Sea ice has emerged as the canary in the coal mine of climate change. Its summer extent in the Arctic has decreased by about 50% over the past decade, and the Arctic Ocean has undergone a regime shift from a cover of thick multiyear ice to a largely seasonal and much thinner ice cover. The recent loss is unprecedented in the periods of satellite and historical records of sea ice, and it also appears to be unique in paleo reconstructions spanning more than a thousand years. A “perfect storm” of warmer atmospheric and oceanic forcing, together with a boost from natural variability of wind forcing in some years, drove the change. However, the reduction of ice coverage is not apparent in some sub-Arctic regions during the winter, nor has it occurred in the Antarctic region.

Signals of a response to the loss of sea ice are emerging in the ocean and the atmosphere. Ocean heat storage during the ice-free season not only contributes to a later freeze-up than in the past, but it also reduces the thickness to which first-year ice can grow. The vulnerability of this thinner ice to rapid spring melt is a manifestation of the ice-albedo-temperature feedback that has long been postulated as a contributor to polar amplification of climate change. More notably for middle latitudes, the loss of sea ice appears to be triggering a reduction of the large-scale westerlies that characterize atmospheric circulation in middle and subpolar latitudes. This response is consistent with increased persistence of departures from normal temperature, precipitation, and extreme weather during autumn and winter in heavily populated areas of the Northern Hemisphere.

Walsh, J.E. 2013. Melting ice: What is happening to Arctic sea ice, and what does it mean for us? Oceanography 26(2):171–181, https://doi.org/10.5670/oceanog.2013.19.

Alexeev, V.A.,V.V. Ivanov, R. Kwok, and L.H. Smedsrud. 2013. North Atlantic warming and declining volume of arctic sea ice. The Cryosphere Discussions 7:245–265, https://doi.org/10.5194/tcd-7-245-2013.

AMAP (Arctic Monitoring and Assessment Programme). 2011. Snow, Water, Ice and Permafrost in the Arctic-SWIPA. Arctic Monitoring and Assessment Programme, Oslo, Norway, 668 pp.

Beszczynska-Möller, A., R.A. Woodgate, C. Lee, H. Melling, and M. Karcher. 2011. A synthesis of exchanges through the main oceanic gateways to the Arctic Ocean. Oceanography 24(3):82–99, https://doi.org/10.5670/oceanog.2011.59.

Cohen, J.L., J.C. Furtado, M.A. Barlow, V.A. Alexeev, and J.C. Cherry. 2012. Arctic warming, increasing snow cover and widespread wintertime boreal cooling. Environmental Research Letters 7, 014007, https://doi.org/10.1088/1748-9326/7/1/014007.

Francis, J.A., and S.J. Vavrus. 2012. Evidence linking Arctic amplification to extreme weather in mid-latitudes. Geophysical Research Letters 39, L06801, https://doi.org/10.1029/2012GL051000.

Grebmeier, J.M., J.E. Overland, S.E. Moore, E.V. Farley, E.C. Carmack, L.W. Cooper, K.E. Frey, J.H. Helle, F.A. McLaughlin, and S.L. McNutt. 2006. A major ecosystem shift observed in the northern Bering Sea. Science 311:1,461–1,464, https://doi.org/10.1126/science.1121365.

Honda, M., J. Inoue, and S. Yamane. 2009. Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters. Geophysical Research Letters 36, L08707, https://doi.org/10.1029/2008GL037079.
(IPCCP) Intergovernmental Panel on Climate Change. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 996 pp.

Kaufman, D.S., D.P. Schneider, N.P. McKay, C.M. Ammann, R.S. Bradley, K.R. Briffa, G.H. Miller, B.L. Otto-Bliesner, J.T. Overpeck, B.M. Vinther, and Arctic Lakes 2K Project Members. 2009. Recent warming reverses long-term Arctic cooling. Science 325:1,236, https://doi.org/10.1126/science.1173983.

Kay, J.E., M.M. Holland, and A. Jahn. 2011. Inter-annual to multi-decadal Arctic sea ice extent trends in a warming world. Geophysical Research Letters 38, L15708, https://doi.org/10.1029/2011GL048008.

