately tied to tribal subsistence culture (very high confidence) and popular outdoor recreation activities (high confidence). Climate change is projected to continue to have adverse impacts on the regional environment (very likely), with implications for the values, identity, heritage, cultures, and quality of life of the region’s diverse population (high confidence). Adaptation and informed management, especially culturally appropriate strategies, will likely increase the resilience of the region’s natural capital (medium confidence).
' uncertainties: "There is strong evidence to suggest that recreational opportunities are an important quality of the Northwest,{{< tbib '87' '7a666151-302c-4d04-9658-b80816eeec98' >}} but there is uncertainty around the perceived importance of future recreation opportunities’ prioritization in people’s quality of life despite the direct reduction of many recreational opportunities.{{< tbib '127' '84baf9f1-d4b2-491f-8bde-d03168080fa5' >}}
The effects of climate change on game species are uncertain, with large potential forcing in both directions and a lack of information on which processes will dominate consequences for game species and how managers might be able to effectively adapt to changing climate.
" uri: /report/nca4/chapter/northwest/finding/key-message-24-2 url: ~ - chapter_identifier: northwest confidence: "There is very high confidence in the link between extreme events and infrastructure impacts. Most of the existing vulnerability assessments in this region, as well as those at larger spatial scales, emphasize extreme events as a key driver of past impacts. Most infrastructure is planned and designed to withstand events of a specified frequency and magnitude (for example, the 100-year flood, design storms), underscoring the importance of extreme events to our assumptions about infrastructure reliability and function. There is high confidence that rising temperatures, increases in heavy rainfall, and hydrologic changes are projected for the region.{{< tbib '5' 'e450ba2c-db69-43c8-8af4-e0c8ce7c8f2f' >}},{{
Impacts discussed in this chapter (e.g., WSDOT 2014, ODOT and OHA 2016, Withycomb 2017, US Climate Resilience Toolkit 2017{{< tbib '129' 'ce288ad6-4610-400a-805b-fc5e59d20c32' >}},{{
There is a growing body of evidence suggesting that climate change will likely increase the frequency and/or intensity of extreme events such as flooding, landslides, drought, wildfire, and heat waves.{{< tbib '27' '2ca19a87-6e16-41d2-8767-19767e5a74d1' >}},{{
Infrastructure redundancy is widely accepted as a means to enhance system reliability. Multiple investigations cite the importance of system redundancy for transportation, energy, and water supply.{{< tbib '136' '3dd8a56b-03bf-40b4-8b09-6d202e75e901' >}},{{
This assessment focuses on different aspects of the interaction between humans, the natural environment, and climate change, including reliance on natural resources for livelihoods, the less tangible values of nature, the built environment, health, and frontline communities. Therefore, the author team required a depth and breadth of expertise that went beyond climate change science and included social science, economics, health, tribes and Indigenous people, frontline communities, and climate adaptation, as well as expertise in agriculture, forestry, hydrology, coastal and ocean dynamics, and ecology. Prospective authors were nominated by their respective agencies, universities, organizations, or peers. All prospective authors were interviewed with respect to the qualifications, and selected authors committed to remain part of the team for the duration of chapter development.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at workshops, weekly teleconferences, and email exchanges. The author team, along with the U.S. Global Change Research Program (USGCRP), also held stakeholder meetings in Portland and Boise to solicit input and receive feedback on the outline and draft content under consideration. A series of breakout groups during the stakeholder meetings provided invaluable feedback that is directly reflected in how the Key Messages were shaped with respect to Northwest values and the intersection between humans, the natural environment, and climate change. The authors also considered inputs and comments submitted by the public, interested stakeholders, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations during multiple exchanges with contributing authors for other chapters, who provided additional expertise on subsets of the Traceable Accounts associated with each Key Message.
The climate change projections and scenarios used in this assessment have been widely examined and presented elsewhere{{< tbib '11' '07aed96a-e0e8-47dd-81d3-cdff5a6e261c' >}},{{
Existing water, transportation, and energy infrastructure already face challenges from flooding, landslides, drought, wildfire, and heat waves (very high confidence). Climate change is projected to increase the risks from many of these extreme events, potentially compromising the reliability of water supplies, hydropower, and transportation across the region (likely, high confidence). Isolated communities and those with systems that lack redundancy are the most vulnerable (likely, medium confidence). Adaptation strategies that address more than one sector, or are coupled with social and environmental co-benefits, can increase resilience (high confidence).
' uncertainties: 'Many analyses and anecdotal evidence link the risk of infrastructure disruption or failure to extreme events. However, the attribution of specific infrastructure impacts to climate variability or climate change remains a challenge. In many cases, infrastructure is subject to multiple climate and non-climate stressors. Non-climate stressors common to many parts of the region include increases in demand or usage from growing populations and changes in land use or development. In addition, much infrastructure across the region is beyond its useful lifetime or may not be in a state of good repair. These factors typically enhance sensitivity to many types of stressors but add uncertainty when trying to draw a direct connection between climate and infrastructure impacts.
Demographic shifts remain an important uncertainty when assessing future infrastructure impacts as well as the relative importance of certain types of infrastructure. Migration to and within the region can fluctuate on timescales shorter than those of climate change. As people move, the relative importance of different types of infrastructure are likely to change, as are the consequences of impacts.
Lastly, there is considerable uncertainty in quantitatively assessing the role of redundancy in minimizing or managing impacts. Metrics for determining the extent to which networking or emergency/backup systems yield adaptive capacity are not currently available at the regional scale.
' uri: /report/nca4/chapter/northwest/finding/key-message-24-3 url: ~ - chapter_identifier: northwest confidence: 'There is high confidence that there will be increased hazards and epidemics, which will very likely disrupt local economies, food systems, and exacerbate chronic health risks, especially among populations most at risk. There is high confidence that these acute hazards will increase due to future climate conditions and will very likely increase the demand on organizations and volunteers that respond and form the region’s social safety net. There is medium confidence that mitigation investments can help counterbalance these risks and likely result in health co-benefits for the region.
' evidence: "Cascading hazards could occur in any season; however, the summer months pose the biggest health challenges. For example, wildfire could occur at the same time as extreme heat and could damage electrical distribution systems, thereby simultaneously exposing people to smoke and high temperatures without the ability to pump water, filter air, or control indoor temperatures. Although some work is being done to prepare, responses to emergency incidents continue to show that there are considerable gaps in our medical and public health systems.{{< tbib '315' '4774f70f-d9c5-43a7-9561-ef771165e5b9' >}} Public health departments are in place to track, monitor, predict, and develop response tactics to disease outbreaks or other health threats. In the case of cascading hazards, the public health system has a role in communicating risks to the public as well as strategies for self-care and sheltering-in-place during a crisis. Unfortunately, local health departments report inadequate capacity to respond to local climate change-related health threats, mainly due to budget constraints.{{< tbib '316' 'f82a2e76-95bb-4a33-8877-8c16ca217397' >}} Hospitals in the United States routinely operate at or above capacity. Large numbers of emergency rooms are crowded with admitted patients awaiting placement in inpatient beds, and hospitals are diverting more than half a million ambulances per year due to emergency room overcrowding.{{< tbib '317' '3c69fb3a-7bcd-4acb-93a2-5dbf687d8491' >}}
Existing environmental health risks are expected to be exacerbated by future climate conditions,{{< tbib '187' 'b1577125-f789-49e6-9656-c40ed932184a' >}} yet over 95% of local health departments in Oregon reported having only partial-to-minimal ability to identify and address environmental health hazards.{{< tbib '194' '796714bc-3fbc-471a-9c93-fbee657006a9' >}} The capacity of our public health systems is largely inadequate and unable to meet basic responsibilities to protect the health and safety of people in the Northwest.{{< tbib '162' 'f1ca2352-7158-4312-9c4b-3d1189c1ad10' >}},{{
Socioeconomic income levels can be a predictor of environmental health outcomes in the future.{{< tbib '187' 'b1577125-f789-49e6-9656-c40ed932184a' >}},{{
Climate mitigation strategies can in some cases have substantial health co-benefits, with evidence pointing toward active transportation{{< tbib '319' '50e17b29-8313-4a48-95e9-cdca2241f4ea' >}} and green infrastructure improvements.{{< tbib '320' 'd1845478-f491-4533-8ef3-bad72ef5282d' >}} This evidence of health co-benefits provides an additional and immediate rationale for reductions in greenhouse gas emissions beyond that of climate change mitigation alone. Recognition that mitigation strategies can have substantial benefits for both health and climate protection offers the possibility of strategies that are potentially both more cost effective and socially attractive than are those that address these priorities independently.{{< tbib '321' '25181456-7f49-4348-8ce8-55e4def0e02b' >}} The Oregon Health Authority’s Climate Smart Strategy Health Impact Assessment found that almost all climate mitigation policies under consideration by the Metro Regional Government could improve health, and that certain policy combinations were more beneficial, namely those that reduced vehicle miles traveled.{{< tbib '322' '62f522a8-bb4a-44a3-89a4-2862e6cd2981' >}} For example, according to 2009 data available on the National Environmental Public Health Tracking Network, a 10% reduction in PM2.5 could prevent more than 400 deaths per year in a highly populated county and about 1,500 deaths every year in the state of California alone. Working across sectors to incorporate a health promotion approach in the design and development of built environment components could mitigate climate change, promote adaptation, and improve public health.{{< tbib '323' 'd01a3234-774c-4ea8-bbc3-f7fd726699bb' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/northwest/finding/key-message-24-4.yaml identifier: key-message-24-4 ordinal: 4 process: "This assessment focuses on different aspects of the interaction between humans, the natural environment, and climate change, including reliance on natural resources for livelihoods, the less tangible values of nature, the built environment, health, and frontline communities. Therefore, the author team required a depth and breadth of expertise that went beyond climate change science and included social science, economics, health, tribes and Indigenous people, frontline communities, and climate adaptation, as well as expertise in agriculture, forestry, hydrology, coastal and ocean dynamics, and ecology. Prospective authors were nominated by their respective agencies, universities, organizations, or peers. All prospective authors were interviewed with respect to the qualifications, and selected authors committed to remain part of the team for the duration of chapter development.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at workshops, weekly teleconferences, and email exchanges. The author team, along with the U.S. Global Change Research Program (USGCRP), also held stakeholder meetings in Portland and Boise to solicit input and receive feedback on the outline and draft content under consideration. A series of breakout groups during the stakeholder meetings provided invaluable feedback that is directly reflected in how the Key Messages were shaped with respect to Northwest values and the intersection between humans, the natural environment, and climate change. The authors also considered inputs and comments submitted by the public, interested stakeholders, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations during multiple exchanges with contributing authors for other chapters, who provided additional expertise on subsets of the Traceable Accounts associated with each Key Message.
The climate change projections and scenarios used in this assessment have been widely examined and presented elsewhere{{< tbib '11' '07aed96a-e0e8-47dd-81d3-cdff5a6e261c' >}},{{
Organizations and volunteers that make up the Northwest’s social safety net are already stretched thin with current demands (very likely, high confidence). Healthcare and social systems will likely be further challenged with the increasing frequency of acute events, or when cascading events occur (very likely, high confidence). In addition to an increased likelihood of hazards and epidemics, disruptions in local economies and food systems are projected to result in more chronic health risks (very likely, medium confidence). The potential health co-benefits of future climate mitigation investments could help to counterbalance these risks (likely, medium confidence).
' uncertainties: 'Preparing and responding to cascading hazards is complex and involves many organizations outside of the medical and public health systems. There is not a common set of metrics or standards for measuring surge capacity and emergency preparedness across the region.
There is uncertainty in whether domestic migration will place further stress on social safety net systems.
' uri: /report/nca4/chapter/northwest/finding/key-message-24-4 url: ~ - chapter_identifier: northwest confidence: 'There is very high confidence that frontline communities are the first to be affected by the impacts of climate change. Due to their enhanced sensitivity to changing conditions, direct reliance on natural resources, place-based limits, and lack of financial and political capital, it is very likely that they will face the biggest climate challenges in the region. However, there is a significant amount of uncertainty in how individuals and individual communities will respond to these changing conditions, and responses will likely differ between states, communities, and even neighborhoods. Thus, it is the complex interaction between the climate exposures and the integrated social-ecological systems as well as the surrounding policy and response environment that will ultimately determine the challenges these communities face.
' evidence: "Multiple lines of research have shown that the impacts of extreme weather events and climate change depend not only on the climate exposures but also on the sensitivity and adaptive capacity of the communities being exposed to those changes.{{< tbib '187' 'b1577125-f789-49e6-9656-c40ed932184a' >}},{{
There are multiple lines of evidence that demonstrate that tribes and Indigenous peoples are particularly vulnerable to climate change. Climate stressors, such as sea level rise, ocean acidification, warmer ocean and stream temperatures, wildfires, or droughts, are projected to disproportionately affect tribal and Indigenous well-being and health,{{< tbib '106' '41bc14ce-5dbf-4eb4-90e2-0689a2bc3565' >}},{{
There is limited research on how climate change is projected to impact farmworkers, yet evidence suggests that occupational health concerns, including heat-related concerns{{< tbib '210' '63fe78ee-2eb9-445b-bbb7-e3f72f3993e0' >}},{{
Particularly relevant to economically disadvantaged urban populations, extensive work has been done evaluating and analyzing social vulnerability{{< tbib '211' '796c4617-7dcd-433e-bb0e-805cdab4c136' >}} and applying that work to the Northwest.{{< tbib '195' 'c6bc7876-ad40-4d51-83e5-49816363385c' >}} There has also been work completed considering both relative social vulnerability and environmental health data (see WSDOH 2018{{< tbib '162' 'f1ca2352-7158-4312-9c4b-3d1189c1ad10' >}}).
Strong evidence through reports and case studies demonstrates that tribes are active in increasing their resilience through climate change vulnerability assessments and adaptation plans (see https://www.indianaffairs.gov/WhoWeAre/BIA/climatechange/Resources/Tribes/index.htm and http://tribalclimateguide.uoregon.edu/adaptation-plans for a list of tribal and Indigenous climate resilience programs, reports, and actions) and through regional networks (for example, Pacific Northwest Tribal Climate Change Network, Affiliated Tribes of Northwest Indians, Northwest Indian Fisheries Commission, Columbia River Inter-Tribal Fish Commission, Point No Point Treaty Council, Upper Snake River Tribes Foundation).
There are also many community organizations across the region focusing on engaging, involving, and empowering frontline communities, including communities of color, immigrants, tribes and Indigenous peoples, and others to design plans and policies that are meaningful (for example, Front and Centered, Got Green, Puget Sound Sage, Coalition of Communities of Color).
" href: https://data.globalchange.gov/report/nca4/chapter/northwest/finding/key-message-24-5.yaml identifier: key-message-24-5 ordinal: 5 process: "This assessment focuses on different aspects of the interaction between humans, the natural environment, and climate change, including reliance on natural resources for livelihoods, the less tangible values of nature, the built environment, health, and frontline communities. Therefore, the author team required a depth and breadth of expertise that went beyond climate change science and included social science, economics, health, tribes and Indigenous people, frontline communities, and climate adaptation, as well as expertise in agriculture, forestry, hydrology, coastal and ocean dynamics, and ecology. Prospective authors were nominated by their respective agencies, universities, organizations, or peers. All prospective authors were interviewed with respect to the qualifications, and selected authors committed to remain part of the team for the duration of chapter development.
The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at workshops, weekly teleconferences, and email exchanges. The author team, along with the U.S. Global Change Research Program (USGCRP), also held stakeholder meetings in Portland and Boise to solicit input and receive feedback on the outline and draft content under consideration. A series of breakout groups during the stakeholder meetings provided invaluable feedback that is directly reflected in how the Key Messages were shaped with respect to Northwest values and the intersection between humans, the natural environment, and climate change. The authors also considered inputs and comments submitted by the public, interested stakeholders, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. For additional information on the overall report process, see Appendix 1: Process. The author team also engaged in targeted consultations during multiple exchanges with contributing authors for other chapters, who provided additional expertise on subsets of the Traceable Accounts associated with each Key Message.
The climate change projections and scenarios used in this assessment have been widely examined and presented elsewhere{{< tbib '11' '07aed96a-e0e8-47dd-81d3-cdff5a6e261c' >}},{{
Communities on the front lines of climate change experience the first, and often the worst, effects. Frontline communities in the Northwest include tribes and Indigenous peoples, those most dependent on natural resources for their livelihoods, and the economically disadvantaged (very high confidence). These communities generally prioritize basic needs, such as shelter, food, and transportation (high confidence); frequently lack economic and political capital; and have fewer resources to prepare for and cope with climate disruptions (very likely, very high confidence). The social and cultural cohesion inherent in many of these communities provides a foundation for building community capacity and increasing resilience (likely, medium confidence).
