Arctic sea-ice extent continues to show significant decline
15 July 2020
At the beginning of summer in the Northern Hemisphere, and with it, of midsummer north of the Arctic Circle, the Arctic sea-ice extent remains quite low. For the majority of June and at the beginning of July, the extent was below the level for the same month in the record-breaking year 2019 (Fig. 1). The monthly mean ice extent was 10.03 million km² – making it, together with 2019, the lowest recorded value since 1979, when continuous satellite observation began (mean value in 2019: 10.03 million km²) (Fig. 2). Particularly in the Russian Arctic, extensive sections of the coastal region were ice-free, especially in the Kara and Laptev Seas (Fig. 3). In late June and early July, a broad coastal polynya formed in the East Siberian Sea, which had never before happened at this time of year (Fig. 4). In contrast, the sea-ice retreat in the Canadian Arctic was less extreme than last year, and was closer to the long-term average. The sea ice decline in the Russian Arctic was due to a pronounced temperature anomaly over the northern Siberian Arctic in June, which climbed to more than six degrees above the long-term average for 1971 – 2000 (Fig. 5). In the Sakha region (East Siberia), temperatures up to 38 °C were reached north of the Arctic Circle; at this time of year, 20 °C is typical. These high temperatures can lead to wildfires and accelerate the thawing of permafrost, with far-reaching consequences for the environment and infrastructure, along with the release of methane, a greenhouse gas 20 times as harmful to the climate as CO2. This prolonged heat island, which formed in May, could be connected to a weakening of the atmospheric jet stream, and to increased meandering in the atmospheric circulation pattern (see also Fig. 5 (right); for more information, click here). In May, there was considerably less snow cover than in the previous year, which led to an increased ice albedo effect and subsequent warming. As a result, the permafrost began thawing, with serious consequences for the infrastructure and interactions between the land surface and atmosphere.
In June, a high-pressure cell formed in the troposphere at 500 hPa (Fig. 5 (centre), transporting warm air into the region. Low precipitation and reduced soil moisture helped to reinforce these high-pressure atmospheric conditions. The entire effect is connected to ‘quasi-resonant amplification of planetary waves’ (QRA), an atmospheric pattern conducive to extreme weather conditions, e.g. the long, hot summer and precipitation extremes in Europe in 2018. For more information, click here. In the early summer of 2020, QRA led to extremely hot conditions in Siberia; in Southwest Europe, it produced heavy rains and flooding in Hungary, Poland, Slovakia and the Czech Republic.