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PUBLISHED ONLINE: 26 OCTOBER 2014 | DOI: http://www.nature.com/doifinder/10.1038/ngeo2277
Web End =10.1038/NGEO2277
Masato Mori1*, Masahiro Watanabe1, Hideo Shiogama2, Jun Inoue3 and Masahide Kimoto1
Over the past decade, severe winters occurred frequently in mid-latitude Eurasia1,2, despite increasing global- and annual-mean surface air temperatures3. Observations suggest that these cold Eurasian winters could have been instigated by Arctic sea-ice decline2,4, through excitation of circulation anomalies similar to the Arctic Oscillation5. In climate simulations, however, a robust atmospheric response to sea-ice decline has not been found, perhaps owing to energetic internal uctuations in the atmospheric circulation6. Here we use a 100-member ensemble of simulations with an atmospheric general circulation model driven by observation-based sea-ice concentration anomalies to show that as a result of sea-ice reduction in the BarentsKara Sea, the probability of severe winters has more than doubled in central Eurasia. In our simulations, the atmospheric response to sea-ice decline is approximately independent of the Arctic Oscillation. Both reanalysis data and our simulations suggest that sea-ice decline leads to more frequent Eurasian blocking situations, which in turn favour cold-air advection to Eurasia and hence severe winters. Based on a further analysis of simulations from 22 climate models we conclude that the sea-ice-driven cold winters are unlikely to dominate in a warming future climate, although uncertainty remains, due in part to an insucient ensemble size.
The Siberian High, a continental surface high pressure prevailing the boreal winter Asian monsoon, causes a breakout of cold air to the mid-latitudes, the fluctuation of which greatly aects a significant part of the population of Eurasia. NorthernHemisphere winters (DecemberFebruary; DJF) have frequently seen pronounced warming and cooling in recent years, in theArctic and mid-latitudes, respectively, forming the so-called warmArctic-cold continents pattern7 (Supplementary Fig. 1), signifying the intensification of the Siberian High over the Eurasian continent.The Arctic surface warming has been accompanied by a rapid decline of Arctic sea ice8, which is therefore argued to represent theArctic amplification signature of global warming9,10. However, the
causes of these cold winters observed over mid-latitude Eurasia, apparently counteracting the continuous rise of annual-mean surface air temperature (SAT) over land3, are not well understood.
Observational studies show a statistically significant relationship between cold SAT anomalies over Eurasia and Arctic sea-ice decline2,4,11,12, suggesting that the latter forces the former. However,