finding 11.4 : key-message-11-4

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).



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:

Multiple review studies have documented that cities in all parts of the United States are undertaking adaptation and mitigation actions.60233f20-d45f-4086-ada7-00dbd47712c3,e092ae8f-d7ed-4879-8773-ea442b9fd12d,c649aa60-e3b5-47a4-8a40-0d7ef5cf98d8 Municipal departments, including public works, water systems, and transportation, along with public, private, and civic actors, work to assess vulnerability and reduce risk. Actions include land-use planning, protecting critical infrastructure and ecosystems, installing green infrastructure, and improving emergency preparedness and response.60233f20-d45f-4086-ada7-00dbd47712c3,98a171ed-c572-4c28-a49b-03110f1cac10,e092ae8f-d7ed-4879-8773-ea442b9fd12d,0f9545b2-e0ff-42fb-a5df-7237a2e9d494,e40c4470-2588-4c8c-8fbe-b95317579882 Many cities are part of multicity networks (for example, the Great Lakes Climate Adaptation Network, ICLEI, and C40 Cities Climate Leadership Group) that provide opportunities for peer-to-peer learning, sharing best practices, and technical assistance.3c3cc09b-c2d7-4c52-bf8f-c064efa78e93,98a171ed-c572-4c28-a49b-03110f1cac10,0f9545b2-e0ff-42fb-a5df-7237a2e9d494,9681bb6b-eda0-4d8b-8034-e7104987c644 Researchers have recognized the benefits of shared motivation and resource pooling across cities3c3cc09b-c2d7-4c52-bf8f-c064efa78e93 and of incorporating local knowledge, priorities, and values into adaptation planning.60233f20-d45f-4086-ada7-00dbd47712c3,b0952748-e532-4d7c-ace8-66786863734d The private sector, utilities, nongovernmental organizations, libraries, museums, and civic organizations are involved with urban adaptation and mitigation.b75bf8c7-f76f-4fd9-98d4-fd8fa08341f2,60233f20-d45f-4086-ada7-00dbd47712c3,3c3cc09b-c2d7-4c52-bf8f-c064efa78e93,e092ae8f-d7ed-4879-8773-ea442b9fd12d,bc596c87-23de-4edf-9351-ff2fe74ba4c7,7d48a881-5644-4b8f-977e-be1a59f45da3,67a4eb83-205a-49a9-95c8-32acdb53b6f5 Studies are beginning to analyze the social, economic, and political factors that shape whether and how cities carry out climate change response.98a171ed-c572-4c28-a49b-03110f1cac10,e092ae8f-d7ed-4879-8773-ea442b9fd12d,4ed849f3-a967-4d18-840e-4441a79de3f6,1cb45663-ad95-44da-8a33-6afefb926301,95f74b48-a288-42e6-865e-6d39b6463493

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 risk133d9f9c-e1fd-4c50-b349-67eef6048291,9ec5956c-c78a-4fef-86be-4fed318bf303,e904b5f2-2c5e-4e55-8365-2ba748291939,8b1d0928-f216-4d11-8a06-b710ff7f2eae,d3a3ca44-1e49-41ee-9063-dc1be22dec3c,66133278-2088-4180-bea3-d55202d3bd76 and flooding impacts.993dacc4-2fe3-4fdb-a822-70538be4da25,21e7c6db-f283-46b0-ac33-60ee4d5d837b,917f65f2-6868-4f60-b499-c8560716f5fc These actions can provide additional public health and economic benefits.3c3cc09b-c2d7-4c52-bf8f-c064efa78e93,50b8efeb-5360-49ff-be40-27718834a378,851f8d77-bb6b-439a-b252-441831cebda2,b17b3711-69f8-4b4e-853b-9264efb971f1,6177fcba-e6ac-48c8-aed7-ef5eed7b1b9c Studies have also noted that low-regret and incremental urban adaptation are not likely to significantly reduce the impacts of projected climate change.3c3cc09b-c2d7-4c52-bf8f-c064efa78e93,1cb45663-ad95-44da-8a33-6afefb926301,9dbe259c-7b0d-4bbb-b0bc-2e24cc3d106f In addition, several studies discuss how urban adaptation can cause adverse consequences related to existing socioeconomic and spatial inequalities and the uneven distribution of urban climate risks.8a4248ca-3d8c-4bdb-a28d-292a149733ba,3a068e5f-0c2e-4a23-b533-1fc512482ab3,87cfc4e1-f44b-4fb0-ae65-cbeec57ebfac,91fcdcf9-a731-4ab0-9f46-3eb4ac0eb53d

New information and remaining 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.e092ae8f-d7ed-4879-8773-ea442b9fd12d,c649aa60-e3b5-47a4-8a40-0d7ef5cf98d8 Much of this uncertainty arises from the difficulties inherent in predicting the future impacts of climate change. This uncertainty is compounded by a lack of regional and local data for many cities, by the difficulty of evaluating the effects of climate change on local extremes,3e9b6eba-21a7-474e-9773-190a0ec18257,66133278-2088-4180-bea3-d55202d3bd76 and by the inability of knowing how climate changes intersect with other urban changes.cb667add-afc5-472b-a8bc-6c688712b9c8,8be634e3-a62f-44d2-9cde-dd7010cdad04 Moreover, there is a lack of forward-looking models and standardized monitoring strategies to test the costs, co-benefits, and effectiveness of urban response. Adaptation actions that focus solely on physical protection of urban assets are not likely to effectively address social vulnerability.98a171ed-c572-4c28-a49b-03110f1cac10,3a068e5f-0c2e-4a23-b533-1fc512482ab3 Urban adaptation effectiveness depends heavily on local characteristics. While cities do learn best practices through multicity networks, one city’s strategy may not be as applicable to other cities.

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.98a171ed-c572-4c28-a49b-03110f1cac10,4ed849f3-a967-4d18-840e-4441a79de3f6,95f74b48-a288-42e6-865e-6d39b6463493 Although cities are leading the way in adaptation and mitigation, many face significant barriers such as resource challenges, which will affect the rate of spread, extent, and duration of urban response.60233f20-d45f-4086-ada7-00dbd47712c3,f1f67e52-3ceb-47c9-8961-a6640d15a618 There is little research on the effectiveness of different incentives for urban response or how to best support action in low-income communities.

Assessment of confidence based on evidence:

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.

References :

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