The Arctic melting season has begun!
23 June 2020
In the Arctic, the melting season is now well underway. The sea-ice extent is currently below two standard deviations from the long-term average and below the trend in 2019 (Figure 1). From early May to mid-June, the sea-ice concentration shrank by 2.68 million km². Throughout the month of May, it declined by an average of 59,600 km² per day; the monthly mean extent was 11.96 million km² (see Figure 2), making it the third-lowest value for this month since the beginning of satellite observation. Further, the monthly mean extent was 133,7501 km² below the long-term average for 1981 to 2010, but 155,671 km² above the record low in May 2016 (see Figure 3). The sea-ice retreat predominantly took place in the Barents and Kara Seas, and in Denmark Strait (Figure 4). Numerous polynyas formed along the Russian coast, a pattern that has manifested regularly in the past several years, and a somewhat unusually large area of open water formed in the sea ice to the north of Svalbard. In addition, the North Water Polynya, which forms every year in the northern part of Baffin Bay and southern Smith Sound between 76° and 79° North and between 70° and 80° West, appeared.
The linear loss of sea-ice extent, including 2020, is 3.3 % per decade for the month of May in comparison to the long-term average. That equates to an annual loss of ca. 43,900 km² or an area roughly the size of North Rhine-Westphalia. In the 42 years of satellite observation, the Arctic has lost a total of 1.34 million km² of ice in the month of May, based on the difference between the linear trends from 2020 and 1979: an area four times the size of Norway.
The air temperature at 925 hPa was unusually high over nearly all of the Arctic Ocean, with variations of up to 7 °C over the central Arctic Ocean and western Russia (Figure 5). In some parts of Siberia, the temperatures were 10 °C above the long-term average. In contrast, in Canada’s High North, the temperatures were 3 – 5 °C below average. Pressure at sea level was particularly low over Scandinavia and the Central Arctic, while pressure over the Canadian Arctic Archipelago was quite high compared to the long-term average. However, there were no signs of the unusually warm May at the German-French research station AWIPEV on Spitsbergen (Figure 6).
From mid-December to early spring the Arctic Oscillation, a central pattern of atmospheric variability over the Arctic and the North Atlantic, exhibited a prolonged positive (cyclonal) phase. Such an extended period of stability, which continued until early May, is highly unusual and could be connected to an extremely cold stratospheric polar vortex and the largest hole in the ozone of the Arctic stratosphere ever observed. There are certain interdependencies in the atmosphere: events in the stratosphere influence what happens below it (in the troposphere), and vice versa.
Accordingly, the cyclonal (counter-clockwise) circulation at the surface, which was due to the positive AO, was connected to the cyclonal circulation of the cold and intense stratospheric vortex. These extremely stable and cold atmospheric conditions are conducive to the formation of polar stratospheric clouds, which in turn promote ozone loss through chemical processes.
Sea ice in the Antarctic at an average level
In the Antarctic, the trend reversal seen in the past few months continues. After unusually low sea-ice extents in May 2017, 2018 and 2019, this year a more average ice concentration in comparison to the long-term average has established itself (Figure 7). Compared to May 2019, more sea ice can especially be found in the Weddell, Bellingshausen and D’Urville Seas (Figure 8); the extent has only declined in the Amundsen, Ross Meer and Lazarev Seas. This trend continued in the first half of June, with the sea-ice extent mirroring the long-term average (Figure 9).