The atmospheric response to three decades of observed Arctic sea ice loss
James A. Screen* and Ian Simmonds (School of Earth Sciences, University of Melbourne, Melbourne, Victoria, Australia) and
Clara Deser and Robert Tomas
(Climate and Global Dynamics, National Center for Atmospheric Research, Boulder, CO, U.S.A.)Abstract
Arctic sea ice is declining at an increasing rate with potentially important repercussions. In order to understand better the atmospheric changes that may have occurred in response to Arctic sea ice loss, we present results from atmospheric general circulation model (AGCM) experiments in which the only time-varying forcings prescribed were observed variations in Arctic sea ice and accompanying changes in Arctic sea surface temperatures from 1979 to 2009. We utilize two independent AGCMs in order to assess the robustness of the response across different models. The results suggest that the atmospheric impacts of Arctic sea ice loss have been manifest most strongly within the maritime and coastal Arctic, and in the lower-most atmosphere. Sea ice loss has driven increased energy transfer from the ocean to the atmosphere, enhanced warming and moistening of the lower troposphere, has decreased the strength of the surface inversion, and increased lower-tropospheric thickness; all these changes are most pronounced in autumn and early winter (September-December). The early winter (November-December) atmospheric circulation response resembles the negative phase of the North Atlantic Oscillation (NAO); however, the NAO-type response is quite weak and is often masked by intrinsic (unforced) atmospheric variability. We also find some evidence of a late winter (March-April) polar stratospheric cooling response to sea ice loss, which may have important implications for polar stratospheric ozone concentrations. The attribution and quantification of other aspects of the possible atmospheric response are hindered by model sensitivities and large intrinsic variability. The potential remote responses to Arctic sea ice change are currently hard to confirm and remain uncertain.
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