Arctic summer sea ice is receding faster than previously projected and is expected to virtually disappear before mid-century. This is altering marine ecosystems and leading to greater ship access, offshore development opportunity, and increased community vulnerability to coastal erosion.

This finding is from chapter 22 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 Alaska Regional Climate assessment workshop that was held September 12-15, 2012, in Anchorage with approximately 20 attendees; it began the process leading to a foundational Technical Input Report (TIR).6e174e7d-28f7-4ce4-9141-c378d82b4f53 The report consists of 148 pages of text, 45 figures, 8 tables, and 27 pages of references. Public and private citizens or institutions were consulted and engaged in its preparation and expert review by the various agencies and non-governmental organizations (NGOs) represented by the 11-member TIR writing team. The key findings of the report were presented at the Alaska Forum on the Environment and in a regularly scheduled, monthly webinar by the Alaska Center for Climate Assessment and Policy, with feedback then incorporated into the report. The chapter author team engaged in multiple technical discussions via regular teleconferences. These included careful expert review of the foundational TIR6e174e7d-28f7-4ce4-9141-c378d82b4f53 and of approximately 85 additional technical inputs provided by the public, as well as the other published literature and professional judgment. These discussions were followed by expert deliberation of draft key messages by the writing team in a face-to-face meeting before each key message was selected for inclusion in the Report. 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” (Ch. 26: Decision Support).

Description of evidence base: The key message and supporting chapter text summarize extensive evidence documented in the Alaska TIR.6e174e7d-28f7-4ce4-9141-c378d82b4f53 Technical input reports (85) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. Although various models differ in the projected rate of sea ice loss, more recent CMIP5 models6e730a84-66a2-4e74-96cb-c9e6824cf185 that most accurately reconstruct historical sea ice loss project that late-summer sea ice will virtually disappear by the 2030s, leaving only remnant sea ice. Evidence is strong about the impacts of sea ice loss.6e174e7d-28f7-4ce4-9141-c378d82b4f53 Because the sea ice cover plays such a strong role in human activities and Arctic ecosystems, loss of the ice cover is nearly certain to have substantial impacts.9d6e6cea-7b84-4ab3-8b27-b245b3800e4d

New information and remaining uncertainties: Important new evidence confirmed many of the findings from a prior Alaska assessment (http://nca2009.globalchange.gov/alaska), which informed the 2009 NCA.e251f590-177e-4ba6-8ed1-6f68b5e54c8a Evidence from improved models (for example,6e730a84-66a2-4e74-96cb-c9e6824cf185) and updated observational data from satellite, especially new results, clearly show rapid decline in not only extent but also mass and thickness of multi-year ice,f1a5ebbc-6aba-405c-861f-62d88bae060e information that was not available in prior assessments. Nearly all studies to date published in the peer-reviewed literature agree that summer Arctic sea ice extent is rapidly declining and that, if heat-trapping gas concentrations continue to rise, an essentially ice-free summer Arctic ocean will be realized before mid-century. However, there remains uncertainty in the rate of sea ice loss, with the models that most accurately project historical sea ice trends currently suggesting nearly ice-free conditions sometime between 2021 and 2043 (median 2035).6e730a84-66a2-4e74-96cb-c9e6824cf185 Uncertainty across all models stems from a combination of large differences in projections among different climate models, natural climate variability, and uncertainty about future rates of fossil fuel emissions. Ecosystems: There is substantial new information that ocean acidification, rising ocean temperatures, declining sea ice, and other environmental changes are affecting the location and abundance of marine fish, including those that are commercially important, those used as food by other species, and those used for subsistence.34d601bb-7781-4785-bde8-3b10be88994c b33c6aba-d652-4f20-9809-e0948a06bcfd 7ab1d9e1-75a1-48c5-8d85-02258496f919 d8db2d8d-d1d1-4d24-b662-67b26b8ac92b 215b842d-1f34-40c2-8e0e-04965ad303d6 8d612e8b-b96e-48db-a8b4-17bcc3550f7d However, the relative importance of these potential causes of change is highly uncertain. Regarding offshore oil and gas development, a key uncertainty is the price of fossil fuels. Viable avenues to improving the information base are determining the primary causes of variation among different climate models and determining which climate models exhibit the best ability to reproduce the observed rate of sea ice loss. Coastal erosion: There is new information that lack of sea ice causes storms to produce larger waves and more coastal erosion.6e174e7d-28f7-4ce4-9141-c378d82b4f53 An additional contributing factor is that coastal bluffs that were “cemented” by permafrost are beginning to thaw in response to warmer air and ocean waters, and are therefore more vulnerable to erosion.1fb3ac6c-0180-4195-ae1d-5d28ef1ade64 Standard defensive adaptation strategies to protect coastal communities from erosion such as use of rock walls, sandbags, and riprap have been largely unsuccessful.550d81ed-d1b4-4b46-bf5e-ea47ab3e5dea There remains considerable uncertainty, however, about the spatial patterns of future coastal erosion.

Assessment of confidence based on evidence: Given the evidence base and remaining uncertainties: Very high confidence for summer sea ice decline. High confidence for summer sea ice disappearing by mid-century. Very high confidence for altered marine ecosystems, greater ship access, and increased vulnerability of communities to coastal erosion. High confidence regarding offshore development opportunity.

References :

• The Future of Arctic Sea Ice (9d6e6cea)
• Sea ice loss enhances wave action at the Arctic coast (1fb3ac6c)
• Gasping Fish and Panting Squids: Oxygen, Temperature and the Growth of Water-Breathing Animals (d8db2d8d)
• Anticipating ocean acidification’s economic consequences for commercial fisheries (b33c6aba)
• Climate change impacts on the biophysics and economics of world fisheries (8d612e8b)
• Shellfish Aquaculture and the Environment (34d601bb)
• The United States National Climate Assessment— Alaska Technical Regional Report (6e174e7d)
• Climate Change Affects Marine Fishes Through the Oxygen Limitation of Thermal Tolerance (215b842d)
• webpage Adaptation Advisory Group of the Governor’s Sub-Cabinet on Climate Change (550d81ed)
• Global Climate Change Impacts in the United States (e251f590)
• The Arctic’s rapidly shrinking sea ice cover: a research synthesis (f1a5ebbc)
• Ocean Acidification: The Other CO2 Problem (7ab1d9e1)
• A sea ice free summer Arctic within 30 years: An update from CMIP5 models (6e730a84)