An Observational Estimate of the Direct Atmospheric Response to the Arctic Sea Ice Loss

The direct response of the cold season atmospheric circulation to the Arctic sea ice loss is estimated from observed sea ice concentration (SIC) and an atmospheric reanalysis by assuming that the response to the long-term sea ice loss is the same as that to interannual pan-Arctic SIC fluctuations with identical spatial patterns, as given by lag multiple regressions. No significant large-scale field significant response is detected in October, November, or April, and the negative stratospheric and upper tropospheric Arctic Oscillation-like signal that lags the interannual panArctic SIC fluctuations in November is attributed to concomitant Siberian snow cover and tropical Pacific SST fluctuations. However, a robust tropospheric negative NAO-like signal in January, February and, less significantly, March is attributed to the SIC fluctuations, leading to a decrease of blocking activity in the eastern subtropical North Atlantic and an increase in northern Europe. No evidence is found of a pan-Arctic SIC influence on the Warm Arctic Cold Eurasia pattern. Extrapolating these results suggests that, in the absence of other forcings, the direct impact of the SIC loss between 1979 and 2016 would have induced a 2 to 3 °C/decade winter warming in northeastern North America and a Z500 increase of 40 to 60m/decade over Greenland, at least if linearity and perpetual winter conditions could be assumed.