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' >}},{{