' uncertainties: "Actual climate change related vulnerabilities will vary by community and neighborhood.{{< tbib '187' 'b1577125-f789-49e6-9656-c40ed932184a' >}},{{
The secondary and tertiary impacts of changing climate conditions are less well understood. For example, climate change may increase the amount and frequency of pesticides used, and the variety of products used to manage crop diseases, pests, and competing weeds.{{< tbib '328' 'c0419502-0517-447b-886f-ece5ec4cda6c' >}} This is likely to increase farmworker exposure to pesticides and ultimately affect their health and well-being. Further, it is unclear how the altered timing of agricultural management of key crops across the United States (for example, the timing of cherry picking) due to increased temperatures and altered growing seasons may influence the demand for farmworker labor, particularly migrant labor, and how this might impact their livelihoods and occupational health.
There is emerging evidence that there are overlaps between environmental justice concerns and climate change impacts on these communities,{{< tbib '233' 'e5aac477-6382-425b-9610-4a288438cd25' >}},{{
No systematic catalogue of the actions and efforts of frontline communities in the region to address their climate-related challenges exists. Thus, at this point, most examples of adaptation and climate preparedness are anecdotal, but these examples suggest an increasing trend to link adaptation efforts that simultaneously address both climate and equity concerns. However, this approach is still used sporadically based on the interests, needs, and resources of the communities.
" uri: /report/nca4/chapter/northwest/finding/key-message-24-5 url: ~ - chapter_identifier: southwest confidence: "The very high confidence in historical droughts derives from the detection and attribution analyses of temperature increases, snow decreases, and soil moisture decreases that have documented hydrologic droughts in California and the Colorado River Basin due to anthropogenic climate change and the conclusions of the Climate Science Special Report (CSSR), Volume I of the Fourth National Climate Assessment.{{< tbib '74' 'a29b612b-8c28-4c93-9c18-19314babce89' >}} The very high confidence in drought projections derives from the multitude of analyses projecting drought in the Southwest under a range of emissions scenarios and the conclusions of the CSSR.{{< tbib '74' 'a29b612b-8c28-4c93-9c18-19314babce89' >}} Only medium confidence is found for flood projections due to lack of consensus in the model projections of precipitation. Increasingly arid conditions and the potential for increased water use by people lead to an assessment of high confidence in the need for new ways to address increasing risks of water scarcity. The actual frequency and duration of water supply disruptions will depend on the preparation of water resource managers with drought and flood plans, the flexibility of water resource managers to implement or change those plans in response to altered circumstances,{{< tbib '481' 'da714e9f-808c-4aae-8d24-aef041988322' >}} the availability of funding to make infrastructure more resilient, and the magnitude and frequency of climate extremes.
" evidence: "Research has found that hotter temperatures can make hydrologic droughts more severe. The unprecedented droughts in the Colorado River Basin and California showed that increased temperatures from climate change intensified the severity of the drought.{{< tbib '13' 'a42c4f5e-f16b-4196-af05-61f117e0491d' >}},{{
The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'Water for people and nature in the Southwest has declined during droughts, due in part to human-caused climate change (very high confidence). Intensifying droughts (very high confidence) and occasional large floods (medium confidence), combined with critical water demands from a growing population, deteriorating infrastructure, and groundwater depletion, suggest the need for flexible water management techniques that address changing risks over time (high confidence), balancing declining supplies with greater demands.
' uncertainties: "Projecting future streamflow and hydrologic characteristics in a basin contains many uncertainties. These differences arise because of uncertainty in temperature and precipitation projections due to differences among global climate models (GCMs), uncertainty in regional downscaling, uncertainty in hydrological modeling, and differences in emissions, aerosols, and other forcing factors. Another important uncertainty is differences in the hemispheric and regional-scale atmospheric circulation patterns produced by different GCMs, which generate different levels of snow loss in different model simulations. A key uncertainty is the wide range in projections of future precipitation across the Southwest;{{< tbib '105' '9d8a98fa-0338-486a-b902-cd02d43cae87' >}} some projections of higher-than-average precipitation in the northern parts of the Southwest could roughly offset declines in warm-season runoff associated with warming.{{< tbib '105' '9d8a98fa-0338-486a-b902-cd02d43cae87' >}}
Detection is the finding of statistically significant changes different from natural cycles. Attribution is the analysis of the relative contribution of different causes and whether greenhouse gas emissions from human sources outweigh other factors. Attribution of extreme events, such as the recent California drought to climate change, is an area of emerging science. On the one hand, Seager et al. (2015){{< tbib '58' '4ca5a43c-5fbe-4cb0-8a7d-7ee3acafd7c0' >}} concluded that the California drought was primarily driven by natural precipitation variability. Sea surface temperature anomalies helped set up the high-pressure ridge over California that blocked moisture from moving inland. On the other hand, Diffenbaugh et al. (2015),{{< tbib '56' '89e08a41-6091-45fa-a92e-6168a90a8151' >}} Williams et al. (2015),{{< tbib '14' 'ba57f86f-c42f-4bba-83f6-676d6875c176' >}} and Berg and Hall (2017){{< tbib '55' '2d7d840f-37b6-4484-ba59-aa2d537a8c7c' >}} concluded that high temperatures from climate change drove record-setting surface soil moisture deficits that made the drought more severe than it would have been without climate change. Storage of increased precipitation in soils may partially offset increased evaporation, possibly making drought less likely.{{< tbib '480' '4fbaaa13-99d2-43df-93db-2be546f18892' >}}
In addition to the uncertainties in regional climate and hydrology projections and attribution studies, other uncertainties include potential changes in water management strategies and responses to accommodate the new changing baseline. Additionally, external uncertainties can impact water use in the region via legal, economic, and institutional options for augmenting existing supplies, adding underground storage and recovery infrastructure, and fostering further water conservation, changes in unresolved water rights, and changes to local, state, tribal, regional and national policies related to the balance of agricultural, ecosystem, and urban water use.
" uri: /report/nca4/chapter/southwest/finding/key-message-25-1 url: ~ - chapter_identifier: southwest confidence: 'Field evidence provides high confidence that human-caused climate change has increased wildfire, tree death, and species range shifts. Projections consistently indicate that continued climate change under higher emissions could increase the future vulnerability of ecosystems, but that reducing emissions and increasing fire management would reduce the vulnerability, providing high confidence in positive benefits of these actions.
' evidence: "Scientific research in the Southwest has provided many cases of detection and attribution of historical climate change impacts. Detection is the finding of statistically significant changes different from natural cycles. Attribution is the analysis of the relative contribution of different causes and whether greenhouse gas emissions from human sources outweigh other factors. Published field research has detected ecological changes in the Southwest and attributed much of the causes of the changes to climate change. Wildfire across the western United States doubled from 1984 to 2015, compared to what would have burned without climate change, based on analyses of eight fuel aridity metrics calculated from observed data, historical observed temperature, and historical modeled temperature from global climate models.{{< tbib '7' 'de4a77df-03ba-4319-a13f-7fdefbb353a5' >}} The increased heat has intensified droughts in the Southwest,{{< tbib '13' 'a42c4f5e-f16b-4196-af05-61f117e0491d' >}},{{
Cutting emissions through energy conservation and renewable energy can reduce ecological vulnerabilities. Under high emissions, projected climate change could triple burned area in the Sierra Nevada, but under low emissions, fire could increase just slightly.{{< tbib '173' '8dfecf8b-f8a8-4f03-8d68-551b13794a1d' >}} Projections of biome shifts{{< tbib '213' '37982de0-0e01-476f-b522-b8162d709134' >}},{{
The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'The integrity of Southwest forests and other ecosystems and their ability to provide natural habitat, clean water, and economic livelihoods have declined as a result of recent droughts and wildfire due in part to human-caused climate change (high confidence). Greenhouse gas emissions reductions, fire management, and other actions can help reduce future vulnerabilities of ecosystems and human well-being (high confidence).
' uncertainties: "Because climate model projections often diverge on whether precipitation may increase or decrease, two broad types of fire futures{{< tbib '152' '391560e0-40c1-4f9d-b063-e87d18c87e02' >}} could be 1) dry-fire future—hotter and drier climate, increased fire frequency, fire limited by vegetation, potential biome change of forest to grassland after a fire due to low natural regeneration, and high carbon emissions; or 2) intense-fire future—hotter and wetter climate, more vegetation, increased fire frequency and intensity, fire limited by climate, and higher carbon emissions. These two broad categories each encompass a range of fire conditions. On the ground, gradients of temperature, precipitation, and climate water deficit (difference between precipitation and actual evapotranspiration) generate gradients of fire regimes. Because climate change, vegetation, and ignitions vary across the landscape, potential fire frequency shows high spatial variability. Therefore, future fire types could appear in patches across the landscape, with different fire future types manifesting themselves in adjacent forest patches. Changes in aridity may shift some plant and animal species ranges downslope to favorable combinations of available moisture and suitable temperature, rather than upslope.{{< tbib '484' '9743c446-fef0-44f4-82bd-7f2ff1614205' >}} Plants and animals may respond to changing climate, and have been shown to do so, through range shifts, phenology shifts, biological evolution, or local extirpation. Thus, no single expected response pattern exists.{{< tbib '224' '820ced23-71ae-4607-8353-74e3881db2a1' >}}
" uri: /report/nca4/chapter/southwest/finding/key-message-25-2 url: ~ - chapter_identifier: southwest confidence: 'Field measurements at numerous locations have detected sea level rise, ocean warming, ocean acidification, and ocean hypoxia. Multiple model-based analyses have attributed these changes to human-caused climate change, giving high confidence to these impacts of climate change.
' evidence: "At the Golden Gate Bridge, San Francisco, sea level rose 9 ± 0.4 inches (22 ± 1 cm) from 1854 to 2016,{{< tbib '236' '8e1ab38d-5d31-4a6a-8ad6-e06fe74a4aa1' >}} and at San Diego, 9 ± 0.8 inches (24 ± 2 cm) from 1906 to 2016.{{< tbib '237' '1f19738a-f4ec-4a51-8478-b88163d6dea6' >}} Analyses of these gauges and hundreds around the world show a statistically significant increase in global mean sea level{{< tbib '238' '94a8514e-063e-45ef-b893-11c82b49a597' >}},{{
The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'Many coastal resources in the Southwest have been affected by sea level rise, ocean warming, and reduced ocean oxygen—all impacts of human-caused climate change (high confidence)—and ocean acidification resulting from human emissions of carbon dioxide (high confidence). Homes and other coastal infrastructure, marine flora and fauna, and people who depend on coastal resources face increased risks under continued climate change (high confidence).
' uncertainties: "Catastrophic rapid loss of Antarctic and Greenland ice sheets could increase sea level more rapidly. Sea level rise at individual locations depends on the form of the seafloor (bathymetry) and other local conditions. Climate change impacts compound overfishing and make fish populations more vulnerable. Potential economic changes in California’s coastal and marine-based economies are subject to many different environmental and socioeconomic factors.
The full complexity of ecological responses to ocean acidification in combination with other stresses in California marine waters is currently unknown. Food supply for marine species,{{< tbib '487' 'cf677518-2ff0-4462-8d41-e48e8655ba18' >}} natural variation in resilience,{{< tbib '488' '04a02114-e2b5-4c87-8c34-5658bc4f3c05' >}},{{
The documented human-caused increase in temperature is a key driver of regional impacts to snow, soil moisture, forests, and wildfire, which affect Indigenous peoples, other frontline communities, and all of civil society. Case study evidence, using Indigenous and Western scientific observations, oral histories, traditional knowledge and wisdom (e.g., Ferguson et al. 2016{{< tbib '493' 'd630a483-2475-4fbb-b942-e5068ac04971' >}}), suggests that climate change is affecting the health, livelihoods, natural and cultural resources, practices, and spiritual well-being of Indigenous communities and peoples in the Southwest (e.g., Redsteer et al. 2011, 2013; Wotkyns 2011; Cozzetto et al. 2013; Gautam et al. 2013; Navajo Nation Department of Fish and Wildlife 2013; Nania and Cozzetto et al. 2014; Sloan and Hostler 2014; Redsteer and Fordham 2017{{< tbib '44' '85923ac2-22e6-4265-9d70-1887132abfce' >}},{{
Abundant evidence and strong agreement among sources exist regarding current impacts of climate change in the region. Impacts of climate change on the food sources, natural resources-based livelihoods, cultural resources and practices, and spiritual health and well-being of Southwest Indigenous peoples are supported, in part, by evidence of regional temperature increases,{{< tbib '23' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}},{{
Impacts specific to Indigenous peoples include: 1) declining surface soil moisture, higher temperatures, and evaporation converge with oak trees’ decreased resilience,{{< tbib '285' 'd04b2c86-5ca0-42e0-9792-2f319c15cd7e' >}} diminished acorn production, and fire and pest threat to reduce the availability and quality of acorns for tribal food consumption and cultural purposes;{{< tbib '306' 'debdf209-4050-4706-965c-09cff7ec353b' >}} and 2) declining vegetation, higher temperatures, diminished snow, and soil desiccation have caused dust storms and more mobile dunes on some Navajo and Hopi lands, resulting in damaged infrastructure and grazing lands and loss of valued native plant habitat.{{< tbib '44' '85923ac2-22e6-4265-9d70-1887132abfce' >}},{{
Multiple projections of climate and hydrological changes show potential future change and disruption to the ecosystems on which Indigenous peoples depend for their natural resources-based livelihoods, health, cultural practices, and traditions. These include projections of increased temperatures and heat extremes;{{< tbib '24' 'acbb7b12-c119-4c42-8a80-c2555964db4c' >}} longer, more severe, and more frequent drought;{{< tbib '13' 'a42c4f5e-f16b-4196-af05-61f117e0491d' >}},{{
Evidence of specific future disruptions to traditional food sources from forests and oceans mostly relies upon inferences, based on projections of changing seasonality and associated phenological or ecosystem responses{{< tbib '298' '6848eec2-534b-4629-967c-53d8530089a3' >}},{{
Abundant evidence exists of autonomous adaptation strategies, projects, and actions, rooted in traditional environmental knowledge and practices or integration of diverse knowledge systems to inform ecological management to support adaptation and ecosystem resilience.{{< tbib '490' '953476ae-1357-48a5-99d8-1daf963f0a3c' >}},{{
In response to the current and future projected climate changes and ecosystem disruptions, a number of tribes in the Southwest are planning and implementing energy efficient and renewable energy projects.{{< tbib '327' 'fda7d18b-acc5-46fc-9863-3b4ac6a609be' >}},{{
Several tribes in the Southwest are developing climate change adaptation plans to address the current climate-related impacts and prepare for future projected climate changes. The Santa Ynez Band of Chumash Indians, which is working towards an integrated energy and climate action plan, the Yurok Tribe, the Gila River Indian Community, and the Tohono O’odham Nation are among the first tribes in the region to develop climate adaptation and resilience plans, which reflects a nationwide gap or need for further tribal adaptation plan development. Lack of capacity and funds has hindered progress in moving from planning to implementation, which is similar to the situation for U.S. cities.{{< tbib '497' '8a61b1a7-bb52-496d-86f7-21911efcf5f8' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/southwest/finding/key-message-25-4.yaml identifier: key-message-25-4 ordinal: 4 process: 'The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'Traditional foods, natural resource-based livelihoods, cultural resources, and spiritual well-being of Indigenous peoples in the Southwest are increasingly affected by drought, wildfire, and changing ocean conditions (very likely, high confidence). Because future changes would further disrupt the ecosystems on which Indigenous peoples depend (likely, high confidence), tribes are implementing adaptation measures and emissions reduction actions (very likely, very high confidence).
' uncertainties: "Uncertainties in the climate and hydrologic drivers of regional changes affecting Indigenous peoples in the Southwest include 1) differences in projections from multiple GCMs and associated uncertainties related to regional downscaling methods, 2) the way snow is treated in regional modeling,{{< tbib '498' '64014404-d26e-45c7-9b33-8e2253a9ca04' >}} 3) variability in projections of extreme precipitation, and, in particular, 4) uncertainties in summer and fall precipitation projections for the region.{{< tbib '88' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} Additional uncertainties exist in sea level rise projections{{< tbib '242' 'a1aee4ba-d4fc-4f92-a74a-e37189c138b5' >}} and, for the California coast, ocean process model projections of acidification, deoxygenation, and warming coastal zone temperatures.{{< tbib '499' '99e25417-f6c0-49f1-87cd-e9af689f3cff' >}} For the most part, Native lands lack instrumental monitoring for weather and climate, which is a barrier for long-term climate-related planning.{{< tbib '493' 'd630a483-2475-4fbb-b942-e5068ac04971' >}}
Complexities arising from the multiple factors affecting ecosystem processes, including tree mortality and fire, often preclude formal detection and attribution studies. Much evidence and agreement among evidence exist regarding the role of hotter temperatures in fire and tree mortality.{{< tbib '7' 'de4a77df-03ba-4319-a13f-7fdefbb353a5' >}},{{
Other uncertainties relate to estimating future vulnerabilities and impacts, which depend, in part, on adjudication of unresolved water rights and the potential development of local, state, regional, tribal, and national policies that may promote or inhibit the development and deployment of adaptation and mitigation strategies.
