finding 22.2 : glacier-shrinkage-implications

Most glaciers in Alaska and British Columbia are shrinking substantially. This trend is expected to continue and has implications for hydropower production, ocean circulation patterns, fisheries, and global sea level rise.

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 Technical Input Report.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. Evidence that glaciers in Alaska and British Columbia are shrinking is strong and is based on field studies,2c0068c4-bde0-4d10-8d9b-9135868ec825 16e8187e-a734-4d60-ae4c-95021657d756 energy balance models,c426adb7-b055-4726-80f1-82d7846f46c0 LIDAR remote sensing,b6bd09ac-2fd9-4720-b8a3-089a37a42e95 0a0ac996-a92d-4584-9d24-f94dd27844c6 and satellite data, especially new lines of evidence from the Gravity Recovery and Climate Experiment (GRACE) satellite.0c05253e-78bc-4ca2-80a9-468a42bf0060 0a0ac996-a92d-4584-9d24-f94dd27844c6 f755e69d-3511-4ec0-baab-4c1d0663888e 5b564190-3aa3-4704-ac92-a1d439727fea Evidence is also strong that Alaska ice mass loss contributes to global sea level rise,6e84ea40-9754-4273-9281-f8d6fc563917 with latest results permitting quantitative evaluation of losses globally.7578c40e-dfbf-435c-bb83-36eada4f0095 Numerous peer-reviewed publications describe implications of recent increases, but likely longer-term declines, in water input from glacial rivers to reservoirs and therefore hydropower resources.09961450-e217-4cf4-b11f-fab19c8ea9ed 6e174e7d-28f7-4ce4-9141-c378d82b4f53 3132328b-bb58-47c8-a3b2-53054951f331 Glacial rivers account for 47% of the freshwater input to the Gulf of Alaska3132328b-bb58-47c8-a3b2-53054951f331 and are an important source of organic carbon,dbc23531-4169-4dad-bfbd-fac80c5f40bb cc023336-fbff-49f7-a87f-d5353f24c903 phosphorus,a955e6c1-f593-435f-aea3-61fc83bfd7b8 and irone27d4082-48ed-4f8b-a477-dfabe8e4b40e that contribute to the high productivity of near-shore fisheries.cc023336-fbff-49f7-a87f-d5353f24c903 7312e00b-5455-4a22-9ad9-dd805a462473 27f2a255-5137-466d-a34d-6899eb4132fa 93088c9e-c280-4065-88cf-934e8de6697f Therefore, it is projected that the changes in discharge of glacial rivers will affect ocean circulation patterns and major U.S. and locally significant fisheries.

New information and remaining uncertainties: Important new evidence confirmed many of the findings from a prior Alaska assessment (, which informed the 2009 NCA.e251f590-177e-4ba6-8ed1-6f68b5e54c8a As noted above, major advances from GRACE and other datasets now permit analyses of glacier mass loss that were not possible previously. Key uncertainties remain related to large year-to-year variation, the spatial distribution of snow accumulation and melt, and the quantification of glacier calving into the ocean and lakes. Although most large glaciated areas of the state are regularly measured observationally, extrapolation to unmeasured areas carries uncertainties due to large spatial variability. Although there is broad agreement that near-shore circulation in the Gulf of Alaska is influenced by the magnitude of freshwater inputs, little is known about the mechanisms by which near-term increases and subsequent longer-term decreases in glacier runoff (as the glaciers disappear) will affect the structure of the Alaska Coastal Current and smaller-scale ocean circulation, both of which have feedback on fisheries. The magnitude and timing of effects on hydropower production depend on changes in glacial mass, as described above.

Assessment of confidence based on evidence: High confidence that glacier mass loss in Alaska and British Columbia is high, contributing 20% to 30% as much to sea level rise as does shrinkage of the Greenland Ice Sheet. High confidence that due to glacier mass loss there will be related impacts on hydropower production, ocean circulation, fisheries, and global sea level rise.

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