Nationally important assets, such as ports, tourism and fishing sites, in already-vulnerable coastal locations, are increasingly exposed to sea level rise and related hazards. This threatens to disrupt economic activity within coastal areas and the regions they serve and results in significant costs from protecting or moving these assets.

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, as well as the extant scientific literature. The evidence base for increased exposure to assets is strong. Many publications have assessed at-risk areas (for example, Biging et al. 2012; Cooley et al. 2012; Heberger et al. 2009; Neumann et al. 2010aca601d1d-e05f-4c7c-b5ab-7f35cd27ad57 0fece8dd-1233-4ec3-8958-2944a5b3c967 2ef35c42-765f-407e-b517-11db86a11c70 c7d9400d-b597-4a6f-bd6e-6ad907669146). Highly reliable economic activity information is available from recurring surveys conducted by the National Oceanographic and Atmospheric Administration (NOAA) and others, and asset exposure is conclusively demonstrated by historical information (from storm and erosion damage), elevation data (in Geographic Information System (GIS)-based, LIDAR, and other forms), and numerous vulnerability and adaptation studies of the built environment. Further evidence is provided in technical input reports and other NCA chapters on infrastructure and urban systems (Ch. 11: Urban),f0803451-5a89-474a-974f-99c13fdc725d transportation (Ch. 5: Transportation),6b4d3283-49dc-4b8d-830b-aa554e37279f and energy (Ch. 4: Energy). A number of studies in addition to the ones cited in the text, using various economic assumptions, aim to assess the cost of protecting or relocating coastal assets and services. Many publications and reports explore the cost of replacing services offered by ports,6b4d3283-49dc-4b8d-830b-aa554e37279f 6ef87983-391a-497e-88d7-0e9ad38c215d though one study3f1fc729-ccd6-48f0-9062-5bc999cc068e notes that few ports are implementing adaptation practices to date. The economic consequences of climate change on tourism are supported by a number of recent studies.88c9a12d-64ab-4f45-ad5c-58196f9e824f da18c6c7-f8e5-4783-8d85-678cbc3ed429 109eb10a-7b33-4fb9-93d6-6d483fc330b7 6ef87983-391a-497e-88d7-0e9ad38c215d 6fd7abfe-17d7-49a9-bc90-bf85fa4041d3 The threats of climate change on fishing have been explored in the coastal zone technical input report.c9647af9-db7f-4f6a-89bd-2f2293ad26e5 Additional evidence comes from empirical observation: public statements by private sector representatives and public officials indicate high awareness of economic asset exposure and a determination to see those assets protected against an encroaching sea, even at high cost (New York City, Miami Dade County, San Francisco airport, etc.). The economic value of exposed assets and activities is frequently invoked when they get damaged or interrupted during storm events (for example, Hallegattee 2012b8396a7f-859b-47be-adcb-16af1eae2dde). Threats to economic activity are also consistently cited as important to local decision-making in the coastal context (for example, Titus et al. 2009ca5b5626-5013-41d6-8815-913abda50bf7).

New information and remaining uncertainties: The projected rate of sea level rise is fully accounted for through the use of common scenarios. We note, however, that there is currently limited impacts literature that uses the lowest or highest scenario for 2100, and no studies that specifically use the broader range of SLR (0.7 to 6.6 feet,) and NCA land-use scenarios (60% to 164% increase in urban and suburban land area).05a757a8-7972-4f33-aed8-424b0afb8fc4 The projected severity and frequency of storm damage in any given location cannot yet be fully accounted for due to uncertainties in projecting future extratropical and tropical storm frequency, intensity, and changes in storm tracks for different regions.c9647af9-db7f-4f6a-89bd-2f2293ad26e5 The timely implementation and efficacy of adaptation measures, including planned retreat, in mitigating damages are accounted for in the underlying literature (for example, by varying assumptions about the timing of implementation of adaptation measures, the type of adaptation measures, and other economic assumptions such as discount rates). However, such studies can only test the sensitivity of conclusions to these assumptions; they do not allow statements about what is occurring on the ground. Well-established post-hoc assessments96dc08d0-5be0-4d8d-b839-acac057dfd5b suggest that hazard mitigation action is highly cost-effective (for every dollar spent, four dollars in damages are avoided). A more recent study suggests an even greater cost-effectiveness.2ef35c42-765f-407e-b517-11db86a11c70

Assessment of confidence based on evidence: Given the evidence base, the well-established accumulation of economic assets and activities in coastal areas, and the directional trend of sea level rise, we have very high confidence in the main conclusion that resources and assets that are nationally important to economic productivity are threatened by SLR and climate change. While there is currently no indication that the highest-value assets and economic activities are being abandoned in the face of sea level rise and storm impacts, we have very high confidence that the cost of protecting these assets in place will be high, and that the cost will be higher the faster sea level rises relative to land. We have very high confidence that adequate planning and arrangement for future financing mechanisms, timely implementation of hazard mitigation measures, and effective disaster response will keep the economic impacts and adaptation costs lower than if these actions are not taken. We are not able to assess timing or total cost of protecting or relocating economic assets with any confidence at this time, due to uncertainties in asset-specific elevation above sea level, in the presence and efficacy of protective measures (at present and in the future), in the feasibility of relocation in any particular case, and uncertainties in future storm surge heights and storm frequencies.

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