finding 11.1 : key-finding-11-1

Annual average near-surface air temperatures across Alaska and the Arctic have increased over the last 50 years at a rate more than twice as fast as the global average temperature. (Very high confidence)

This finding is from chapter 11 of Climate Science Special Report: The Fourth National Climate Assessment: Volume I.

Process for developing key messages: Annual average near-surface air temperatures across Alaska and the Arctic have increased over the last 50 years at a rate more than twice the global average. Observational studies using ground-based observing stations and satellites analyzed by multiple independent groups support this finding. The enhanced sensitivity of the arctic climate system to anthropogenic forcing is also supported by climate modeling evidence, indicating a solid grasp on the underlying physics. These multiple lines of evidence provide very high confidence of enhanced arctic warming with potentially significant impacts on coastal communities and marine ecosystems

Description of evidence base: The Key Finding is supported by observational evidence from ground-based observing stations, satellites, and data-model temperature analyses from multiple sources and independent analysis techniques.e2086a52-de43-4628-97f8-05fb1c8e1e45 e1ea418d-9ff7-4869-a09e-30672e492a64 275c5633-c650-4405-b6c7-3a8151e11b51 47a5196b-4fba-4fdb-8647-8945627725bb e8458879-e69d-4464-a6cb-c1ee60d0cbf1 a9664a29-554f-4680-a6cd-9264b475d17b 241f3efd-0405-4fcf-995c-b6c5058cf5c7 For more than 40 years, climate models have predicted enhanced arctic warming, indicating a solid grasp on the underlying physics and positive feedbacks driving the accelerated arctic warming.3fe708bb-96e6-4612-b91a-4a981974b900 b3bbc7b5-067e-4c23-8d9b-59faee21e58e 74b2ec95-20d0-4af6-8f4c-08f7a0ae8981 Lastly, similar statements have been made in NCA3,dd5b893d-4462-4bb3-9205-67b532919566 IPCC AR5,47a5196b-4fba-4fdb-8647-8945627725bb and in other arctic-specific assessments such as the Arctic Climate Impacts Assessment6116cc9a-1779-4f9c-9b70-ce7bbe540dc3 and Snow, Water, Ice and Permafrost in the Arctic.2ecb64ff-f4e0-4acd-b049-e5d04f44c57a

New information and remaining uncertainties: The lack of high quality and restricted spatial resolution of surface and ground temperature data over many arctic land regions and essentially no measurements over the Central Arctic Ocean hamper the ability to better refine the rate of arctic warming and completely restrict our ability to quantify and detect regional trends, especially over the sea ice. Climate models generally produce an arctic warming between two to three times the global mean warming. A key uncertainty is our quantitative knowledge of the contributions from individual feedback processes in driving the accelerated arctic warming. Reducing this uncertainty will help constrain projections of future arctic warming.

Assessment of confidence based on evidence: Very high confidence that the arctic surface and air temperatures have warmed across Alaska and the Arctic at a much faster rate than the global average is provided by the multiple datasets analyzed by multiple independent groups indicating the same conclusion. Additionally, climate models capture the enhanced warming in the Arctic, indicating a solid understanding of the underlying physical mechanisms.

It is very likely that the accelerated rate of arctic warming will have a significant consequence for the United States due to accelerated land and sea ice melt driving changes in the ocean including sea level rise threatening our coastal communities and freshening of sea water that is influencing marine ecology.

This finding was derived from figure -.2: Confidence / Likelihood

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