" uri: /report/nca4/chapter/southwest/finding/key-message-25-4 url: ~ - chapter_identifier: southwest confidence: "Hydrological drought in California reduced hydroelectric generation{{< tbib '335' '8347d2b2-855d-4765-b7a2-6d2a9e0c99f4' >}} and fossil fuel electricity generation efficiencies. Drought and rising temperatures under climate change can reduce the ability of hydropower and fossil fuel electricity generation to meet growing energy use in the Southwest (very likely, very high confidence). Renewable solar and wind energy offers increased electricity reliability, lower water intensity for energy generation, reduced greenhouse gas emissions, and new economic opportunities (likely, high confidence).
" evidence: "Numerous studies link Southwest hydrologic drought with a decline in renewable hydroelectricity generation in the region. Hydroelectric generation depends on runoff to fill reservoirs to maximize generation capacity.{{< tbib '336' '7db8f4ff-81fb-4d22-949a-076aab55aa86' >}},{{
Similarly, low reservoir levels in Lake Mead—which is formed by damming the Colorado River—driven by reduced Colorado River runoff{{< tbib '13' 'a42c4f5e-f16b-4196-af05-61f117e0491d' >}},{{
Fossil fuel generation efficiency depends on the temperature and availability of the external cooling water. Warming could reduce energy efficiency up to 15% across the Southwest by 2100.{{< tbib '91' '8c12cc4c-3448-4055-b7a2-e03ead1c2572' >}} Higher temperatures also increase electric resistance in transmission lines, causing transmission losses of 7% under higher emissions.{{< tbib '344' '673a11a4-4d3c-4303-af82-29de1ca24bd6' >}} Replacing fossil fuel generation with solar power renewables reduces greenhouse gas emissions and water use per unit of electricity generated.{{< tbib '90' '437ba8f2-66cf-44f5-8bea-173c02458858' >}} This supports the assertion that increasing solar energy generation in the Southwest could meet the energy demand no longer being met by hydropower and fossil fuel as well as the expected increase in energy use in the future.
Solar energy production is also an economic opportunity for the region. The energy potential for renewable energy is estimated to range from one-third to over ten times 2013 generation levels from all sources.{{< tbib '502' '2c0c6750-e017-4590-b7aa-e1756bc7854b' >}} The lower range assumes capacity requirements remain at 2013 levels,{{< tbib '502' '2c0c6750-e017-4590-b7aa-e1756bc7854b' >}} but recent data show an upward trend in Southwest energy use.{{< tbib '89' 'ab3cc54d-c74f-4a6d-8746-efa051c2e97e' >}}
The high potential for solar energy projects in the Southwest and the extent of federally owned land in the Southwest (well over half the total surface area for the six-state region) prompted the Bureau of Land Management (BLM) and the U.S. Department of Energy to conduct a programmatic environmental impact analysis of a new Solar Energy Program to further support utility-scale solar energy development on BLM-administered lands.{{< tbib '502' '2c0c6750-e017-4590-b7aa-e1756bc7854b' >}},{{
Solar and renewable energy jobs are increasing. The solar workforce increased 25% in 2016, while wind employment increased 32%.{{< tbib '505' '92b75533-4ebe-4cad-af48-6789b4627f47' >}} Jobs in low-carbon-emission generation systems, including renewables, nuclear, and advanced low-emission natural gas, comprise 45% of all the jobs in the electric power generation and fuels technologies.{{< tbib '505' '92b75533-4ebe-4cad-af48-6789b4627f47' >}} Growing Southwest energy use, competitive prices for renewables, and the renewable energy potential of the Southwest favor the replacement of fossil-fuel-generated energy by renewable solar and wind energy.
" href: https://data.globalchange.gov/report/nca4/chapter/southwest/finding/key-message-25-5.yaml identifier: key-message-25-5 ordinal: 5 process: 'The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'The ability of hydropower and fossil fuel electricity generation to meet growing energy use in the Southwest is decreasing as a result of drought and rising temperatures (very likely, very high confidence). Many renewable energy sources offer increased electricity reliability, lower water intensity of energy generation, reduced greenhouse gas emissions, and new economic opportunities (likely, high confidence).
' uncertainties: "Climate model projections of the future diverge on whether precipitation may increase or decrease for much of the region, so hydroelectric power changes may exhibit spatial variation. The amount of runoff is a key factor driving the generation potential for hydroelectric power. A key uncertainty is how much hydroelectricity generation will decline. Some projections of higher-than-average precipitation in the northern parts of the Southwest could roughly offset declines in warm-season runoff associated with warming.{{< tbib '105' '9d8a98fa-0338-486a-b902-cd02d43cae87' >}}
Energy demand in the Southwest is increasing, but the rate of growth is uncertain.{{< tbib '506' '561029d5-4494-43bf-98d2-96ad38606588' >}} Changes in energy market prices cause future uncertainty in the future mix of energy sources for the Southwest.{{< tbib '502' '2c0c6750-e017-4590-b7aa-e1756bc7854b' >}} The low cost of natural gas and the competitive cost of solar and wind renewables make it somewhat certain the proportion of the energy generated from these sources will continue to increase and offset reductions in traditional fossil-fuel-generated energy, reducing overall greenhouse gas emissions.{{< tbib '504' '1f8c0eab-9564-4064-bd8e-b98c135744e9' >}} Renewable energy job growth potential is also uncertain and depends on the factors mentioned above.{{< tbib '505' '92b75533-4ebe-4cad-af48-6789b4627f47' >}}
Additionally, daily to multiyear variation in coastal cloud cover affects solar electricity generation potential along the California coast.{{< tbib '507' 'beba4436-bbd0-43c2-bd04-e6000c5e4a27' >}},{{
Since the availability of affordable food around the world depends upon complex trade and transportation networks, the effects of climate change on Southwest food availability, production, and affordability remain highly complex and thereby uncertain and classified with medium confidence. While the viability of rural livelihoods is vulnerable to water shortages and other climate-related risks, rural livelihoods may be supplemented by other nonagricultural income, such as recreation and hunting. The viability of rural livelihoods is highly complex, and risk is, therefore, classified with medium confidence. Crop impacts related to hotter and drier conditions and reduced winter chill periods, caused by climate change, are classified with medium confidence. Not all crops are directly harmed by warming temperatures, and the simulation impacts of reduced chilling hours can produce a fairly wide range of results depending upon model assumptions. Hotter and drier conditions can directly harm livestock via reduced forage quantity and quality and exposure to higher temperatures, conferring a high confidence classification. Projections of future drought and water scarcity portend increased competition for water from other beneficial uses with medium confidence.
' evidence: "Climate change has altered climate factors fundamental to food production and rural livelihoods in the Southwest. Abundant evidence and good agreement in evidence exist regarding regionally increasing temperatures, reduced soil moisture, and effects on regional snowpack and surface water sources.{{< tbib '13' 'a42c4f5e-f16b-4196-af05-61f117e0491d' >}},{{
Elevated temperatures can be associated with failure of some crops, such as warm-season vegetable crops, and reduced yields and/or quality in others.{{< tbib '374' 'c29be9d3-c558-41ec-979c-f8d0c0b6f0e6' >}} Temperatures in California, Nevada, and Arizona are already at the upper threshold for corn{{< tbib '372' '53efddbf-8a1f-44fb-83e2-167fde08c9aa' >}} and rice.{{< tbib '373' 'a7cfed2a-25b6-4d4f-a9dc-49e1568e2aea' >}} While crops grown in some areas might not be viable under hotter conditions, other crops such as olives, cotton, kiwi, and oranges may replace them.{{< tbib '375' '0a8508df-df59-4080-89a2-52bfeaca47e0' >}} In the Southwest, climate change may cause a northward shift in crop production, potentially displacing existing growers and affecting rural communities.{{< tbib '376' '4442506b-fbba-41ea-9cef-1eac88ce2049' >}} Quality of specialty crops, both nutritive and sensory, declines because of increased temperatures and other changes associated with a changing climate,{{< tbib '393' '3baf471f-751f-4d68-9227-4197fdbb6e5d' >}},{{
High ambient temperatures associated with climate change could decrease production of rangeland vegetation across the Southwest,{{< tbib '384' 'aa6f4075-c70e-43f8-969e-b5625ad25449' >}} reducing available forage for livestock. Ranching enterprises across the region have vastly different characteristics that will influence their adaptive capacities.{{< tbib '390' 'c779538d-b066-4e38-8527-ff3f7552f26e' >}}
Local-scale impacts can vary considerably across the region depending upon surface and groundwater availability. Drought causes altered water management, with heavy reliance on a limited groundwater to sustain regional food production.{{< tbib '130' '7aecf6b3-0b12-40d7-8c61-c1b72cc14289' >}} Despite severe localized impacts, losses in total agricultural revenue are buffered by groundwater reliance to offset surface water shortage.{{< tbib '369' '53ceb8c3-f1b8-4cc1-bb65-3268f4f8bb74' >}} Parts of the Southwest have exhausted sustainable use of groundwater resources. When surface water supplies are reduced, farmers shift to increased groundwater pumping, even when pumping raises production costs{{< tbib '371' 'cf96b502-57a2-4b76-bffc-750e1bf668d6' >}}—declining groundwater tables significantly increase pumping costs and require drilling of deeper wells.{{< tbib '130' '7aecf6b3-0b12-40d7-8c61-c1b72cc14289' >}} Continued climate change may reduce aquifer recharge in the southern part of the region 10%–20%.{{< tbib '370' '2042ab8a-6a82-40a2-99ba-7e67babf8ffc' >}} Climate change is projected to cause longer and more severe drought periods that will intensify the uncertainty associated with Southwest water supply and demand. Water-intensive forage crops and the livestock industry are especially vulnerable to climate-related water shortages.{{< tbib '15' 'bf7e284b-6333-477d-883f-23e002742a6c' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/southwest/finding/key-message-25-6.yaml identifier: key-message-25-6 ordinal: 6 process: 'The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'Food production in the Southwest is vulnerable to water shortages (medium confidence). Increased drought, heat waves, and reduction of winter chill hours can harm crops (medium confidence) and livestock (high confidence); exacerbate competition for water among agriculture, energy generation, and municipal uses (medium confidence); and increase future food insecurity (medium confidence).
' uncertainties: "The impacts of climate change on food production depend upon microclimatology and local-scale environmental, social, and economic resources. While the scientific community relies upon computer models and generalized information to project likely future conditions, unforeseen consequences of warming temperatures, such as those related to pests, pollinators, and pathogens, may be more detrimental than some of the well-documented projections, such as temperature impacts on reduced yields. The effects of increased precipitation supplying the deep root zone may somewhat offset the increase in temperature, so agricultural drought may be less frequent for trees and other crops dependent on deeper soil moisture.{{< tbib '480' '4fbaaa13-99d2-43df-93db-2be546f18892' >}} Scientists are producing more drought- and heat-tolerant cultivars, which may be suitable to production in the projected warmer and more arid climate of the Southwest.
Since food security relies on complex national and international trade networks, how regional climate change may affect local food security is uncertain. Many adaptation options, such as using alternate breeds, crops, planting and harvest dates, and new (sometimes untested) chemicals, may work in certain situations but not others. Thus, predicting impacts to food production in a hotter/drier land is likely to vary by crop and location, necessitating flexibility and adaptive management. Of paramount uncertainty is the impact of water shortage on regional food production as other uses may outcompete producers for limited supplies.
" uri: /report/nca4/chapter/southwest/finding/key-message-25-6 url: ~ - chapter_identifier: southwest confidence: "Evaluation of confidence levels for the assessment of the type and magnitude of observed or projected public health and clinical impacts was based on the strength of evidence underlying the answers to three primary questions:
What characteristics of the region’s historical climate and weather patterns translate directly (for example, extreme heat) or indirectly (for example, higher temperatures fostering ozone formation or the growth and spread of pathogens and vectors) to exposures associated with observed human health risks that are unique to or overrepresented in the Southwest?
Does recent historical evidence indicate that climate and weather patterns have changed, or do climate models project changes over the 21st century, thereby increasing the risk of human exposures and health impacts evaluated under question 1?
What are the determinants of individual and population vulnerability that increase or decrease the risk of an adverse health outcome or affect adaptive capacity? These include factors that affect a) biological susceptibility, b) physical environment and exposure characteristics, and c) social, behavioral, or economic factors.
To the extent possible, the evaluation recognized and accounted for the complex interconnections among these factors, the fact that their relative importance may differ across geographic and temporal scales, and the combined uncertainties of evidence from multiple disciplines (for example, health sciences, climatology, and social or behavioral sciences) that can vary substantially.
The information revealed by answering those questions, gives high confidence that extreme heat will be the dominant driver of exposures that pose the greatest health risks in the Southwest—including direct effects of heat on individuals and indirect effects of heat on air pollution levels. Due to the uncertainties related to the frequency and intensity of human exposures and related to impacts on essential ecosystem services under projected climate change, the statement “Improving public health systems, community infrastructure, and personal health can reduce serious health risks under future climate change” is made with medium confidence. Nevertheless, clinical and public health policy effectiveness assessments show that such improvements can reduce the burden of disease and health risks associated with environmental exposures.
" evidence: "Strong evidence and good agreement among multiple sources and lines of evidence exist, indicating that the Southwest regional temperature may increase, snowpack may decline, soil moisture may decrease, and drought may be prolonged.{{< tbib '14' 'ba57f86f-c42f-4bba-83f6-676d6875c176' >}},{{
Exposure to hotter temperatures and extreme heat events, partly a manifestation of human-caused climate change, already led to heat-associated deaths and illnesses in heat waves in Arizona and California in the early and mid-2000s.{{< tbib '398' 'b3e00a14-a876-44fa-9c1f-836bd53a7f69' >}},{{
Good agreement exists among models that most of the Southwest may become more arid, due to the effect of increasing temperatures on snow, evaporation, and soil moisture.{{< tbib '58' '4ca5a43c-5fbe-4cb0-8a7d-7ee3acafd7c0' >}},{{
Strong evidence exists of the effects of extreme heat on public health in the region (e.g., Knowlton et al. 2009, Oleson et al. 2015, Wilhelmi et al. 2004{{< tbib '400' '7ca0e947-163a-46f3-9274-cea209b94510' >}},{{
Given the proportion of the U.S. population in the Southwest, a disproportionate number of West Nile virus, plague, hantavirus pulmonary syndrome, and Valley fever cases occur in the region.{{< tbib '158' 'd8bd2def-be9b-47e3-84de-199bcd26c31d' >}},{{
Overall, the Southwest is ill-prepared to absorb the additional patient load that would accompany climate change associated disasters.{{< tbib '448' 'e523f9c0-56f9-44ff-b2d9-7debec2a19d0' >}} The American College of Emergency Physicians assigned an overall emergency care grade of C or C+ to three of the six Southwest states, with the others receiving poorer grades, and four of the six states received an F grade for access to emergency care.{{< tbib '448' 'e523f9c0-56f9-44ff-b2d9-7debec2a19d0' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/southwest/finding/key-message-25-7.yaml identifier: key-message-25-7 ordinal: 7 process: 'The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
' report_identifier: nca4 statement: 'Heat-associated deaths and illnesses, vulnerabilities to chronic disease, and other health risks to people in the Southwest result from increases in extreme heat, poor air quality, and conditions that foster pathogen growth and spread (high confidence). Improving public health systems, community infrastructure, and personal health can reduce serious health risks under future climate change (medium confidence).
' uncertainties: "Uncertainties in the climate and hydrologic drivers of regional changes affecting public health include 1) differences in projections from multiple GCMs and associated uncertainties related to regional downscaling methods, 2) variability in projections of extreme precipitation, 3) uncertainties in summer and fall precipitation projections for the region,{{< tbib '88' 'e8089a19-413e-4bc5-8c4a-7610399e268c' >}} and 4) uncertainties in models that project occurrence and levels of climate-sensitive exposures that are known to impact public health, such as local and regional ozone air pollution, particulate air pollution (for example, increases from wildfire emissions or reductions from advancements in vehicle emissions control technology), or occurrence and exposure to toxins or pathogens.
