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).

This finding is from chapter 11 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

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.

Description of evidence base:

Urban areas provide resources and opportunities for residents’ quality of life.f1f67e52-3ceb-47c9-8961-a6640d15a618^,5d6b00dd-dfee-4b0a-a11a-ab6ec4a6724d However, many cities face challenges to prosperity, including aging and deteriorating infrastructure,9115ee8c-84a2-43a3-96dc-09b6fcacc03f social inequalities,d505cee1-e247-4ebc-a51a-88209666d77f^,0d9c1352-071a-4794-a468-8e01bf0876f1 and lack of economic growth.ce92fa43-b6a4-4f47-8a54-8d5d85212ab1^,f7997d62-0d50-4ba1-b304-ff11b5d73e72 These challenges play out differently depending on a city’s geographic location, economic history, urban development pattern, and governance. Studies link urban development with lower air,1536895c-080f-4958-9984-8200a89467a3 water,e7721b15-f7cb-4a65-a886-0268ab0fb699 and soilc9635569-e7c7-4820-b287-d12db9529476 quality; altered microclimates (for example, urban heat islands);10ee76ca-2db3-429c-baf1-2ff5d1043407^,3e9b6eba-21a7-474e-9773-190a0ec18257 increased risk of certain vector-borne diseases;87664884-f938-4d71-82a3-e918a98673e2 and adverse effects on biodiversity and ecosystem functioning.ff1fea07-c899-4e5f-aff2-76510d06c57b^,bc3ad363-5a7c-4b6a-9ab9-c8f3477f416c^,7c940ebf-7e86-4421-b752-44af87504e32 Exposure to temperature extremes,1aca1900-c64c-4624-a696-3aab59ba6673 allergens,9f17954f-4786-482f-a8c9-1895709bd7a8 and toxic substancesd6397bc1-e245-41fa-9e42-6f1744e59282 and limited access to healthy foodc9bda474-d322-478c-8574-21d8dc7a4f5c^,e767c1c1-94e1-4fd0-ba15-b350acefa691^,68f6abb6-10f5-4d3d-9201-e11a1aecc5c9 and green spaceea8728bd-b961-4115-98d9-f834d50568ab^,b4bad932-3201-4c5e-b52f-22556f558f85^,2aea16d3-6fcf-4d8a-8de8-fe4b316de0b4 create environmental and social vulnerabilities for urban populations. Vulnerabilities are distributed unevenly within cities and reflect social inequalities related to differences in race, class, ethnicity, gender, health, and disability.5a79e12b-b65c-40ef-8f80-7bcb04d57a1d These populations of concern are at a greater risk of exposure to climate change and its impacts.^{ce2db20d-ff1b-407c-873e-fde134a7929c,0d9c1352-071a-4794-a468-8e01bf0876f1,3a068e5f-0c2e-4a23-b533-1fc512482ab3}

