Briefing on Arctic sea ice - September 2020
Alex West and Ed Blockley
Arctic sea ice minimum
Arctic sea ice reached a minimum extent of 3.74 million square km on the 15th September 2020, according to data from the National Snow and Ice Data Center (Figure 1). This is the 2nd lowest minimum sea ice extent in the satellite era (since 1979), the lowest having been recorded in 2012 at 3.39 million square km. The 2020 minimum sea ice extent is 2.49 million square km below the 1981-2010 average, and 0.38 million square km below the long-term linear trend (Figure 2).
Figure 1. Daily Arctic sea ice extent for 2020, compared with recent years, and the 1981-2010 average with +/- 1 and 2 standard deviation intervals indicated by the shaded areas. Data are from the National Snow and Ice Data Center (NSIDC)
Figure 2. Arctic sea ice minima from 1979 to 2020 according to the NSIDC Sea Ice Index. The minimum sea ice extent is taken to be the lowest 5-day average.
The extremely low minimum extent follows a summer of very strong variation in sea ice melt rate, with two periods of exceptionally fast ice melting (from late June to mid-July and from mid-August to early September) alternating with a period of very slow ice melt from late July to early August.
Regional conditions
Extent at minimum was exceptionally low in almost all regions of the Arctic, except for in the eastern and southern Beaufort Sea where an ‘arm’ of ice extended away from the main pack along the climatological southern boundary of the ice (Figure 3). This pattern of ice melt reflects a dominant circulation pattern prominent during late June and much of July, associated with a notable Siberian heatwave documented here). During this period, warm air from Siberia was circulated over most of the Arctic, but not the Beaufort Sea, which remained colder than average.
Figure 3. Minimum sea ice extent (15th September 2020), with 1981-2010 average extent for this date indicated in orange. Underlying map and data courtesy of NSIDC