Studies of non-fatal illnesses using healthcare services data can yield critical insights different from those one can derive from death data. Most studies of heat impacts on health have focused on deaths rather than nonfatal illnesses. This is primarily because hospitalization and emergency department data, compared with death certificate data, are not as available or uniform across locations, and when they are available it can be difficult to access them due to concerns for patient confidentiality. Ongoing enhancements to electronic medical records technology and adoption across the healthcare services sector will potentially address those limitations in the near future and will provide invaluable data resources to identify and adopt prevention strategies that reduce the vulnerability of patients and populations to the adverse effects of climate-sensitive exposures.
More recent work focusing on the more deadly neuroinvasive West Nile virus indicates that regionally, the central and southern parts of the country may experience increasing cost from this vector-borne disease in the future.{{< tbib '178' '0b30f1ab-e4c4-4837-aa8b-0e19faccdb94' >}},{{
While improvements to individual health and to clinical and community infrastructure are highly likely to 1) improve physical capacity to adapt to climate effects, 2) diminish the overall impacts on population health, and 3) increase societal capacity to respond quickly to dampen the effects of long-term and emergency responses,{{< tbib '446' '46b92d0e-f9f2-4b12-8b9e-8c27d6a4b9da' >}},{{
There is very high confidence that the arctic sea ice will continue to reduce in size over the next 20–40 years, and it is likely that the Arctic Ocean will be nearly ice-free in late summer by mid-century based on current climate models. There is also high confidence that this melting will have an effect on the northward expansion of North Pacific fish species and associated effects on associated food webs. There is very high confidence that continued melting of the Arctic Ocean ice will have an effect on the habitat and behavior of polar bear and walrus. There is high confidence that Alaska’s ocean waters are becoming increasingly acidic. Given this increase, it is very likely that there will be biological impacts, but it is uncertain which species will be affected and to what extent.
' evidence: "Changes in arctic sea ice and its impacts on marine ecosystems and various biological resources are well documented by 38 years of satellite records{{< tbib '280' '2aa47611-1a24-4796-b0a8-a0ba3092e470' >}} and the scientific literature.{{< tbib '48' '13e01b3b-caf8-4d85-ac0f-5689df47762a' >}},{{
The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.
' report_identifier: nca4 statement: 'Alaska’s marine fish and wildlife habitats, species distributions, and food webs, all of which are important to Alaska’s residents, are increasingly affected by retreating and thinning arctic summer sea ice, increasing temperatures, and ocean acidification. Continued warming will accelerate related ecosystem alterations in ways that are difficult to predict, making adaptation more challenging (very likely, very high confidence).
' uncertainties: 'To date, relatively few of Alaska’s marine species have been studied for their response to ocean acidification, and the assessment of potential impacts is challenging due to each species’ differing habitats, life cycle stages, and response and adaptation mechanisms. It is known that some organisms respond more dramatically to environmental change than others, and warming ocean temperatures may be more significant in the short term than ocean acidification. There is significant uncertainty in the projected increase of shipping through the Arctic and the Bering Strait, since much of this increase will be driven by economic factors and not climate or other environmental change.
' uri: /report/nca4/chapter/alaska/finding/key-message-26-1 url: ~ - chapter_identifier: alaska confidence: 'There is high confidence that wildfire in Alaska will continue but medium confidence as to its ultimate effect on vegetation and permafrost, which is often dependent on fire fields available (e.g., older forests or new growth shrublands), the fire intensity, and the return rate. There is high confidence that the north coast of Alaska is eroding at high rates. It is likely that coastal erosion is accelerating in response to climate change but medium to low confidence as to the location and rate because of limited studies and datasets documenting this. There is high confidence that river erosion will continue but medium confidence as to when, where, and to what extent this will occur across Alaska because of differences in local climatic and geographic qualities of the area in question. There is high confidence and it is likely that the glaciers in Alaska will continue to diminish, especially those that are tidewater glaciers.
' evidence: "Permafrost
Multiple studies of permafrost in Alaska have shown that the gradual warming of the ground{{< tbib '105' '5a612de8-a07d-48c0-a7ca-c4b705157070' >}} has resulted in the warming and thawing of permafrost over the past 30 years,{{< tbib '79' '7fbfdebd-eb73-40be-88ec-109ad7a226fd' >}},{{
Wildfire
It has been well documented that wildfires are a common occurrence in Alaska, especially the interior boreal areas, although they have also occurred in areas of arctic tundra,{{< tbib '114' '9e7065c6-93b9-4bf7-8883-3547a9199ea6' >}},{{
Coastal and River Erosion
The shoreline along Alaska's northern coast has eroded at some of the fastest rates in the Nation, putting local communities, oil fields, and coastal habitat at risk.{{< tbib '19' 'cf15559b-f1e8-4022-945b-45ab149dc1a8' >}} Unlike the contiguous United States, Alaska is subject to glacial and periglacial processes that make permafrost and sea ice key controlling factors of coastal erosion and flooding. Thermal degradation of permafrost leads to enhanced rates of erosion along permafrost-rich coastal shorelines{{< tbib '19' 'cf15559b-f1e8-4022-945b-45ab149dc1a8' >}} and subsidence of already low-lying regions. Longer sea ice-free seasons, higher ground temperatures, and relative sea level rise are expected to exacerbate flooding and accelerate erosion in many regions, leading to the loss of more shoreline in the future.{{< tbib '19' 'cf15559b-f1e8-4022-945b-45ab149dc1a8' >}}
While erosion and changed river courses are a normal part of landscape evolution, lateral river erosion rates are likely to change over time, but the direction and magnitude of these changes are poorly understood. Major river erosion events are typically tied to high hydrological flows or the melting of permafrost along river and stream banks. Statewide, evidence for changes in maximum gauged streamflows is mixed, with a majority of locations having no significant trend.{{< tbib '289' '41ed988f-4fa6-476d-90c9-ef9e3e8d1806' >}} There is significance for seasonal changes in the timing of peak flows in interior Alaska, though increases in the absolute magnitude are not well evident in existing data.{{< tbib '290' '5e61fa98-c1ff-42e6-aa82-10dad90342d9' >}} Riverine erosion is a serious problem for a significant number of communities.{{< tbib '123' '49a37e8f-eef6-4ee6-9705-fac54c48df30' >}} Significant resources have been expended to slow erosion at some communities, often through the construction of berms and bank stabilization projects. These projects have a mixed record of success and nearly always require ongoing maintenance.
Glacier Change
Airborne altimetry surveys of Alaska glaciers spanning the 1994–2013 interval and covering about 40% of the region’s glacierized area{{< tbib '137' 'df531aa2-4a99-4ce7-9dd9-744729e2161d' >}} yield decadal timescale mass balance estimates for individual glaciers and a regional estimate.{{< tbib '291' '08047702-47b0-4401-ab44-a0f46a16efe5' >}} Several new modeling studies suggest that the measured rates of Alaska ice loss are likely to increase in coming decades,{{< tbib '139' 'c426adb7-b055-4726-80f1-82d7846f46c0' >}},{{
Interdisciplinary research along the Gulf of Alaska is providing new insights into the role of glacier runoff in structuring downstream freshwater and nearshore marine ecosystems.{{< tbib '101' '141ed68e-5810-4735-afee-878ceb6041cc' >}} End-of-century projections from physically based models suggest that anticipated atmospheric warming (2°–4.5°C) will drive volume losses of 32%–58% for Alaska glaciers.{{< tbib '142' '226e7316-1460-4cfe-94a1-4bca27549241' >}} Increases in river chemical ions due to glacial runoff and permafrost melt have also been associated with diminishing glaciers in Alaska.{{< tbib '94' '7c14626a-343f-48a3-9076-1bd656f663c3' >}},{{
The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.
' report_identifier: nca4 statement: 'Alaska residents, communities, and their infrastructure continue to be affected by permafrost thaw, coastal and river erosion, increasing wildfire, and glacier melt. These changes are expected to continue into the future with increasing temperatures, which would directly impact how and where many Alaskans will live (very likely, high confidence).
' uncertainties: 'Some events such as wildfires and coastal storms are dependent on regional and local current weather conditions, and the exact landscape or ecosystem response can be highly variable. Future effects are also dependent on quick response actions and adaptation measures.
' uri: /report/nca4/chapter/alaska/finding/key-message-26-2 url: ~ - chapter_identifier: alaska confidence: 'There is high confidence that there will be a continuation of trends causing higher winter temperatures, increased storm events, increased frequency and extent of wildfires, and increased permafrost thawing with associated erosion. Given these trends, there is very likely to be subsequent human health effects, but the distribution and magnitude of these effects remain uncertain.
' evidence: "The evidence base for climate-related health threats can be divided into three main categories. First are those threats that have strong documentation of both the climate or environmental driver and the health effect. An example is the emergence of gastrointestinal illness due to the northward expansion of the bacteria Vibrio parahaemolyticus among Alaska shellfish. Other threats with a similar level of evidence include increased venomous insect stings.
Second, some health threats are based on a combination of well-documented climate-driven environmental changes and records of anecdotal community observations of health impacts. Examples include the increased risk of injury or death from exposure among winter subsistence-related travelers or respiratory problems from smoke inhalation during wildfires. The community observations of these threats point to a real trend.{{< tbib '10' 'cc3776b7-7ea8-42e9-802d-2ef5e6ac2f40' >}},{{
The third category is those threats that are logical inferences of potential health risks based on documented environmental changes and community-vulnerability assessments. Examples include the well-documented threats from coastal storms to community infrastructure and shorelines and the damage to community water and sanitation systems from permafrost thawing or erosion. The risk of physical harm from major storm or flooding events is obvious, and the loss of a water/sewer system would likewise pose a clear threat to health through waterborne or water-washed infections. However, these threats are based on likely outcomes from existing trends in environmental change. The human health effects are either undocumented or are anticipated in the future. Many of the infectious disease risks and harmful algal blooms (HABs) fall into this category; where range expansion of pathogens or vectors is occurring, health effects are likely to follow.
" href: https://data.globalchange.gov/report/nca4/chapter/alaska/finding/key-message-26-3.yaml identifier: key-message-26-3 ordinal: 3 process: 'The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.
' report_identifier: nca4 statement: 'A warming climate brings a wide range of human health threats to Alaskans, including increased injuries, smoke inhalation, damage to vital water and sanitation systems, decreased food and water security, and new infectious diseases (very likely, high confidence). The threats are greatest for rural residents, especially those who face increased risk of storm damage and flooding, loss of vital food sources, disrupted traditional practices, or relocation. Implementing adaptation strategies would reduce the physical, social, and psychological harm likely to occur under a warming climate (very likely, high confidence).
' uncertainties: 'The greatest uncertainties in the health threats of climate change lie in the geographic distribution, magnitude, duration, and capacity to detect the effects. Many of the impacts of climate changes are most evident in rural Alaska, which is an enormous area and sparsely populated. Thus, sporadic events with geographic variability such as storms or HABs may have a range of human health effects from none to severe, depending on the timing and location of exposure. Likewise, the magnitude and duration of the effects on health are difficult to predict based on variability in the source of risk and human adaptation. The lack of repeated outbreaks of V. parahaemolyticus illnesses from raw shellfish consumption is a good example of how adaptations in aquaculture practices and commercial regulations, along with likely changes in consumer practices, appear to have reduced the magnitude of the health threats, compared with initial outbreak. Finally, we have limited capacity to detect many of the health outcomes associated with climate change. The organized reporting and monitoring of climate-linked health effects by public health are limited to the toxin-mediated illnesses, some of the infectious diseases, mortality events, and unusual clusters of illnesses or injuries. Even among those conditions, underreporting of illnesses is common due to healthcare-seeking behavior, lack of recognition by medical providers due to unfamiliarity or limited diagnostic capacities, or incomplete compliance. For many of the anticipated health effects, such as nonoccupational injuries, mental health issues, and respiratory conditions, there may be documentation in a person’s individual health records, but no systems are in place to collect such information and link these illnesses to climate or environmental events or conditions. Large administrative healthcare databases, such as the Alaska Hospital Discharge Data System or the Alaska Health Information Exchange, could be used for focused investigations or ongoing monitoring. However, these would only be useful for severe illnesses with large geographic or multiyear distributions. These datasets would likely miss health events that do not result in emergency room visits or hospitalizations, that are rare, or that occur in irregular episodes. Data from ambulatory clinic visits, community surveys, or syndrome-based surveillance efforts would be needed to detect and characterize uncommon or less severe health occurrences.
' uri: /report/nca4/chapter/alaska/finding/key-message-26-3 url: ~ - chapter_identifier: alaska confidence: 'There is high confidence that climate change is having far-reaching effects on Alaska’s Indigenous peoples. It is likely that most of these impacts will have negative effects, as they undermine existing behaviors, patterns, infrastructure, and expectations. It is also likely that there will continue to be some benefits and opportunities stemming from climate-related changes. There is medium confidence that the negative impacts can be reduced and the new opportunities maximized with appropriate policy and regulatory action, as not all aspects of change can be addressed in this way, and it is unclear whether such a systematic approach is plausible in light of the way programs and policies are administered in Alaska’s Indigenous communities.
' evidence: "Many studies have examined different aspects of Alaska’s Indigenous communities, including the ways climate change is affecting or can affect subsistence,{{< tbib '15' 'e0b0f2a6-5ac8-4196-8634-6123511e0051' >}},{{
The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.
' report_identifier: nca4 statement: 'The subsistence activities, culture, health, and infrastructure of Alaska’s Indigenous peoples and communities are subject to a variety of impacts, many of which are expected to increase in the future (likely, high confidence). Flexible, community-driven adaptation strategies would lessen these impacts by ensuring that climate risks are considered in the full context of the existing sociocultural systems (likely, medium confidence).
' uncertainties: 'There is little question that climate change is having widespread and far-reaching impacts on Alaska’s Indigenous peoples. It is less clear, however, exactly which peoples and communities are responding to the changes they face. One community may be able to seize a new opportunity or may be able to adjust effectively to at least some forms of change, whereas another community will not be able to do either. More needs to be understood about these differences, the reasons for them, and how adaptability and resilience can be fostered.
It is also unclear how, exactly, the changes will influence one another as they occur in the context of all that is happening in Alaska Native life. For example, climate change may mean hunters have to travel farther to hunt. GPS allows for more reliable navigation, and four-stroke engines provide more confidence when traveling farther offshore. At the same time, rising fuel prices mean it is more expensive to travel far, perhaps limiting the ability of a hunter to take advantage of better navigation and motors. How these competing influences will balance out is difficult to say and requires more attention.
' uri: /report/nca4/chapter/alaska/finding/key-message-26-4 url: ~ - chapter_identifier: alaska confidence: 'There is high confidence and it is very likely that future damage to infrastructure from thawing permafrost and coastal erosion will cost hundreds of millions of dollars annually to repair or replace. There is high confidence and it is likely that timely repair and maintenance of infrastructure can reduce damages and avoid some of the added costs. There is medium confidence and it is very likely that these costs will be offset in part by savings from reduced space heating needs.
' evidence: "Coastal erosion affects a number of coastal communities, with the highest rates on the Arctic coastline.{{< tbib '19' 'cf15559b-f1e8-4022-945b-45ab149dc1a8' >}} Coastal erosion and flooding in some cases will require that entire communities, or portions of communities, relocate to safer terrain. The U.S. Army Corps of Engineers identified erosion threats to 31 communities requiring partial or complete relocation.{{< tbib '123' '49a37e8f-eef6-4ee6-9705-fac54c48df30' >}} Relocation costs for seven vulnerable communities identified in a 2009 U.S. Government Accountability Office (GAO) study ranged from $80 to $200 million per community.{{< tbib '122' '1807de04-16a3-422a-a5bc-d241def97f88' >}}
Melting glaciers will increase the role of seasonal precipitation patterns for hydroelectric power generation. River discharge has been increasing during the winter since the 1960s, but because reservoirs are generally full in fall, investments to increase reservoir heights would be required to take advantage of increased fall precipitation.{{< tbib '145' '09961450-e217-4cf4-b11f-fab19c8ea9ed' >}}
National Weather Service (NWS) daily weather summaries show that heating degree days have already declined by 5% in Sitka, 6% in Fairbanks and Nome, and 8% in Anchorage and Utqiaġvik (formally known as Barrow) as compared to mid-20th century levels. The same NWS data show that increased cooling degree days from warmer summer temperatures provide only a small offset to the beneficial effect of lower heating costs.
" href: https://data.globalchange.gov/report/nca4/chapter/alaska/finding/key-message-26-5.yaml identifier: key-message-26-5 ordinal: 5 process: 'The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.
' report_identifier: nca4 statement: 'Climate warming is causing damage to infrastructure that will be costly to repair or replace, especially in remote Alaska (very likely, high confidence). It is also reducing heating costs throughout the state (likely, medium confidence). These effects are very likely to grow with continued warming (very likely, high confidence). Timely repair and maintenance of infrastructure can reduce the damages and avoid some of these added costs (likely, high confidence).