Kinnard, C., C.M. Zdanowicz, D.A. Fisher, E. Isaksson, A. de Vernal, and L.G. Thompson. 2011. Reconstructed changes in Arctic sea ice over the past 1,450 years. Nature 479:509–512, https://doi.org/10.1038/nature10581.

Liu, J., J.A. Curry, H. Wang, M. Song, and R.M. Horton. 2012. Impact of declining Arctic sea ice on winter snowfall. Proceedings of the National Academy of Sciences of the United States of America, https://doi.org/10.1073/pnas.1114910109.

Overland, J.E., and M. Wang. 2010. Large-scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice. Tellus 62A:1–9, https://doi.org/10.1111/j.1600-0870.2009.00421.x.

Perovich, D., W. Meier, M. Tschudi, S. Gerland, and J. Richter-Menge. 2013. Sea ice. Arctic Report Card: Update for 2012. Available online at http://www.arctic.noaa.gov/reportcard/sea_ice.html (accessed May 2, 2013).

Perovich, D., and J. Richter-Menge. 2009. Loss of sea ice in the Arctic. Annual Review of Marine Science 1:417–441, https://doi.org/10.1146/annurev.marine.010908.163805.

Polyakov, I.V., V.A. Alexeev, U.S. Bhatt, E.I. Polyakova, and X. Zhang. 2010. North Atlantic warming: Patterns of long-term trends and multidecadal variability. Climate Dynamics 34:439–457, https://doi.org/10.1007/s00382-008-0522-3.

Screen, J.A., and I. Simmonds. 2013. Exploring links between Arctic amplification and mid-latitude weather. Geophysical Research Letters 40:959–964, https://doi.org/10.1002/grl.50174.

Serreze, M.C., A.P. Barrett, and J.C. Stroeve. 2012. Recent changes in tropospheric water vapor over the Arctic as assessed from radiosondes and atmospheric reanalyses. Journal of Geophysical Research 117, D10104, https://doi.org/10.1029/2011JD017421.

Serreze, M.C., A.P. Barrett, J.C. Stroeve, D.N. Kindig, and M.M. Holland. 2009. The emergence of surface-based Arctic amplification. The Cryosphere 3:11–19, https://doi.org/10.5194/tc-3-11-2009.

Serreze, M.C., and J.A. Francis. 2006. The Arctic amplification debate. Climate Dynamics 76:241–264, https://doi.org/10.1007/s10584-005-9017-y.

Shakhova, N., I. Semiletov, A. Salyuk, V. Yusupov, D. Kosmach and O. Gustafsson. 2010. Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic shelf. Science 327:1,246–1,250, https://doi.org/10.1126/science.1182221.

Shimada, K., T. Kamoshida, M. Itoh, S. Nishino, E. Carmack, F. McLaughlin, S. Zimmerman, and A. Proshutinsky. 2006. Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean. Geophysical Research Letters 33, L08605, https://doi.org/10.1029/2005GL025624.

Stroeve, J.C., M.C. Serreze, M.M. Holland, J.E. Kay, J. Maslanik, and A.P. Barrett. 2011. The Arctic’s rapidly shrinking sea ice cover: A research synthesis. Climatic Change 110:1,005–1,027, https://doi.org/10.1007/s10584-011-0101-1.

Stroeve, J.C., V.M. Kattsov, A.P. Barrett, M.C. Serreze, A. Pavlova, M.M. Holland, and W.N. Meier. 2012. Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations. Geophysical Research Letters 39, L16502, https://doi.org/10.1029/2012GL052676.

Thompson, D.W.J., and J.M. Wallace. 1998. The Arctic oscillation signature in the wintertime geopotential height and temperature fields. Geophysical Research Letters 25 (9):1,297–1,300, https://doi.org/10.1029/98GL00950.

Zhang, J., Y.H. Spitz, M. Steele, C. Ashjian, R. Campbell, L. Berline, and P. Matrai. 2010. Modeling the impact of declining sea ice on the arctic marine planktonic ecosystem. Journal of Geophysical Research 115, C10015, https://doi.org/10.1029/2009JC005387.

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