finding 17.1 : sea-level-rise-threatens-environment

Sea level rise poses widespread and continuing threats to both natural and built environments and to the regional economy.

This finding is from chapter 17 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the process was the Southeast Regional Climate Assessment Workshop that was held on September 26-27, 2011, in Atlanta, with approximately 75 attendees. This workshop began the process leading to a foundational Technical Input Report (TIR). That 344-page foundational “Southeast Region Technical Report to the National Climate Assessment”4739fda9-9431-4cb3-8572-5f992fd61519 comprised 14 chapters from over 100 authors, including all levels of government, non-governmental organizations, and business. The writing team held a 2-day meeting in April 2012 in Ft. Lauderdale, engaged in multiple teleconference and webinar technical discussions, which included careful review of the foundational TIR,4739fda9-9431-4cb3-8572-5f992fd61519 nearly 60 additional technical inputs provided by the public, and other published literature and professional judgment. Discussions were followed by expert deliberation of draft key messages by the authors, and targeted consultation with additional experts by the Southeast chapter writing team and lead author of each key message.

Description of evidence base: The key message and supporting text summarize extensive evidence documented in the Southeast Technical Input Report.4739fda9-9431-4cb3-8572-5f992fd61519 A total of 57 technical inputs on a wide range of southeast-relevant topics (including sea level rise) were also received and reviewed as part of the Federal Register Notice solicitation for public input. Evidence that the rate of sea level rise has increased is based on satellite altimetry data and direct measurements such as tide gauges (Ch. 2: Our Changing Climate, Key Message 10). Numerous peer-reviewed publications describe increasing hazards associated with sea level rise and storm surge, heat waves, and intense precipitation for the Southeast.4739fda9-9431-4cb3-8572-5f992fd61519 For sea level rise, the authors relied on the NCA Sea Level Change Scenariod8089822-678e-4834-a1ec-0dca1da35314 and detailed discussion in the foundational TIR.4739fda9-9431-4cb3-8572-5f992fd61519 Evidence that sea level rise is a threat to natural and human environments is documented in detail within the foundational TIR4739fda9-9431-4cb3-8572-5f992fd61519 and other technical inputs, as well as considerable peer-reviewed literature (for example, Campanella 2010).9f212258-2749-4523-8d0c-2ba849f7ed25 Field studies document examples of areas that are being flooded more regularly, saltwater intrusion into fresh water wells,c95237bc-7d04-4c92-bb83-4a9d8ac3eaed and changes from fresh to saltwater in coastal ecosystems (for example, freshwater marshes) causing them to die,7ec245d4-187a-493b-9262-d2e89b5c29c4 and increases in vulnerability of many communities to coastal erosion. Economic impacts are seen in the cost to avoid flooded roads, buildings, and ports;77b7f3d9-979b-49e1-939d-adc188ca4436 the need to drill new fresh water wells;c95237bc-7d04-4c92-bb83-4a9d8ac3eaed and the loss of coastal ecosystems and their storm surge protection.

New information and remaining uncertainties: Tremendous improvement has been made since the last Intergovernmental Panel on Climate Change evaluation of sea level rise in 2007,c54b9473-cdc3-4f22-97a8-4df5253f9682 with strong evidence of mass loss of Greenland icecap and glaciers worldwide (Ch. 2: Our Changing Climate). Improved analyses of tide gauges, coastal elevations, and circulation changes in offshore waters have also provided new information on accelerating rates of rise (Ch. 2: Our Changing Climate, Figure 2.26). These have been documented in the NCA Sea Level Change Scenario publication.d8089822-678e-4834-a1ec-0dca1da35314 Uncertainties in the rate of sea level rise through this century stems from a combination of large differences in projections among different climate models, natural climate variability, uncertainties in the melting of land-based glaciers and the Antarctic and Greenland ice sheets especially, and uncertainties about future rates of fossil fuel emissions. A further key uncertainty is the rate of vertical land movement at specific locations. The two factors – sea level rise and subsidence – when combined, increase the impact of global sea level rise in any specific area. A third area of uncertainty is where and what adaptive plans and actions are being undertaken to avoid flooding and associated impacts on people, communities, facilities, infrastructure, and ecosystems.

Assessment of confidence based on evidence: Sea level is expected to continue to rise for several centuries, even if greenhouse gas emissions are stabilized, due to the time it takes for the ocean to absorb heat energy from the atmosphere. Because sea levels determine the locations of human activities and ecosystems along the coasts, increases in sea level and in the rate of rise will nearly certainly have substantial impacts on natural and human systems along the coastal area. What specific locations will be impacted under what specific levels of sea level rise needs to be determined location-by-location. However, given that many locations are already being affected by rising seas, more and more locations will be impacted as sea levels continue to rise. Confidence in this key message is therefore judged to be very high.

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