' uncertainties: 'The extent, rate, and patterns of coastal erosion at locations other than along the north coast, and including deltas and rivers, are poorly known. Change in the patterns and trends of erosion (for example, an increase in the rate associated with warming and climate change), is expected but poorly documented for most locations due to the scarcity of historical data.
Future energy prices are highly uncertain, generating a high level of uncertainty around the dollar value of the savings in space heating costs associated with the projected decline in heating degree days.
Wildfire suppression costs depend on future policy decisions for wildfire management. Property damage from wildfire depends on uncertain future settlement and development patterns.
' uri: /report/nca4/chapter/alaska/finding/key-message-26-5 url: ~ - chapter_identifier: alaska confidence: 'There is high confidence that proactive adaptation can reduce costs, generate social and economic opportunity, and improve livelihood security. It is likely and there is high confidence that proactive adaptation will be affected by external factors, such as global markets that are beyond the control of the organization or institution implementing the adaptations.
It is likely and there is very high confidence that direct engagement and partnership with communities will be a critical element of adaptation success, as this has strong evidence and high consensus in the literature; however, there are a limited number of publications that document this partnership model in Alaska.
' evidence: "Research investigating costs of adapting to projected climate changes in Alaska in the realms of public infrastructure and wildfire suppression indicates cost savings from adaptation.{{< tbib '21' 'b7e764c8-8912-4d18-8dd3-1555ab8da1c2' >}},{{
Adaptation actions to the impacts of climate change in Alaska have been transitioning from awareness and concern to education and actions.{{< tbib '135' 'b8ad073b-11cd-4b02-809d-f992e02566b4' >}},{{
Most research reports on case studies and actions that describe transparent, collaborative, and accessible information though data sharing, building of networks, and long-term partnerships with communities.{{< tbib '252' '46337d79-86c4-4e77-bab9-724c5f44c63f' >}},{{
A number of climate adaptation guidebooks focus on Alaska and Canada, which have related adaptation challenges.{{< tbib '134' 'f3fa0761-8412-46f5-9da4-b9b467bd8521' >}} Universities, governments, and nongovernmental organizations produced these guidebooks for a range of audiences, including rural Alaska Native communities, local governments, and state governments. Key phases in the adaptation planning process that are consistent across the majority of the guidebooks include building partnerships and networks of stakeholders; conducting vulnerability and risk assessments; establishing priorities, options, and an implementation plan and evaluation metrics; implementing the preferred option; and conducting ongoing monitoring and adjustment of activities.{{< tbib '134' 'f3fa0761-8412-46f5-9da4-b9b467bd8521' >}} Guidebooks specific to Alaska Natives and Canadian Inuit and First Nations peoples emphasize the importance of community support and participation in the adaptation planning process.{{< tbib '134' 'f3fa0761-8412-46f5-9da4-b9b467bd8521' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/alaska/finding/key-message-26-6.yaml identifier: key-message-26-6 ordinal: 6 process: 'The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.
' report_identifier: nca4 statement: 'Proactive adaptation in Alaska would reduce both short- and long-term costs associated with climate change, generate social and economic opportunity, and improve livelihood security (likely, high confidence). Direct engagement and partnership with communities is a vital element of adaptation in Alaska (likely, very high confidence).
' uncertainties: "Little research has been conducted to track and evaluate the efficacy of implementation of existing adaptation planning in Alaska or to assess the possibilities for maladaptation. Similarly, the feedbacks and synergies are not well documented between adaptation and changes in physical, natural, and social systems. More research is needed to understand cross-sector and cumulative impacts and how they can best be addressed in an all-inclusive manner.{{< tbib '135' 'b8ad073b-11cd-4b02-809d-f992e02566b4' >}}
" uri: /report/nca4/chapter/alaska/finding/key-message-26-6 url: ~ - chapter_identifier: hawaii-and-pacific-islands confidence: 'There is very high confidence in further increases in temperature in the region, based on the consistent results of global climate models showing continued significant increases in temperature in the Hawai‘i–USAPI region for all plausible emissions scenarios.
There is low confidence regarding projected changes in precipitation patterns, stemming from the divergent results of global models and downscaling approaches and from uncertainties around future emissions. However, for leeward areas of Hawai‘i and the eastern part of the Federated States of Micronesia (FSM), future decreases in precipitation are somewhat more likely, based on greater agreement between downscaling approaches for Hawai‘i and greater agreement among global models for eastern FSM.
There is very high confidence in future increases in sea level, based on widely accepted evidence that warming will increase global sea level, with amplified effects in the low latitudes.
There is medium confidence in the increasing risk of both drought and flood extremes patterns, based on both observed changes (for example, increasing lengths of wet and dry periods) and projected effects of warming on extreme weather globally.
There is medium confidence in possible future catastrophic impacts on food and water security resulting from saltwater contamination in low atolls due to sea level rise; this is based on very high confidence in continuing sea level rise, the known effects of saltwater contamination on water supply and agriculture, and uncertainty regarding the effectiveness of adaptation measures.
' evidence: "Vulnerability of water supplies to climate change: With their isolation and limited land areas, Hawai‘i and the USAPI are vulnerable to the effects of climate change on water supplies.{{< tbib '72' '97ae6e5b-3482-4760-a4f4-9e00ee6337b6' >}},{{
Temperature change: In Hawai‘i, air temperature increased by 0.76°F (0.42°C) over the past 100 years. The year 2015 was the warmest on record at 1.43°F (0.79°C) above the 100-year average. Mean and minimum (nighttime) temperatures both show long-term, statistically significant increasing trends, while the diurnal temperature range (the average difference between daily minimum and maximum temperature) shows a long-term, statistically significant decreasing trend.{{< tbib '59' '7621e6f5-4234-4a44-bb1d-8278429deb2b' >}} Estimates of historical temperature changes in Hawai‘i are based on the relatively few observing stations with long records and represent the best available data. Further temperature increases in the Hawai‘i–USAPI region are highly likely. Northern tropical Pacific (including Micronesia) sea level air temperatures are expected to increase by 2.2°–2.7°F (1.2°–1.5°C) by mid-century and by 2.7°–5.9°F (1.5°–3.3°C) by 2100.{{< tbib '63' '1fca63fb-3033-445e-99ba-1136da451058' >}} Southern tropical Pacific (including American Sāmoa) sea level air temperatures are expected to increase by 1.8°–3.1°F (1.0°–1.7°C) by mid-century and by 2.5°–5.8°F (1.4°–3.2°C) by 2100.{{< tbib '63' '1fca63fb-3033-445e-99ba-1136da451058' >}} Increasing temperatures throughout the Hawai‘i–USAPI region might cause increases in potential evapotranspiration,{{< tbib '226' 'bdbb00c1-6c40-4e03-9120-2df759b580a7' >}} with consequent negative impacts on water supplies.
Precipitation change: While Hawai‘i precipitation has experienced upward and downward changes across a range of timescales, more than 90% of the state had a net downward rainfall trend during 1920–2012.{{< tbib '60' 'e6d1098e-93cc-4285-9d16-6e52c5e302f7' >}} Projections of future precipitation changes in Hawai‘i are still uncertain. Using a dynamical downscaling approach to project climate changes in Hawai‘i for the 20-year period at the end of the this century under a middle-of-the-road scenario (SRES A1B) resulted in increases in mean annual rainfall of up to 30% in the wet windward areas of Hawaiʻi and Maui Islands and decreases of 40% in some of the dry leeward and high-elevation interior areas.{{< tbib '34' 'f60beed2-efd0-40c8-8f94-b81d3e9f1509' >}} Somewhat different results were obtained using an independent statistical downscaling method.{{< tbib '34' 'f60beed2-efd0-40c8-8f94-b81d3e9f1509' >}} For the lower scenario (RCP4.5), mean annual rainfall in Hawai‘i is projected by statistical downscaling to have only small changes in windward areas of Hawai‘i and Maui Islands, to decrease by 10%–20% in windward areas of the other islands, and to decrease by up to 60% in leeward areas for the period 2041–2070. For the same scenario, the late-century (2071–2100) projection is similar to the 2041–2070 projection, except that a larger portion of the leeward areas will experience reductions of 20%–60%. For the higher scenario (RCP8.5), windward areas of Hawai‘i and Maui Islands will see changes between +10% and −10%, and rainfall in leeward areas will decrease by 10% to more than 60% by the 2041–2070 period. By the late-century period (2071–2100), windward areas of Hawai‘i and Maui Islands will see increases of up to 20%, windward areas on other islands will have decreases of 10% to 30%, and leeward areas will have decreases of 10% to more than 60%. The number of climate and water resources monitoring stations has declined across the region,{{< tbib '23' '7350d7b3-6e95-4375-ba23-26756b441fc2' >}},{{
Trends in hydrological extremes in Hawai‘i: Increasing trends in extreme 30-day rainfall and the lengths of consecutive dry-day and consecutive wet-day periods{{< tbib '66' 'f8ccfb79-1bed-462d-9172-c56a71b542b9' >}} indicate that Hawai‘i’s rainfall is becoming more extreme and suggest that both droughts and floods are becoming more frequent in Hawai‘i. With the addition of more years of observed data, and a more detailed spatiotemporal analysis from a grid-box level down to the island level, this contrasts with the earlier findings of a decreasing trend in the number of extreme rainfall events in Hawai‘i.{{< tbib '227' '39d80273-7b1f-4342-8c9d-439e262dea4f' >}}
Saltwater contamination due to sea level rise: Sea level rise exacerbates the existing vulnerability of groundwater lenses on small coral islands to contamination by saltwater intrusion by amplifying the impacts of freshwater lens-shrinking droughts and storm-related overwash events.{{< tbib '69' 'dc90f15e-2420-461e-ba38-f65717485591' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-1.yaml identifier: key-message-27-1 ordinal: 1 process: "To frame this chapter, the regional leads wanted to maximize inclusiveness and represent the key sectoral interests of communities and researchers. To select sectors and a full author team, the coordinating lead author and regional chapter lead author distributed an online Google survey from September to October 2016. The survey received 136 responses representing Hawaiʻi and all the U.S.-Affiliated Pacific Islands (USAPI) jurisdictions; respondents identified which of the National Climate Assessment (NCA) sectors they were most interested in learning about with respect to climate change in the Pacific Islands and suggested representative case studies.{{< tbib '223' '884675c9-3e31-483d-b6b9-fd53b99875ae' >}} The five top sectors were picked as the focus of the chapter, and a total of eight lead authors with expertise in those sectors were invited to join the regional team. To solicit additional participation from potential technical contributors across the region, two informational webinars spanning convenient time zones across the Pacific were held; 35 people joined in. The webinars outlined the NCA history and process, as well as past regional reports and ways to participate in this Fourth National Climate Assessment (NCA4).
A critical part of outlining the chapter and gathering literature published since the Third National Climate Assessment (NCA3){{< tbib '224' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} was done by inviting technical experts in the key sectors to participate in a half-day workshop led by each of the lead authors. A larger workshop centered on adaptation best practices was convened with participants from all sectors, as well as regional decision-makers. In all, 75 participants, including some virtual attendees, took part in the sectoral workshops on March 6 and 13, 2017. Finally, to include public concerns and interests, two town hall discussion events on March 6 and April 19, 2017, were held in Honolulu, Hawaiʻi, and Tumon, Guam, respectively. Approximately 100 participants attended the town halls. Throughout the refining of the Key Messages and narrative sections, authors met weekly both via conference calls and in person to discuss the chapter and carefully review evidence and findings. Technical contributors were given multiple opportunities to respond to and edit sections. The process was coordinated by the regional chapter lead and coordinating lead authors, as well as the Pacific Islands sustained assessment specialist.
" report_identifier: nca4 statement: 'Dependable and safe water supplies for Pacific island communities and ecosystems are threatened by rising temperatures (very high confidence), changing rainfall patterns (low confidence), sea level rise (very high confidence), and increased risk of extreme drought and flooding (medium confidence). Islands are already experiencing saltwater contamination due to sea level rise, which is expected to catastrophically impact food and water security, especially on low-lying atolls (medium confidence). Resilience to future threats relies on active monitoring and management of watersheds and freshwater systems.
' uncertainties: "Effects of warming on evapotranspiration: There are uncertainties in how warming will affect cloud cover, solar radiation, humidity, and wind speed. All of these affect potential evapotranspiration and changes in soil moisture, and the effects will differ by region.{{< tbib '228' '44466960-d3a9-4374-b1cf-893bb8a476f0' >}}
Future precipitation changes: Global models differ in their projections of precipitation changes for the Hawai‘i–USAPI region.{{< tbib '63' '1fca63fb-3033-445e-99ba-1136da451058' >}} For Hawai‘i, downscaled projections differ according to the choice of global model time horizon, emissions scenario, and downscaling method.{{< tbib '229' '9171ec97-c44b-48eb-80b3-2756ba8a14a3' >}}
" uri: /report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-1 url: ~ - chapter_identifier: hawaii-and-pacific-islands confidence: 'It is very likely that air and water temperatures will increase and that sea level will rise (very high confidence). Research indicates that global mean sea level rise will exceed previous estimates and that, in the USAPI, sea level rise is likely to be higher than the global mean (likely, high confidence). As a result, it is likely that climate change will affect low-lying and coastal ecosystems in Hawaiʻi and other Pacific islands, with medium confidence in forecasts of the effects on these ecosystems.
There is low confidence as to how rainfall patterns will shift across the main Hawaiian Islands. It is considered likely that changes in rainfall will result in ecologic shifts expected to threaten some species. However, there is low confidence in specific ecologic forecasts because the direction and magnitude of rainfall changes are uncertain, and there is a lack of robust understanding of how species will respond to those changes. It seems as likely as not that the responses of terrestrial biomes and species to climate change will result in additional complexity in the management of rare and threatened species.
' evidence: "Projections of sea level rise have been made at both regional and local scales (see Traceable Account for Key Message 3). Based on these projections, the effects of sea level rise on coastal ecosystems have been evaluated for the Northwest Hawaiian Islands.{{< tbib '18' '8fd88741-58fd-4753-ae35-af3a2ed38915' >}},{{
Forecasts of how climate change will affect rainfall and temperature in the main Hawaiian Islands have been based on both statistical and dynamical downscaling of global climate models (GCMs; see Traceable Account for Key Message 1). Statewide vulnerability models have been developed for nearly all species of native plants{{< tbib '233' 'c0eb08ae-6725-4e68-b99e-1f2cef382c25' >}} and forest birds,{{< tbib '43' 'f483b8cf-8401-40ec-9001-23466261d5fa' >}} showing substantial changes in the available habitat for many species. More detailed modeling within Hawaiʻi Volcanoes National Park has suggested that rare and listed plants being managed in Special Ecological Areas will experience climate changes that make the habitat in these areas unsuitable.{{< tbib '91' '5eac12ba-e664-4eb2-aa66-18d9067566d8' >}}
Effects of climate change on streamflow in Hawaiʻi will largely be driven by changes in rainfall, although geologic conditions affect the discharge of groundwater that provides base flow during dry weather.{{< tbib '234' '381cc925-f22b-46a5-8a36-3e99bbd52635' >}} A regional watershed model from the windward side of Hawaiʻi Island suggested that control of an invasive tree with high water demand would somewhat mitigate decreases in streamflow that might be caused by a drier climate.{{< tbib '44' 'e69ceccd-2c27-48f0-b3fe-46ce1b67f636' >}} Finally, it has been suggested that ocean acidification will decrease the viability of the planktonic larvae of native Hawaiian stream fishes.{{< tbib '99' '0c523a5a-213e-491a-9dcf-0a2c7eb05d77' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-2.yaml identifier: key-message-27-2 ordinal: 2 process: "To frame this chapter, the regional leads wanted to maximize inclusiveness and represent the key sectoral interests of communities and researchers. To select sectors and a full author team, the coordinating lead author and regional chapter lead author distributed an online Google survey from September to October 2016. The survey received 136 responses representing Hawaiʻi and all the U.S.-Affiliated Pacific Islands (USAPI) jurisdictions; respondents identified which of the National Climate Assessment (NCA) sectors they were most interested in learning about with respect to climate change in the Pacific Islands and suggested representative case studies.{{< tbib '223' '884675c9-3e31-483d-b6b9-fd53b99875ae' >}} The five top sectors were picked as the focus of the chapter, and a total of eight lead authors with expertise in those sectors were invited to join the regional team. To solicit additional participation from potential technical contributors across the region, two informational webinars spanning convenient time zones across the Pacific were held; 35 people joined in. The webinars outlined the NCA history and process, as well as past regional reports and ways to participate in this Fourth National Climate Assessment (NCA4).