Climate change combines with other trends to increase stress on the health and well-being of urban residents.c9bda474-d322-478c-8574-21d8dc7a4f5c^,0d9c1352-071a-4794-a468-8e01bf0876f1^,1aca1900-c64c-4624-a696-3aab59ba6673^,e767c1c1-94e1-4fd0-ba15-b350acefa691 Research demonstrates that climate change can exacerbate many of the vulnerabilities described above. It raises temperatures, alters weather patterns, and increases the frequency and severity of extreme weather events, creating risks to urban ecosystems (such as urban tree cover),bcf8379c-fedb-443a-a971-16fe922a3a27^,477c6e61-7962-4e01-9feb-e6f0f41f0d7e^,e25ea9e7-07f8-4104-9ea0-b0d48ae82ee1 infrastructure both above and below grade,bf972224-c8ca-4c0b-82f0-ebb735ba04ce^,a72701dd-9c86-40c3-bf56-5b75c25f4d0f^,e3ac668b-0cd6-40c6-afb5-2df1600ca96c historic and cultural sites,83f70578-19a7-4a1c-a2af-92f1c28f5740^,a9d3f75d-31a9-4b7b-b986-df4d46945cd5^,e25ea9e7-07f8-4104-9ea0-b0d48ae82ee1^,f41903c4-bc50-4c95-a0c0-54aaf4c51ad7^,54a0cbcb-449e-4a93-b84d-5a135504dc2d^,c83c98ff-ea0e-47c9-9e83-55261c8ca24f and residents’ physical and mental health.f360379a-fb12-46a0-aef4-a04ce55ddbed^,97e24319-c8e0-4103-a191-7b8a4047297a^,d72623f9-1bb8-4f30-b89e-c5322edab9ff^,349d443c-b692-4b9d-8b1b-a22887a292a7 Coupled with climate change, urban expansion increases the risk of infectious diseasec8a2bcc1-87dc-4937-97fd-557f09dd82a0^,a031b362-5967-4b59-8b70-c09a4355716f and air quality problems from wildfires.95598d88-7aeb-43df-9e75-22aaed95747b^,7ef4f167-6123-4660-8d23-e50f7fa99dbc

Metropolitan areas often have more resources than rural ones, as reflected in income per capita, employment rates, and workforce education.96fca595-cfc0-4364-b138-51bd2cceb1b3^,6b1c3841-ec69-422b-904f-3bf05bff06e1 Innovative urban problem solving that builds on these resources can take the form of policies and institutional collaborations,c1323a14-9ac9-4070-a83f-91dd1dea9cb1^,ba5cb012-f7fc-420f-924c-be2c0276aa86 technologies,f1f67e52-3ceb-47c9-8961-a6640d15a618^,79161ff1-6099-4c09-a5a6-e0a5a8b0c441 eco- and nature-based solutions,16fc0eef-5efa-4b07-bdad-0d60d7b48af6^,3ea90c21-a2ee-4ca3-8b36-0e2296641ee5 public–private partnerships,3c3cc09b-c2d7-4c52-bf8f-c064efa78e93 social network and climate justice initiatives,8a4248ca-3d8c-4bdb-a28d-292a149733ba^,65e94984-6669-49e8-a41e-aff0cbdae813 “smart” cities,57e3e16c-6b52-436a-ab26-3a19947f8dff^,f1f67e52-3ceb-47c9-8961-a6640d15a618^,79161ff1-6099-4c09-a5a6-e0a5a8b0c441 or a combination of approaches. However, cities vary greatly in their capacity to innovate for reasons related to size, staffing, and existing resources.

New information and remaining 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.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,f1f67e52-3ceb-47c9-8961-a6640d15a618 which are projected with far less certainty than incremental changes in average conditions.31bf15ab-c374-4466-8b4c-894a527813cb Moreover, projections are not often made at the city scale.8be634e3-a62f-44d2-9cde-dd7010cdad04 Climate change may accelerate urban tree growth, but overall effects on growing conditions depend on a variety of factors.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.5b7e5de3-722a-4010-8d86-44e9722e3da9

Urban climate vulnerability depends on local social, political, demographic, environmental, and economic characteristics.3c3cc09b-c2d7-4c52-bf8f-c064efa78e93^,15c8ad4d-f96a-4bfb-8944-63d220e42f3b^,f1f67e52-3ceb-47c9-8961-a6640d15a618 Urban exposure to climate change depends on geographic factors (such as latitude, elevation, hydrology, distance from the coast).f1f67e52-3ceb-47c9-8961-a6640d15a618 Some places may be able to protect quality of life from minor climate stresses but not from extreme, though rare, events.f1f67e52-3ceb-47c9-8961-a6640d15a618 The speed and pace of innovative problem solving is difficult to predict, as is its effect on quality of life^..3c3cc09b-c2d7-4c52-bf8f-c064efa78e93

Assessment of confidence based on evidence:

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).