Flooding and erosion in coastal areas are already occurring even at existing sea levels and damaging some California coastal areas during storms and extreme high tides. Sea level rise is projected to increase as Earth continues to warm, resulting in major damage as wind-driven waves ride upon higher seas and reach farther inland.

This finding is from chapter 20 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 the Southwest Regional Climate assessment workshop that was held August 1-4, 2011, in Denver, CO with more than 80 participants in a series of scoping presentations and workshops. The workshop began the process leading to a foundational Technical Input Report (TIR) report.17ad4429-1321-4e7c-9cd5-3554eb0c3b38 The TIR consists of nearly 800 pages organized into 20 chapters that were assembled by 122 authors representing a wide range of inputs, including governmental agencies, non-governmental organizations, tribes, and other entities. The report findings were described in a town hall meeting at the American Geophysical Union’s annual fall meeting in 2011, and feedback was collected and incorporated into the draft. The chapter author team engaged in multiple technical discussions through more than 15 biweekly teleconferences that permitted a careful review of the foundational TIR17ad4429-1321-4e7c-9cd5-3554eb0c3b38 and of approximately 125 additional technical inputs provided by the public, as well as the other published literature and professional judgment. The chapter author team then met at the University of Southern California on March 27-28, 2012, for expert deliberation of draft key messages by the authors. Each key message was defended before the entire author team prior to the key message being selected for inclusion. These discussions were supported by targeted consultation with additional experts by the lead author of each message, and they were based on criteria that help define “key vulnerabilities, which include magnitude, timing, persistence and reversibility, likelihood and confidence, potential for adaptation, distribution, and importance of the vulnerable system.”3277e83c-e374-4ed5-b0a2-0adadfaf118d

Description of evidence base: The key message and supporting text summarizes extensive evidence documented in the Technical Input Report.17ad4429-1321-4e7c-9cd5-3554eb0c3b38 Several studies document potential coastal flooding, erosion, and wind-driven wave damages in coastal areas of California due to sea level rise (for example, Bromirski et al. 2012; Heberger et al. 2011, and Revell et al. 20115c646fe6-64d5-459a-8269-c9a994a640a6 fcb5af3b-0831-4b92-83c9-ef197f429982 d37ad258-9d4e-4e80-b99a-4ec70c2bd115). Global sea level has risen, and further rise of 1 to 4 feet is projected by 2100 (Ch. 2: Our Changing Climate, Key Message 10). All of the scientific approaches to detecting sea level rise come to the conclusion that a warming planet will result in higher sea levels. In addition, numerous recent studiesecf211c8-9abc-46ce-bf79-4a12099b02df d8089822-678e-4834-a1ec-0dca1da35314 produce much higher sea level rise projections for the rest of this century as compared to the projections in the most recent report of the Intergovernmental Panel on Climate Change580f7af6-b0eb-4ebb-8da4-ab0a0b8ef68b for the rest of this century.

New information and remaining uncertainties: There is strong recent evidence from satellites such as GRACE0c05253e-78bc-4ca2-80a9-468a42bf0060 5a82ec8d-16e7-4089-b629-ffc99485ce17 5b564190-3aa3-4704-ac92-a1d439727fea 17905d7b-119b-4447-98e2-f5c8b942b69c and from direct observations that glaciers and ice caps worldwide are losing mass relatively rapidly, contributing to the recent increase in the observed rate of sea level rise. Major uncertainties are associated with sea level rise projections, such as the behavior of ice sheets with global warming and the actual level of global warming that the Earth will experience in the future.ecf211c8-9abc-46ce-bf79-4a12099b02df d8089822-678e-4834-a1ec-0dca1da35314 Regional sea level rise projections are even more uncertain than the projections for global averages because local factors such as the steric component (changes in the volume of water with changes in temperature and salinity) of sea level rise at regional levels and the vertical movement of land have large uncertainties.ecf211c8-9abc-46ce-bf79-4a12099b02df However, it is virtually certain that sea levels will go up with a warming planet as demonstrated in the paleoclimatic record, modeling, and from basic physical arguments.

Assessment of confidence based on evidence: Given the evidence, especially since the last IPCC report,580f7af6-b0eb-4ebb-8da4-ab0a0b8ef68b there is very high confidence the sea level will continue to rise and that this will entail major damage to coastal regions in the Southwest. There is also very high confidence that flooding and erosion in coastal areas are already occurring even at existing sea levels and damaging some areas of the California coast during storms and extreme high tides.

References :

• Assessment of Climate Change in the Southwest United States (17ad4429)
• Contribution of Alaskan glaciers to sea-level rise derived from satellite imagery (0c05253e)
• A methodology for predicting future coastal hazards due to sea-level rise on the California Coast (d37ad258)
• Sea-Level Rise for the Coasts of California, Oregon, and Washington: Past, Present, and Future (ecf211c8)
• Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (580f7af6)
• Mapping Greenland's mass loss in space and time (5a82ec8d)
• A Reconciled Estimate of Ice-Sheet Mass Balance (17905d7b)
• Coastal Flooding Potential Projections: 2000–2100. California Energy Commission. CEC-500-2012-011 (5c646fe6)
• Global Sea Level Rise Scenarios for the United States National Climate Assessment. NOAA Tech Memo OAR CPO-1 (d8089822)
• Understanding ice-sheet mass balance: progress in satellite altimetry and gravimetry (5b564190)
• Potential impacts of increased coastal flooding in California due to sea-level rise (fcb5af3b)
• Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (3277e83c)