A critical part of outlining the chapter and gathering literature published since the Third National Climate Assessment (NCA3){{< tbib '224' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} was done by inviting technical experts in the key sectors to participate in a half-day workshop led by each of the lead authors. A larger workshop centered on adaptation best practices was convened with participants from all sectors, as well as regional decision-makers. In all, 75 participants, including some virtual attendees, took part in the sectoral workshops on March 6 and 13, 2017. Finally, to include public concerns and interests, two town hall discussion events on March 6 and April 19, 2017, were held in Honolulu, Hawaiʻi, and Tumon, Guam, respectively. Approximately 100 participants attended the town halls. Throughout the refining of the Key Messages and narrative sections, authors met weekly both via conference calls and in person to discuss the chapter and carefully review evidence and findings. Technical contributors were given multiple opportunities to respond to and edit sections. The process was coordinated by the regional chapter lead and coordinating lead authors, as well as the Pacific Islands sustained assessment specialist.
" report_identifier: nca4 statement: 'Pacific island ecosystems are notable for the high percentage of species found only in the region, and their biodiversity is both an important cultural resource for island people and a source of economic revenue through tourism (very high confidence). Terrestrial habitats and the goods and services they provide are threatened by rising temperatures (very likely, very high confidence), changes in rainfall (likely, medium confidence), increased storminess (likely, medium confidence), and land-use change (very likely, very high confidence). These changes promote the spread of invasive species (likely, low confidence) and reduce the ability of habitats to support protected species and sustain human communities (likely, medium confidence). Some species are expected to become extinct (likely, medium confidence) and others to decline to the point of requiring protection and costly management (likely, high confidence).
' uncertainties: 'The timing and magnitude of sea level rise are somewhat uncertain. There is greater uncertainty on how climate change will affect the complex patterns of precipitation over the high islands of Hawaiʻi. There is also high uncertainty about how plants will respond to changes in their habitats and the extent to which climate change will foster the spread of invasive species.
' uri: /report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-2 url: ~ - chapter_identifier: hawaii-and-pacific-islands confidence: 'There is very high confidence that a continued rise in global temperature will lead to increases in the rate of sea level rise. There is less confidence in the projected amounts of sea level rise during this century, and there is low confidence in the upper bounds of sea level rise by the end of the century. Sea level rise will very likely lead to saltwater intrusion, coastal erosion, and wave flooding. It is very likely this will strain the sustainability of human infrastructure systems, limit freshwater resources, and challenge food availability. If the high-end projections of future sea level rise materialize, it is very likely this will threaten the very existence of Pacific island coastal communities.
' evidence: "Multiple lines of research have shown that changes in melting in Greenland,{{< tbib '110' 'ef6eb8d0-6301-4987-a2ff-9606e1f4177a' >}} the Antarctic,{{< tbib '107' 'ae82c8a3-3033-4103-91e9-926a27d1fa18' >}} and among alpine glaciers,{{< tbib '111' '5d34229c-b521-42f4-aad1-f2ffc600879d' >}} as well as the warming of the ocean,{{< tbib '113' '6bbe13d9-4992-456c-b97d-42947994b6be' >}} have occurred faster than expected. The rate of sea level rise is accelerating,{{< tbib '103' 'd7ed19d6-e5ac-4b44-b686-0a8a16fc431b' >}} and the early signs of impact are widely documented.{{< tbib '9' '7717dd13-7f6b-4b7c-ab84-571d50f7b8da' >}} Relative to the year 2000, global mean sea level (GMSL) is very likely to rise 0.3–0.6 feet (9–18 cm) by 2030, 0.5–1.2 feet (15–38 cm) by 2050, and 1.0–4.3 feet (30–130 cm) by 2100 (very high confidence in lower bounds; medium confidence in upper bounds for 2030 and 2050; low confidence in upper bounds for 2100).{{< tbib '17' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}},{{
Changes in precipitation,{{< tbib '235' 'c57f7893-035e-49d9-b31d-83856dab8624' >}} Pacific sea level,{{< tbib '4' '6e320831-727b-482d-982a-45732be3790f' >}} climate variability,{{< tbib '3' 'e5f02380-28e9-4238-994f-09a2efba32ae' >}} and the unsustainable practices of many human communities among Pacific islands{{< tbib '127' 'f22f00d3-1456-4fef-b286-a4af1494bb93' >}} all converge to increase the vulnerability of coastal populations{{< tbib '135' 'e16534d0-638a-4fdc-88fb-426611965c54' >}} as climate change continues in the future.{{< tbib '55' 'a9307aae-3eb6-41f2-9921-ba96fa8ac075' >}} As sea level rises and average atmospheric temperature continues to increase, wave events{{< tbib '37' '1b9a155a-3d54-41ff-a844-1400bb326927' >}} associated with changing weather patterns{{< tbib '140' 'fc838fdf-81d0-488b-a2b5-0781d7bbc9ef' >}} constitute a growing mechanism for delivering{{< tbib '12' 'f4859f1b-a4d7-4e21-a05b-70204fd6df59' >}} damaging saltwater into island aquifer systems,{{< tbib '13' '88dcd306-5ae7-48df-8411-658f9c5d97bc' >}} ecosystems,{{< tbib '129' 'd055c0df-2c85-4ee1-a3c6-8e6c79e425bd' >}} and human infrastructure systems.{{< tbib '17' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}}
In Hawaiʻi, studies by the Hawaiʻi Climate Change Mitigation and Adaptation Commission{{< tbib '42' '0244c888-89df-4a3c-a7f1-79af0a0a6f00' >}} reveal that with 3.2 feet of sea level rise, over 25,800 acres of land in the state would be rendered unusable. Some of that land would erode into the ocean, some would become submerged by inches or feet of standing water, and some areas would be dry most of the year but repeatedly washed over by seasonal high waves. Statewide, about 34% of that potentially lost land is designated for urban use, 25% is designated for agricultural use, and 40% is designated for conservation. The loss of urban land is expected to increase pressure on the development of inland areas, including those designated as agricultural and conservation lands. Across the state, over 6,500 structures located near the shoreline would be compromised or lost with 3.2 feet of sea level rise. Some of these vulnerable structures include houses and apartment buildings, and their loss would result in over 20,000 displaced residents in need of new homes. The value of projected flooded structures, combined with the land value of the 25,800 acres projected to be flooded, amounts to over $19 billion across the state (in 2013 dollars; $19.6 billion in 2015 dollars). However, this figure does not encompass the full loss potential in the state, as monetary losses that would occur from the chronic flooding of roads, utilities, and other public infrastructure were not analyzed in this report and are expected to amount to as much as an order of magnitude greater than the potential economic losses from land and structures. For example, over 38 miles of major roads would be chronically flooded across the state with 3.2 feet of sea level rise. Utilities, such as water, wastewater, and electrical systems, often run parallel and underneath roadways, making lost road mileage a good indication of the extent of lost utilities. This chronic flooding of infrastructure would have significant impacts on local communities as well as reverberating effects around each island.
The loss of valuable natural and cultural resources across all islands would cost the state dearly, due to their intrinsic value. Beaches that provide for recreation, wildlife habitat, and cultural tradition would erode, from iconic sites such as Sunset Beach on O‘ahu to neighborhood beach access points rarely visited by anyone except local residents. Some beaches would be lost entirely if their landward migration is blocked by roads, structures, shoreline armoring, or geology. The flooding of the more than 2,000 on-site sewage disposal systems with 3.2 feet of sea level rise would result in diminished water quality in streams and at beaches and shoreline recreation areas. The loss of and harm to native species and entire ecosystems would have implications for Hawaiian cultural traditions and practices, which are closely tied to the natural environment. Further, nearly 550 cultural sites in the state would be flooded, and many Hawaiian Home Lands communities would be impacted by flooding. In some cases, inland migration or careful relocation of these natural and cultural resources is expected to be possible. In other cases, the resources are inextricably bound to place and would be permanently altered by flooding.{{< tbib '42' '0244c888-89df-4a3c-a7f1-79af0a0a6f00' >}}
Marra and Kruk (2017){{< tbib '142' 'a4512dba-212b-4139-b4bd-7dcdc5632f03' >}} describe climate trends for the USAPI. Globally and locally, observations of GHG concentrations, surface air temperatures, sea level, sea surface temperature, and ocean acidification show rising trends at an increasing rate. Trends in measures of rainfall, surface winds, and tropical cyclones are not as readily apparent. Patterns of climate variability characterize these measures and tend to mask long-term trends. A lack of high-quality, long-term observational records, particularly with respect to in situ stations, contributes to difficulties in discerning trends. To maintain and enhance our ability to assess environmental change, attention needs to be given to robust and sustained monitoring.
There are consistent subregional changes in the number of days with high winds. The global frequency of tropical cyclones (TCs) appears to be showing a slow downward trend since the early 1970s. In the Pacific region, long-term TC trends in frequency and intensity are relatively flat, with the record punctuated by as many active as inactive years.{{< tbib '142' 'a4512dba-212b-4139-b4bd-7dcdc5632f03' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-3.yaml identifier: key-message-27-3 ordinal: 3 process: "To frame this chapter, the regional leads wanted to maximize inclusiveness and represent the key sectoral interests of communities and researchers. To select sectors and a full author team, the coordinating lead author and regional chapter lead author distributed an online Google survey from September to October 2016. The survey received 136 responses representing Hawaiʻi and all the U.S.-Affiliated Pacific Islands (USAPI) jurisdictions; respondents identified which of the National Climate Assessment (NCA) sectors they were most interested in learning about with respect to climate change in the Pacific Islands and suggested representative case studies.{{< tbib '223' '884675c9-3e31-483d-b6b9-fd53b99875ae' >}} The five top sectors were picked as the focus of the chapter, and a total of eight lead authors with expertise in those sectors were invited to join the regional team. To solicit additional participation from potential technical contributors across the region, two informational webinars spanning convenient time zones across the Pacific were held; 35 people joined in. The webinars outlined the NCA history and process, as well as past regional reports and ways to participate in this Fourth National Climate Assessment (NCA4).
A critical part of outlining the chapter and gathering literature published since the Third National Climate Assessment (NCA3){{< tbib '224' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} was done by inviting technical experts in the key sectors to participate in a half-day workshop led by each of the lead authors. A larger workshop centered on adaptation best practices was convened with participants from all sectors, as well as regional decision-makers. In all, 75 participants, including some virtual attendees, took part in the sectoral workshops on March 6 and 13, 2017. Finally, to include public concerns and interests, two town hall discussion events on March 6 and April 19, 2017, were held in Honolulu, Hawaiʻi, and Tumon, Guam, respectively. Approximately 100 participants attended the town halls. Throughout the refining of the Key Messages and narrative sections, authors met weekly both via conference calls and in person to discuss the chapter and carefully review evidence and findings. Technical contributors were given multiple opportunities to respond to and edit sections. The process was coordinated by the regional chapter lead and coordinating lead authors, as well as the Pacific Islands sustained assessment specialist.
" report_identifier: nca4 statement: 'The majority of Pacific island communities are confined to a narrow band of land within a few feet of sea level. Sea level rise is now beginning to threaten critical assets such as ecosystems, cultural sites and practices, economics, housing and energy, transportation, and other forms of infrastructure (very likely, very high confidence). By 2100, increases of 1–4 feet in global sea level are very likely, with even higher levels than the global average in the U.S.-Affiliated Pacific Islands (very likely, high confidence). This would threaten the food and freshwater supply of Pacific island populations and jeopardize their continued sustainability and resilience (likely, high confidence). As sea level rise is projected to accelerate strongly after mid-century, adaptation strategies that are implemented sooner can better prepare communities and infrastructure for the most severe impacts.
' uncertainties: 'Major uncertainties lie in understanding and projecting the future melting behavior of the Antarctic and Greenland ice sheets. To date, new observations attest to melting occurring at higher than expected rates. If this continues to be the case, it is plausible for future sea level rise to exceed even worst-case scenarios. Secondary feedbacks to warming, such as changes in the global thermohaline circulation; shifts in major weather elements, such as the intertropical convergence zone and the polar jet stream; and unexpected modes of heat distribution across the hemispheres risk complex responses in the climate system that are not well understood. Pacific climate variability is a governing element that amplifies many aspects of climate change, such as drought, sea level, storminess, and ocean warming. A number of mechanisms through which climate change might alter Pacific variability have been proposed on the basis of physical modeling, but our understanding of the variability remains low, and confidence in projected changes is also low. For instance, in any given Pacific region, our understanding of future TC occurrence, intensity, and frequency is low. Future physical responses to climate change that have not yet been described are possible. These uncertainties greatly limit our ability to identify the chronology of changes to expect in the future.
' uri: /report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-3 url: ~ - chapter_identifier: hawaii-and-pacific-islands confidence: 'There is high confidence that fisheries and the livelihoods they support are threatened by warmer ocean temperatures and ocean acidification. Widespread and multiyear coral reef bleaching and mortality are already occurring. It is likely, based on modeled SST projections, that by mid-century, bleaching will occur annually with associated mortality.
There is medium confidence in the projection of annual bleaching by mid-century, as it does not take into account any adaptation in corals.
There is high confidence that bleaching and rising seawater acidity will result in loss of reef structure, leading to lower fisheries yields and loss of coastal protection. This is deemed very likely because significant coral mortality has recently been observed in western Hawaiian coral reefs that suffered from the 2015 bleaching event. Further, the positive relationship between fish density and coral reef cover is well established. The magnitude of this impact depends on the extent that coral species exhibit adaptive or resilience capacity.
There is medium confidence that declines in oceanic fishery productivity of up to 15% and 50% are likely by mid-century and 2100, respectively. These declines are considered likely because we have seen related linkages between climate variability such as ENSO and the Pacific Decadal Oscillation and fisheries yields that provide an analog in some ways to global warming impacts. The uncertainty lies in our limited understanding of the linkages and feedbacks in the very complex oceanic food web. As temperate habitats warm, they will likely gain some tropical species, while the tropical habitats will likely only lose species.
' evidence: "The Key Message was developed based on input from an expert working group convened at the outset of this section development and supported by extensive literature.
Ocean warming: NCA3 documented historical increases in sea surface temperature (SST), and current levels in much of the region have now exceeded the upper range of background natural variation.{{< tbib '32' '081bdbe7-f95f-4708-b18c-e7bc797effa7' >}},{{
Ocean acidification: Atmospheric carbon dioxide levels recorded at Mauna Loa, Hawaiʻi, have recently exceeded 400 parts per million, and oceanic pH levels measured off Oʻahu have steadily declined from an annual average of about 8.11 to 8.07 over the past 25 years (data from Hawaiʻi Ocean Time Series, SOEST, University of Hawaiʻi) and are projected to decrease to 7.8 by 2100.{{< tbib '123' 'fa5d3ea3-a0ad-4418-b516-20c748528b2f' >}} As pH declines, it lowers the saturation level of aragonite (the form of calcium carbonate used by corals and many other marine organisms), reducing coral and shell growth.{{< tbib '125' '7ab1d9e1-75a1-48c5-8d85-02258496f919' >}} By the end of the century, aragonite saturation is projected to decline from a current level of 3.9 to 2.4, representing extremely marginal conditions for coral reef growth.{{< tbib '32' '081bdbe7-f95f-4708-b18c-e7bc797effa7' >}},{{
Bleaching events: These continue to occur—most recently over successive years—with widespread impacts.{{< tbib '45' 'be538e70-7c97-4680-a580-7ee398361090' >}},{{
Mortality: During the 2014–2015 bleaching events, coral mortality in western Hawaiʻi was estimated at 50%{{< tbib '45' 'be538e70-7c97-4680-a580-7ee398361090' >}} and over 90% at the pristine equatorial Jarvis Atoll.{{< tbib '156' '71443a23-b42f-4435-93ac-78d32df5bd30' >}}
Coral reef ecosystem impacts: Coral reef cover around the Pacific Islands region is projected to decline from the current average level of about 40% to 15%–30% by 2035 and 10%–20% by 2050.{{< tbib '123' 'fa5d3ea3-a0ad-4418-b516-20c748528b2f' >}} The loss of coral reef habitat is projected to reduce fish abundance and fisheries yields by 20%.{{< tbib '123' 'fa5d3ea3-a0ad-4418-b516-20c748528b2f' >}} Loss of coral reefs will result in increased coastal erosion.{{< tbib '23' '7350d7b3-6e95-4375-ba23-26756b441fc2' >}},{{
Insular fisheries: Insular fishes, including both coral reef fishes and more mobile, coastal pelagics (species such as mahi mahi and wahoo), are impacted both from declines in carrying capacity and loss from migration in response to temperature change. Taken together, declines in maximum catch potential exceeding 50% from late 20th century levels under the higher scenario are projected by 2100 for the exclusive economic zones of most islands in the central and western Pacific.{{< tbib '163' 'faaa3555-cab7-44a6-a71e-dc269d1b67ce' >}}
Oceanic fisheries: A number of studies have projected that ocean warming will result in lower primary productivity due to increased vertical stratification and loss of biodiversity as organisms move poleward.{{< tbib '129' 'd055c0df-2c85-4ee1-a3c6-8e6c79e425bd' >}},{{
To frame this chapter, the regional leads wanted to maximize inclusiveness and represent the key sectoral interests of communities and researchers. To select sectors and a full author team, the coordinating lead author and regional chapter lead author distributed an online Google survey from September to October 2016. The survey received 136 responses representing Hawaiʻi and all the U.S.-Affiliated Pacific Islands (USAPI) jurisdictions; respondents identified which of the National Climate Assessment (NCA) sectors they were most interested in learning about with respect to climate change in the Pacific Islands and suggested representative case studies.{{< tbib '223' '884675c9-3e31-483d-b6b9-fd53b99875ae' >}} The five top sectors were picked as the focus of the chapter, and a total of eight lead authors with expertise in those sectors were invited to join the regional team. To solicit additional participation from potential technical contributors across the region, two informational webinars spanning convenient time zones across the Pacific were held; 35 people joined in. The webinars outlined the NCA history and process, as well as past regional reports and ways to participate in this Fourth National Climate Assessment (NCA4).
