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' >}},{{