ETH researchers reveal why Arctic sea ice began to melt in the middle of winter two years ago – and that the increased melting of ice in summer is linked to recurring periods of fair weather.
In the winter of 2015/16, something happened that had never before been seen on this scale: at the end of December, temperatures rose above zero degrees Celsius for several days in parts of the Arctic. Temperatures of up to eight degrees were registered north of Svalbard. Temperatures this high have not been recorded in the winter half of the year since the beginning of systematic measurements at the end of the 1970s. As a result of this unusual warmth, the sea ice began to melt.
“We heard about this from the media,” says Heini Wernli, Professor of Atmospheric Dynamics at ETH Zurich. The news aroused his scientific curiosity, and a team led by his then doctoral student Hanin Binder investigated the issue. In November 2017, they published their analysis of this exceptional event in the journal Geophysical Research Letters.
In it, the researchers show how these unusual temperatures arose: three different air currents met over the North Sea between Scotland and southern Norway, carrying warm air northwards at high speed as though on a “highway”.
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Image via Sandro Bösch, ETH Zurich