A critical part of outlining the chapter and gathering literature published since the Third National Climate Assessment (NCA3){{< tbib '224' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} was done by inviting technical experts in the key sectors to participate in a half-day workshop led by each of the lead authors. A larger workshop centered on adaptation best practices was convened with participants from all sectors, as well as regional decision-makers. In all, 75 participants, including some virtual attendees, took part in the sectoral workshops on March 6 and 13, 2017. Finally, to include public concerns and interests, two town hall discussion events on March 6 and April 19, 2017, were held in Honolulu, Hawaiʻi, and Tumon, Guam, respectively. Approximately 100 participants attended the town halls. Throughout the refining of the Key Messages and narrative sections, authors met weekly both via conference calls and in person to discuss the chapter and carefully review evidence and findings. Technical contributors were given multiple opportunities to respond to and edit sections. The process was coordinated by the regional chapter lead and coordinating lead authors, as well as the Pacific Islands sustained assessment specialist.
" report_identifier: nca4 statement: 'Fisheries, coral reefs, and the livelihoods they support are threatened by higher ocean temperatures and ocean acidification (very likely, high confidence).Widespread coral reef bleaching and mortality have been occurring more frequently, and by mid-century these events are projected to occur annually, especially if current trends in emissions continue (likely, medium confidence). Bleaching and acidification will result in loss of reef structure, leading to lower fisheries yields, and loss of coastal protection and habitat (very likely, very high confidence). Declines in oceanic fishery productivity of up to 15% and 50% of current levels are projected by mid-century and 2100, respectively, under the higher scenario (RCP8.5; likely, medium confidence).
' uncertainties: "A major uncertainty for coral reefs is whether they can evolve rapidly enough to keep up with the changing temperature and pH.{{< tbib '164' '06b7a4b5-9c7e-42de-8dee-c54d443a2af3' >}},{{
There is high confidence that climate change is having far-reaching effects on the land security, livelihood security, habitat security, and cultural food security of Indigenous peoples of the Pacific.
It is likely that most of these impacts will have negative effects on the cultural heritage of the Pacific island communities.
There is high confidence that traditional knowledge together with science will support the adaptive capacity of Pacific island communities to survive on their islands.
' evidence: "The research supporting this Key Message examines the impacts of climate change on the lands, territories, and resources of the Pacific region and its Indigenous communities.
It is foundational to highlight the interconnectedness and important familial relationship Indigenous peoples have with their lands, territories, and resources. Native Hawaiian attorneys and professors Sproat and Akutagawa discuss the health impacts and threats that climate change poses for Indigenous communities and their relationship with ancestral resources. Sproat states that “any such loss will result in the loss of culture.”{{< tbib '177' '9c017401-c8d2-4d9f-9d69-4a7bb247594b' >}} Further support is found in a community health assessment done by Akutagawa and others that states, “In traditional Hawaiian conceptions of health, personal harmony and well-being are deemed to stem from one’s relationship with the land, sea, and spiritual world”.{{< tbib '176' '85e07f9f-b899-4b21-8028-3a9c2d85d792' >}}
Governments and their support institutions are also sharing outcomes of projects they’ve initiated over the years that document not only the successes but also the challenges, observations, and lessons learned.{{< tbib '149' '567b51b3-07f8-4e75-81d5-76b394218947' >}},{{
In writing this Key Message, the authors considered the body of research focusing on the impacts of climate change on Pacific communities such as sea level rise,{{< tbib '104' 'b36fdfcb-d735-4cad-a0df-806725e7d8f4' >}},{{
There is very strong evidence that traditional knowledge is key to the resilience and adaptive capacity of Indigenous peoples of the Pacific.{{< tbib '21' '5db43854-3226-408c-a5ef-aa7898146f1f' >}},{{
To frame this chapter, the regional leads wanted to maximize inclusiveness and represent the key sectoral interests of communities and researchers. To select sectors and a full author team, the coordinating lead author and regional chapter lead author distributed an online Google survey from September to October 2016. The survey received 136 responses representing Hawaiʻi and all the U.S.-Affiliated Pacific Islands (USAPI) jurisdictions; respondents identified which of the National Climate Assessment (NCA) sectors they were most interested in learning about with respect to climate change in the Pacific Islands and suggested representative case studies.{{< tbib '223' '884675c9-3e31-483d-b6b9-fd53b99875ae' >}} The five top sectors were picked as the focus of the chapter, and a total of eight lead authors with expertise in those sectors were invited to join the regional team. To solicit additional participation from potential technical contributors across the region, two informational webinars spanning convenient time zones across the Pacific were held; 35 people joined in. The webinars outlined the NCA history and process, as well as past regional reports and ways to participate in this Fourth National Climate Assessment (NCA4).
A critical part of outlining the chapter and gathering literature published since the Third National Climate Assessment (NCA3){{< tbib '224' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} was done by inviting technical experts in the key sectors to participate in a half-day workshop led by each of the lead authors. A larger workshop centered on adaptation best practices was convened with participants from all sectors, as well as regional decision-makers. In all, 75 participants, including some virtual attendees, took part in the sectoral workshops on March 6 and 13, 2017. Finally, to include public concerns and interests, two town hall discussion events on March 6 and April 19, 2017, were held in Honolulu, Hawaiʻi, and Tumon, Guam, respectively. Approximately 100 participants attended the town halls. Throughout the refining of the Key Messages and narrative sections, authors met weekly both via conference call and in person to discuss the chapter and carefully review evidence and findings. Technical contributors were given multiple opportunities to respond to and edit sections. The process was coordinated by the regional chapter lead and coordinating lead authors, as well as the Pacific Islands sustained assessment specialist.
" report_identifier: nca4 statement: 'Indigenous peoples of the Pacific are threatened by rising sea levels, diminishing future freshwater availability, and shifting ecosystem services. These changes imperil communities’ health, well-being, and modern livelihoods, as well as their familial relationships with lands, territories, and resources (likely, high confidence). Built on observations of climatic changes over time, the transmission and protection of traditional knowledge and practices, especially via the central role played by Indigenous women, are intergenerational, place-based, localized, and vital for ongoing adaptation and survival.
' uncertainties: 'There is no doubt that Indigenous communities of the Pacific are being impacted by climate change. However, the rate and degree of the impacts on the spiritual, relational, and ancestral connectedness varies from community to community and on the type of practice being impacted. This variable is difficult to document and express in certain circumstances. Additionally, the degree of the impact varies according to the livelihoods of the community and the specific climatic and socioeconomic and political circumstances of the island in question.
' uri: /report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-5 url: ~ - chapter_identifier: hawaii-and-pacific-islands confidence: 'There is medium confidence that climate change will yield compounding economic, environmental, social, and cultural costs. There is greater evidence of these compounding costs resulting from extreme events that are exacerbated by climate change.
There is high confidence that food and water insecurity will result in severe disruptions to livelihoods, including the displacement and relocation of island communities.
It is likely that the absence of interventions will result in the costly and lengthy rebuilding of communities and livelihoods and more displacement and relocation. Events have played out repeatedly across the region and have resulted in damage, disruptions, and displacements.
' evidence: "For Atlantic and eastern North Pacific hurricanes and western North Pacific typhoons, increases are projected in precipitation rates and intensity. The frequency of the most intense of these storms is projected to increase in the western North Pacific and in the eastern North Pacific (see also Key Message 3).{{< tbib '246' '52ce1b63-1b04-4728-9f1b-daee39af665e' >}} Studies indicate that Hawaiʻi will see an increased frequency of tropical cyclones (TCs) due to storm tracks shifting northward in the central North Pacific.{{< tbib '40' '9082a92d-e1be-4346-8657-7b172a8f91bc' >}},{{
The Climate Science Special Report (CSSR) summarizes extensive evidence that is documented in the climate science literature and is similar to statements made in NCA3 and international{{< tbib '106' 'f03117be-ccfe-4f88-b70a-ffd4351b8190' >}} assessments.{{< tbib '33' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}} More recent downscaling studies have further supported these assessments,{{< tbib '248' '4f1e7aa1-0c36-4220-ac77-7d55bcb33061' >}} though pointing out that the changes (future increased intensity and TC precipitation rates) will not necessarily occur in all basins.{{< tbib '246' '52ce1b63-1b04-4728-9f1b-daee39af665e' >}}
Damage from TCs is significant. Tropical Cyclone Evan struck Sāmoa in December 2012 and caused damage and losses of approximately $210 million dollars (dollar year not reported), representing 30% of its annual gross domestic product (GDP). Tropical Cyclone Pam struck Vanuatu, Tuvalu, and Kiribati in 2015; in Vanuatu, it killed 11 people and caused approximately $450 million (dollar year not reported) in damages and losses, equal to 64% of GDP.{{< tbib '196' '08f6548b-e879-45a6-97df-3790e804e73e' >}}
In the CSSR, future relative sea level rise as shown for the 3.3-feet (1 m) Interagency scenario in 2100 indicates that, because they are far from all glaciers and ice sheets, relative sea level rise in Hawai‘i and other Pacific islands due to any source of melting land ice is amplified by the static-equilibrium effects. Static-equilibrium effects on sea level are produced by the gravitational, elastic, and rotational effects of mass redistribution resulting from ice loss.{{< tbib '105' '3bae2310-7572-47e2-99a4-9e4276764934' >}}
Sea level rise across Hawaiʻi is projected to rise another 1–3 feet by the end of this century. Sea level rise has caused an increase in high tide floods associated with nuisance-level impacts. High tide floods are events in which water levels exceed the local threshold (set by the National Oceanic and Atmospheric Administration’s National Weather Service) for minor impacts. These events can damage infrastructure, cause road closures, and overwhelm storm drains. Along the Hawaiian coastline, the number of tidal flood days (all days exceeding the nuisance-level threshold) has also increased, with the greatest number occurring in 2002–2003. Continued sea level rise will present major challenges to Hawaiʻi’s coastline through coastal inundation and erosion. Seventy percent of Hawaiʻi’s beaches have already been eroded over the past century, with more than 13 miles of beach completely lost. Sea level rise will also affect Hawai‘i’s coastal storm water and wastewater management systems and is expected to cause extensive economic impacts through ecosystem damage and losses in property, tourism, and agriculture.{{< tbib '247' '2eff8dd3-b0da-474d-b7be-ba223baa8396' >}}
In the Pacific Islands region, population, urban centers, and critical infrastructure are concentrated along the coasts. This results in significant damages during inundation events. In December 2008, wind waves generated by extratropical cyclones, exacerbated by sea level rise, caused a series of inundation events in five Pacific island nations.{{< tbib '9' '7717dd13-7f6b-4b7c-ab84-571d50f7b8da' >}} An area of approximately 3,000 km in diameter was affected, impacting approximately 100,000 people. Across the islands, major infrastructure damage and crop destruction resulted, costing millions of dollars and impacting livelihoods, food security, and freshwater resources.
The increases in the frequency and intensity of climate change hazards, including cyclones, wind, rainfall, and flooding, pose an immediate danger to the Pacific Islands region. A decrease in the return times of extreme events, which will reduce the ability of systems to recover, will likely cause long-term declines in welfare.{{< tbib '181' 'dd36c0e3-b849-46c9-8685-dd76a465223a' >}} For small islands states, the damage costs of sea level rise are large in relation to the size of their economies.{{< tbib '194' '2e8e659c-1150-4516-b2c2-fd3176f9c641' >}},{{
The social science research on climate and conflict suggests a possible association between climate variability and change and conflict. Consensus or conclusive evidence of a causal link remains elusive. Hsiang et al. (2013){{< tbib '249' '6013994a-8717-4a99-935a-8a13800fcdc5' >}} find strong causal evidence linking climatic events to human conflict across a range of spatial scales and time periods and across all major regions of the world. They further demonstrate that the magnitude of climate influence is substantial.{{< tbib '249' '6013994a-8717-4a99-935a-8a13800fcdc5' >}} Specifically, large deviations from average precipitation and mild temperatures systematically increase the risk of many types of conflict (intergroup to interpersonal), often substantially. Hsiang and Burke (2014){{< tbib '250' 'e3a15302-b1ec-4bfe-9ac3-3a2cf23d3303' >}} describe their detailed meta-analysis, examining 50 rigorous quantitative studies, and find consistent support for a causal association between climatological changes and various conflict outcomes.{{< tbib '250' 'e3a15302-b1ec-4bfe-9ac3-3a2cf23d3303' >}} They note, however, that multiple mechanisms can explain this association and that the literature is currently unable to decisively exclude any proposed pathway between climatic change and human conflict.{{< tbib '249' '6013994a-8717-4a99-935a-8a13800fcdc5' >}}
Evidence of the impact of climate on livelihoods is also well established. Barnett and Adger (2003, 2007){{< tbib '191' '0dc9b00c-1fc7-43ee-bcb6-4c8e783e88f1' >}},{{
To frame this chapter, the regional leads wanted to maximize inclusiveness and represent the key sectoral interests of communities and researchers. To select sectors and a full author team, the coordinating lead author and regional chapter lead author distributed an online Google survey from September to October 2016. The survey received 136 responses representing Hawaiʻi and all the U.S.-Affiliated Pacific Islands (USAPI) jurisdictions; respondents identified which of the National Climate Assessment (NCA) sectors they were most interested in learning about with respect to climate change in the Pacific Islands and suggested representative case studies.{{< tbib '223' '884675c9-3e31-483d-b6b9-fd53b99875ae' >}} The five top sectors were picked as the focus of the chapter, and a total of eight lead authors with expertise in those sectors were invited to join the regional team. To solicit additional participation from potential technical contributors across the region, two informational webinars spanning convenient time zones across the Pacific were held; 35 people joined in. The webinars outlined the NCA history and process, as well as past regional reports and ways to participate in this Fourth National Climate Assessment (NCA4).
A critical part of outlining the chapter and gathering literature published since the Third National Climate Assessment (NCA3){{< tbib '224' 'dd5b893d-4462-4bb3-9205-67b532919566' >}} was done by inviting technical experts in the key sectors to participate in a half-day workshop led by each of the lead authors. A larger workshop centered on adaptation best practices was convened with participants from all sectors, as well as regional decision-makers. In all, 75 participants, including some virtual attendees, took part in the sectoral workshops on March 6 and 13, 2017. Finally, to include public concerns and interests, two town hall discussion events on March 6 and April 19, 2017, were held in Honolulu, Hawaiʻi, and Tumon, Guam, respectively. Approximately 100 participants attended the town halls. Throughout the refining of the Key Messages and narrative sections, authors met weekly both via conference call and in person to discuss the chapter and carefully review evidence and findings. Technical contributors were given multiple opportunities to respond to and edit sections. The process was coordinated by the regional chapter lead and coordinating lead authors, as well as the Pacific Islands sustained assessment specialist.
" report_identifier: nca4 statement: 'Climate change impacts in the Pacific Islands are expected to amplify existing risks and lead to compounding economic, environmental, social, and cultural costs (likely, medium confidence). In some locations, climate change impacts on ecological and social systems are projected to result in severe disruptions to livelihoods (likely, high confidence) that increase the risk of human conflict or compel the need for migration. Early interventions, already occurring in some places across the region, can prevent costly and lengthy rebuilding of communities and livelihoods and minimize displacement and relocation (likely, high confidence).
