Since the beginning of September, Arctic sea ice extent has undergone a sharp decline, reaching its seasonal minimum on 15 September at just 3.74 million square kilometres. Since 1979, the year in which the first satellite monitoring began, this is only the second time it has fallen below 4 million square kilometres. This is what emerges from the preliminary measurements of the US National Snow & Ice Data Center, which will publish its comprehensive analysis of the Arctic summer at the beginning of October.

National Snow and Ice Data Center @NSIDC

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We have called this year's likely #Arctic sea ice minimum extent at 3.74 M sq km (1.44 M sq mi) on September 15. This year's minimum extent is ranked 2nd lowest in the satellite record. Learn more: bit.ly/3mFmx4O. #CUBoulder @CIRES_News @NASA_Earth @NASA_Ice

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The steep decline observed between 31 August and 5 September was driven above all by warm air coming from Siberia, where the summer of 2020 was marked by record heat. From now on, the sea ice is expected to begin expanding again, as temperatures and daylight hours will decrease with the onset of autumn. However, researchers warn that other atmospheric phenomena — such as a shift in wind patterns, for example — cannot be ruled out as potential drivers of a new seasonal minimum in the coming days.

Sea ice: all negative records date back to the last 14 years

On only one previous occasion had satellites recorded a lower extent: on 17 September 2012, when it reached a minimum of 3.39 million square kilometres. Looking at long-term trends, it becomes clear that these figures are no coincidence. Satellite measurements can in fact be divided into three distinct periods of 14 years each. All three show a constant reduction in sea ice area, at an average rate of 6.4 per cent per decade between 1979 and 1992, rising to 13.3 per cent between 1993 and 2006, before returning to 4 per cent between 2007 and 2020. The National Snow & Ice Data Center highlights that all the lowest values have been recorded in the last 14 years.

In the Arctic, global warming is moving faster

Average temperatures in the Arctic are rising at a much faster rate than those in the rest of the world. One of the local mechanisms contributing to this phenomenon, known as polar amplification, is precisely the melting of ice- or snow-covered surfaces. These are white and have a high capacity to reflect solar rays. As they disappear, they leave exposed vast areas of darker open water, which conversely absorb those rays, store heat, and contribute to rising temperatures.