Socioeconomic disparities create uneven exposures and sensitivities to growing coastal risks and limit adaptation options for some coastal communities, resulting in the displacement of the most vulnerable people from coastal areas.

This finding is from chapter 25 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the assessment process was a Chapter Lead Authors meeting held in St. Louis, Missouri in April 2012. The key messages were initially developed at this meeting. Key vulnerabilities were operationally defined as those challenges that can fundamentally undermine the functioning of human and natural coastal systems. They arise when these systems are highly exposed and sensitive to climate change and (given present or potential future adaptive capacities) insufficiently prepared or able to respond. The vulnerabilities that the team decided to focus on were informed by ongoing interactions of the author team with coastal managers, planners, and stakeholders, as well as a review of the existing literature. In addition, the author team conducted a thorough review of the technical input reports (TIR) and associated literature, including the coastal zone foundational TIR prepared for the National Climate Assessment (NCA).c9647af9-db7f-4f6a-89bd-2f2293ad26e5 Chapter development was supported by numerous chapter author technical discussions via teleconference from April to June 2012.

Description of evidence base: The key message and supporting text summarize extensive evidence documented in the coastal zone technical input report.c9647af9-db7f-4f6a-89bd-2f2293ad26e5 Technical input reports (68) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input, along with the extant literature. Evidence base is moderate: assessment of the social vulnerability to coastal impacts of climate change is a comparatively new research focus in the United States, and clearly an advance since the prior NCA.e251f590-177e-4ba6-8ed1-6f68b5e54c8a There are currently multiple published, peer-reviewed studies, by different author teams, using different vulnerability metrics, which all reach the same conclusion: economically and socially vulnerable individuals and communities face significant coastal risks and have a lower adaptive capacity than less socially vulnerable populations. Studies have shown that the U.S. coastal population is growing c5b5b0ad-2a2e-45da-868f-54313282590a 85f2d3eb-131c-4622-8d3f-fd6c1abe2f9c and have assessed the importance of this population for climate change exposure.97387e44-8bfc-413a-948c-e6dc67f5e7cd ea43448c-4127-4757-8447-b71e95f65fce ed5a3cbf-175f-47f5-91f8-2d6225e18b3e The social factors that play key roles in coastal vulnerability are detailed in numerous publications.c7d9400d-b597-4a6f-bd6e-6ad907669146 7e30a623-2378-40b0-8295-729d582193ec 796c4617-7dcd-433e-bb0e-805cdab4c136 2f7da448-3778-4a00-ada5-e71c63dee873 808ba10c-7b2e-4d68-910f-0a00c168c503 a02c9e99-df7c-4f4b-8345-74c470d39b16 There is an additional body of evidence emerging in the literature that also supports this key message, namely the growing literature on “barriers to adaptation,” particularly from studies conducted here in the United States.c9647af9-db7f-4f6a-89bd-2f2293ad26e5 c7d9400d-b597-4a6f-bd6e-6ad907669146 822df4d2-3a7d-450b-9924-5543158d5d08 8472db31-6ff4-47f2-8842-4173dcd58e4e e631bb4f-7e97-4596-9ad5-8b6cacf4f29b c1e86158-f0cf-4b7d-bc99-02fe2630e8af This literature reports on the limitations poorer communities face at present in beginning adaptation planning, and on the challenges virtually all communities face in prioritizing adaptation and moving from planning to implementation of adaptation options. There is empirical evidence for how difficult it is for small, less wealthy communities (for example, the Native communities in Alaska or southern Louisiana) to obtain federal funds to relocate from eroding shorelines.70dfc033-956a-400a-bc71-86379a7b7350 42269c56-1785-48ec-a81b-6eeb784de417 Eligibility criteria (positive benefit-cost ratios) make it particularly difficult for low-income communities to obtain such funds; current federal budget constraints limit the available resources to support managed retreat and relocation.3268bd48-c8c0-4c28-afdb-281d35319c1d ea960d1b-926b-4751-8608-4c8d62ec5522 The recent economic hardship has placed constraints even on the richer coastal communities in the U.S. in developing and implementing adaptation strategies, for example in California.e631bb4f-7e97-4596-9ad5-8b6cacf4f29b While the economic situation, funding priorities, or institutional mechanisms to provide support to socially vulnerable communities will not remain static over time, there is no reliable scientific evidence for how these factors may change in the future.

New information and remaining uncertainties: The body of research on this topic is largely new since the prior NCA in 2009.e251f590-177e-4ba6-8ed1-6f68b5e54c8a Each of the peer-reviewed studies discusses data gaps and methodological limitations, as well as the particular challenge of projecting demographic variables – a notoriously difficult undertaking – forward in time. While methods for population projections are well established (typically using housing projections), those, in turn, depend on more difficult to make assumptions about fertility, migration, household size, and travel times to urban areas. The conclusion is limited by uneven coverage of in-depth vulnerability studies; although those that do exist are consistent with and confirm the conclusions of a national study.8b9be5aa-a391-4ed6-a26e-20959b4417ac This latter study was extended by applying the same approach, data sources, and methodology to regions previously not covered, thus closing important informational gaps (Hawai‘i, Alaska, the Great Lakes region). Data gaps remain for most coastal locations in the Pacific Islands, Puerto Rico, and other U.S. territories. The most important limit on understanding is the current inability to project social vulnerability forward in time. While some social variables are more easily predicted (for example, age and gender distribution) than others (for example, income distribution, ethnic composition, and linguistic abilities), the predictive capability declines the further out projections aim (beyond 2030 or 2050). Further, it is particularly difficult to project these variables in specific places subject to coastal risks, as populations are mobile over time, and no existing model reliably predicts place-based demographics at the scale important to these analyses.

Assessment of confidence based on evidence: We have high confidence in this conclusion, as it is based on well-accepted techniques, replicated in several place-based case studies, and on a nationwide analysis, using reliable Census data. Consistency in insights and conclusions in these studies, and in others across regions, sectors, and nations, add to the confidence. The conclusion does involve significant projection uncertainties, however, concerning where socially vulnerable populations will be located several decades from now. Sensitivity analysis of this factor, and overall a wider research base is needed, before a higher confidence assessment can be assigned.

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