' uncertainties: "A key uncertainty remains the lack of a supporting, detectable anthropogenic signal in the historical data to add further confidence to some regional projections. As such, confidence in the projections is based on agreement among different modeling studies. Additional uncertainty stems from uncertainty in both the projected pattern and magnitude of future sea surface temperatures.{{< tbib '33' '75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1' >}},{{
One study projects an increase in tropical cyclone frequency (TCF) of occurrence around the Hawaiian Islands but stipulates that TCF around the Hawaiian Islands is still very low in a warmed climate, so that a quantitative evaluation of the future change involves significant uncertainties.{{< tbib '40' '9082a92d-e1be-4346-8657-7b172a8f91bc' >}}
Uncertainties in reconstructed global mean sea level (GMSL) change relate to the sparsity of tide gauge records, particularly before the middle of the twentieth century, and to the use of a variety of statistical approaches to estimate GMSL change from these sparse records. Uncertainties in reconstructed GMSL change before the 20th century also relate to the lack of geological proxies (preserved physical characteristics of the past environment that can stand in for direct measurement) for sea level change, the interpretation of these proxies, and the dating of these proxies. Uncertainty in attribution relates to the reconstruction of past changes and the magnitude of natural variability in the climate.
Since NCA3, multiple approaches have been used to generate probabilistic projections of GMSL rise. These approaches are in general agreement. However, emerging results indicate that marine portions of the Antarctic ice sheet are more unstable than previously thought. The rate of ice sheet mass changes remains challenging to project.
In sea level rise projections, Antarctic contributions are amplified along U.S. coastlines, while Greenland contributions are dampened; regional sea level is projected to be higher than if driven by a more extreme Greenland contribution and a somewhat less extreme Antarctic contribution.{{< tbib '17' 'c66bf5a9-a6d7-4043-ad99-db0ae6ae562c' >}}
The degree to which climate variability and change impact conflict, and related causal pathways, remains uncertain. This is compounded by the fact that different types of conflict—social, political, civil, or violent—are conflated.{{< tbib '209' '657d9028-d5b7-4e0c-980e-dd71138c8bd7' >}},{{
Gemenne et al. (2014){{< tbib '208' '32ad430a-4769-4e16-8ece-c28d123504b0' >}} also note that the relationship between climate change and security comes from observation of past patterns and that present and projected climate change have no historical precedent. In effect, understanding past crises and adaptation strategies will no longer be able to help us understand future crises in a time of significant climate change.
The degree to which climate variability and change affect migration decisions made today also remains uncertain. This is in part due to the diverse scenarios that comprise climate migration, which themselves result from multiple drivers of migration.{{< tbib '251' 'b3626f1d-9cfa-469a-b52d-dce3c6a0dff0' >}} Burrows and Kinney (2016){{< tbib '251' 'b3626f1d-9cfa-469a-b52d-dce3c6a0dff0' >}} detail examples of climate extremes leading to migration conflicts since 2000, yet they note that there are surprisingly few case studies on recent climate extremes that lead to migration and conflict specifically, despite an increasing body of literature on the theory.
While researchers disagree as to the degree to which climate change drives conflict and migration and the causal pathways that connect them, there is agreement that further research is needed. Buhaug (2015){{< tbib '252' '9d9049c5-28b9-4029-a6b7-a18838dcdc69' >}} and Gemenne et al. (2014){{< tbib '208' '32ad430a-4769-4e16-8ece-c28d123504b0' >}} argue for research to develop a more refined theoretical understanding of possible indirect and conditional causal connections between climate change and, specifically, violent conflict.{{< tbib '252' '9d9049c5-28b9-4029-a6b7-a18838dcdc69' >}} Hsiang and Burke (2014){{< tbib '250' 'e3a15302-b1ec-4bfe-9ac3-3a2cf23d3303' >}} would like additional research that reduces the number of competing hypotheses that attempt to explain the overwhelming evidence that climatic variables are one of many important causal factors in human conflict.{{< tbib '250' 'e3a15302-b1ec-4bfe-9ac3-3a2cf23d3303' >}} Burrows and Kinney (2016){{< tbib '251' 'b3626f1d-9cfa-469a-b52d-dce3c6a0dff0' >}} explore the potential pathways linking climate change, migration, and increased risk of conflict and argue that future research should focus on other pathways by which climate variability and change are related to conflict, in addition to the climate–migration–conflict pathway. Kallis and Zografos (2014){{< tbib '209' '657d9028-d5b7-4e0c-980e-dd71138c8bd7' >}} seek greater understanding of the potential harm of certain climate change adaptation measures that have the potential to result in maladaptation by spurring conflict.
" uri: /report/nca4/chapter/hawaii-and-pacific-islands/finding/key-message-27-6 url: ~ - chapter_identifier: near-term-adaptation-needs-and-increased-resiliency confidence: 'There is high confidence that the amount of adaptation activity, in particular implementation activity, is increasing. There is less agreement and evidence regarding the consequences of this activity.
' evidence: "There exists extensive documentation in the gray literature of specific adaptation planning and implementation activities underway by local, state, regional, and federal agencies and jurisdictions. The literature also contains reports that attempt to provide an overview of these activities, such as the recent set of case studies in Vogel et. al. (2017).{{< tbib '14' '3c3cc09b-c2d7-4c52-bf8f-c064efa78e93' >}} Websites, such as those of the Georgetown Climate Center (http://www.georgetownclimate.org), provide summaries and examples of adaptation activities in the United States. The sectoral and regional chapters in this National Climate Assessment also provide numerous examples of adaptation planning and implementation activities. The literature also offers work that aims to provide surveys of large numbers of adaptation activity, such as Moser et. al. (2018){{< tbib '121' 'b47b4130-ce3f-4e3e-914d-443a5652abbb' >}} and Stults and Woodruff (2016).{{< tbib '164' '44dd3160-74d0-4173-8ca4-b503fcd93615' >}}
" href: https://data.globalchange.gov/report/nca4/chapter/near-term-adaptation-needs-and-increased-resiliency/finding/key-message-28-1.yaml identifier: key-message-28-1 ordinal: 1 process: 'The scope for this chapter was determined by the Fourth National Climate Assessment (NCA4) Federal Steering Committee, which is made up of representatives from the U.S. Global Change Research Program member agencies. The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3). Authors for this NCA4 chapter were selected to represent a range of public- and private-sector perspectives and experiences relevant to adaptation planning and implementation.
This chapter was developed through technical discussions of relevant evidence and expert deliberation by chapter authors during teleconferences, e-mail exchanges, and a day-long in-person meeting. These discussions were informed by a comprehensive literature review of the evidence base for the current state of adaptation in the United States. The author team obtained input from outside experts in several important areas to supplement its expertise.
' report_identifier: nca4 statement: 'Adaptation planning and implementation activities are occurring across the United States in the public, private, and nonprofit sectors. Since the Third National Climate Assessment, implementation has increased but is not yet commonplace. (High Confidence)
' uncertainties: "While the amount of adaptation-related activity is clearly increasing, the lack of clear standards and the diverse lexicon used in different sectors make it difficult to systematically compare different adaptation activities at the level of outcomes across sectors and regions of the country. In addition, publicly available adaptation plans may never actually result in implementation. It is thus difficult to provide a quantitative assessment of the increase in adaptation activity other than just counting plans and initiatives. Given the reliance on small-sample surveys, judgments about the distribution of adaptation actions across categories have potentially large errors that are difficult to estimate. In addition, it is difficult to assess the contribution of these activities to concrete outcomes such as risk reduction or current and future improvements to well-being, security, and environmental protection.{{< tbib '130' 'dbb9cf98-a2e1-4392-b1f9-38d00259ecdf' >}} There also exists little gap analysis that compares any given set of adaptation activities with what might be appropriate according to some normative standard or what might be reasonably achieved. Thus, while adaptation activities are clearly increasing in the United States, scant evidence exists for judging their consequences.
" uri: /report/nca4/chapter/near-term-adaptation-needs-and-increased-resiliency/finding/key-message-28-1 url: ~ - chapter_identifier: near-term-adaptation-needs-and-increased-resiliency confidence: "There is high confidence that most organizations’ planning is currently based on extensions from the record of local climate conditions.{{< tbib '169' '60233f20-d45f-4086-ada7-00dbd47712c3' >}}
" evidence: "The assumption that the historical record of events and variability will be the same in the future is called the stationarity assumption{{< tbib '27' 'c52f2539-9c5e-4ead-b8b7-f1884c5d662e' >}} and has guided planning for climate and weather events in most places for most of recorded history. The evidence is strong that the stationarity assumption is no longer valid for all impacts and variability in all locations, because climate change is altering both the events and their variability.{{< tbib '3' '666daffe-2c3b-4e2d-9157-16b989860618' >}},{{
The scope for this chapter was determined by the Fourth National Climate Assessment (NCA4) Federal Steering Committee, which is made up of representatives from the U.S. Global Change Research Program member agencies. The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3). Authors for this NCA4 chapter were selected to represent a range of public- and private-sector perspectives and experiences relevant to adaptation planning and implementation.
This chapter was developed through technical discussions of relevant evidence and expert deliberation by chapter authors during teleconferences, e-mail exchanges, and a day-long in-person meeting. These discussions were informed by a comprehensive literature review of the evidence base for the current state of adaptation in the United States. The author team obtained input from outside experts in several important areas to supplement its expertise.
' report_identifier: nca4 statement: 'Successful adaptation has been hindered by the assumption that climate conditions are and will be similar to those in the past. Incorporating information on current and future climate conditions into design guidelines, standards, policies, and practices would reduce risk and adverse impacts. (High Confidence)
' uncertainties: "While significant uncertainties can exist in estimating the extent to which current variability differs from historic observations in any particular location, there is robust evidence that such differences do occur in many locations (see Ch. 18: Northeast; Ch. 19: Southeast; Ch. 20: U.S. Caribbean; Ch. 21: Midwest; Ch. 22: N. Great Plains; Ch. 23: S. Great Plains; Ch. 24: Northwest; Ch. 25: Southwest; Ch. 26: Alaska; and Ch. 27: Hawaiʻi & Pacific Islands).{{< tbib '5' '29960c69-6168-4fb0-9af0-d50bdd91acd3' >}},{{
Significant agreement and strong evidence provide high confidence that adaptation is a form of iterative risk management and that this is an appropriate framework for understanding, addressing, and communicating climate-related risks.{{< tbib '33' '7f8b90be-c5d1-43b5-8b7f-a485ef08c7ec' >}}
" evidence: "Evidence from a large body of literature and observations of experience support the judgment that iterative risk management is a useful framework (e.g., National Research Council 2009, America's Climate Choices 2010, Kunreuther et al. 2012{{< tbib '142' '7ab8b14a-38c7-4128-b0e3-fe1ab65edac0' >}},{{
The scope for this chapter was determined by the Fourth National Climate Assessment (NCA4) Federal Steering Committee, which is made up of representatives from the U.S. Global Change Research Program member agencies. The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3). Authors for this NCA4 chapter were selected to represent a range of public- and private-sector perspectives and experiences relevant to adaptation planning and implementation.
This chapter was developed through technical discussions of relevant evidence and expert deliberation by chapter authors during teleconferences, e-mail exchanges, and a day-long in-person meeting. These discussions were informed by a comprehensive literature review of the evidence base for the current state of adaptation in the United States. The author team obtained input from outside experts in several important areas to supplement its expertise.
' report_identifier: nca4 statement: 'Adaptation entails a continuing risk management process; it does not have an end point. With this approach, individuals and organizations of all types assess risks and vulnerabilities from climate and other drivers of change (such as economic, environmental, and societal), take actions to reduce those risks, and learn over time. (High Confidence)
' uncertainties: 'The literature and practice of climate change are undergoing a process of maturation and convergence. The process began with many organizations and sectors developing their own approaches and terminology in response to climate risks, meaning that a wide variety of approaches still exist in the field. We believe that the field will progress and converge on the most effective approaches, including iterative risk management. But this convergence is still in process, and the outcome remains uncertain.
' uri: /report/nca4/chapter/near-term-adaptation-needs-and-increased-resiliency/finding/key-message-28-3 url: ~ - chapter_identifier: near-term-adaptation-needs-and-increased-resiliency confidence: 'There is suggestive evidence that provides medium confidence that many proactive adaptation actions offer significant benefits that exceed their costs. However, because of a small sample size and insufficient evaluation, it is in general hard to know the extent to which this is true in any particular case. There is strong agreement that evaluating adaptation involves consideration of a wide range of measures of social well-being.
' evidence: "Both limited field applications and literature reviews highlight adaptation co-benefits, including those associated with equity considerations.{{< tbib '83' '971185c1-a31f-4c15-8454-57f273b4ed33' >}} Near-term benefits are assessed from observations of adaptation results, as well as from comparisons to similar situations without such responses; longer-term benefits are generally assessed from projections.
" href: https://data.globalchange.gov/report/nca4/chapter/near-term-adaptation-needs-and-increased-resiliency/finding/key-message-28-4.yaml identifier: key-message-28-4 ordinal: 4 process: 'The scope for this chapter was determined by the Fourth National Climate Assessment (NCA4) Federal Steering Committee, which is made up of representatives from the U.S. Global Change Research Program member agencies. The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3). Authors for this NCA4 chapter were selected to represent a range of public- and private-sector perspectives and experiences relevant to adaptation planning and implementation.
This chapter was developed through technical discussions of relevant evidence and expert deliberation by chapter authors during teleconferences, e-mail exchanges, and a day-long in-person meeting. These discussions were informed by a comprehensive literature review of the evidence base for the current state of adaptation in the United States. The author team obtained input from outside experts in several important areas to supplement its expertise.
' report_identifier: nca4 statement: 'Proactive adaptation initiatives—including changes to policies, business operations, capital investments, and other steps—yield benefits in excess of their costs in the near term, as well as over the long term (medium confidence). Evaluating adaptation strategies involves consideration of equity, justice, cultural heritage, the environment, health, and national security (high confidence).
' uncertainties: 'Benefits are based on understanding the relevant systems so that one can compare similar cases and construct counterfactuals. Such understanding is excellent for many engineered systems (for example, how a storm drain performs under various rainfall scenarios) but is less robust for many biological systems. Benefit–cost ratios can have large uncertainties associated with estimates of costs, the projection of benefits, and the economic valuation of benefits. In addition, because expected differences in benefit–cost ratios are sufficiently large and the number of current examples is sufficiently low, there are large uncertainties in applying results from one case to another.
' uri: /report/nca4/chapter/near-term-adaptation-needs-and-increased-resiliency/finding/key-message-28-4 url: ~ - chapter_identifier: near-term-adaptation-needs-and-increased-resiliency confidence: 'There is significant agreement that provides high confidence, in at least some cases, that both 1) mainstreaming climate information into existing risk management and 2) creating enabling environments and institutions to improve adaptation capacity, implementation, and evaluation reduce risk, produce co-benefits across communities and sectors, and help secure economic investments into the future.
' evidence: "There is significant agreement, but only case study evidence, that effective adaptation can be realized by mainstreaming.{{< tbib '100' '40cd1072-ac17-4dfa-ba98-a554bf1a0458' >}},{{
The scope for this chapter was determined by the Fourth National Climate Assessment (NCA4) Federal Steering Committee, which is made up of representatives from the U.S. Global Change Research Program member agencies. The scope was also informed by research needs identified in the Third National Climate Assessment (NCA3). Authors for this NCA4 chapter were selected to represent a range of public- and private-sector perspectives and experiences relevant to adaptation planning and implementation.
This chapter was developed through technical discussions of relevant evidence and expert deliberation by chapter authors during teleconferences, e-mail exchanges, and a day-long in-person meeting. These discussions were informed by a comprehensive literature review of the evidence base for the current state of adaptation in the United States. The author team obtained input from outside experts in several important areas to supplement its expertise.
' report_identifier: nca4 statement: 'Integrating climate considerations into existing organizational and sectoral policies and practices provides adaptation benefits. Further reduction of the risks from climate change can be achieved by new approaches that create conditions for altering regulatory and policy environments, cultural and community resources, economic and financial systems, technology applications, and ecosystems. (High Confidence)
' uncertainties: 'It is not well understood how community acceptance of needed adaptations develops. This presents both a barrier to the implementation of adaptation measures and an opportunity for additional research into ways to close this gap in understanding. Additionally, a need exists to clarify the co-benefits of addressing multiple threats and opportunities. Effective adaptation also depends on networks of collaboration among researchers and practitioners and the long-term support of monitoring networks. The sustainability of both types of networks is a major uncertainty. Their effectiveness is both an uncertainty and major research need.
' uri: /report/nca4/chapter/near-term-adaptation-needs-and-increased-resiliency/finding/key-message-28-5 url: ~