• Sea ice extent for September 2020 was 3.85 million square km, the second lowest on record (after 2012).
  • The Arctic in 2020 experienced its warmest summer on record. It was also more cyclonic (stormier) than average.
  • There was extreme variation in the rate of ice loss during summer 2020, with two periods of very rapid ice loss separated by a period of very slow ice loss.
  • Predictions of September sea ice extent tended to be on the high side, although some came close to the eventual extent.
  • Antarctic sea ice has likely recorded its seasonal maximum of 18.95 million square km on 27th September, which would represent the 12th highest on record.

September Arctic sea ice extent

Sea ice extent for the month of September 2020 was 3.85 million square km according to the HadISST1.2 dataset (Rayner et al., 2003). This was the second lowest September extent observed in the satellite era (since 1979), after 3.56 million square km in 2012. The 2020 value was 2.54 million square km below the 1981-2010 average, and 0.38 million square km below the long-term linear trend (Figure 1). Extent was exceptionally low in all regions of the Arctic except the Central Arctic and in the Beaufort Sea, where a long ‘arm’ of ice extended along the climatological southern limit of the ice cover (Figure 2). Extent would have been very close to that seen in 2012 (albeit still slightly higher) if this Beaufort Sea ‘arm’ were not present.

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Figure 1. September Arctic sea ice extent during the satellite era, according to HadISST1.2, with linear trend indicated.

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Figure 2. Arctic sea ice extent in September 2020, compared to the record low year of 2012 and the 1981-2010 average, with regions named in the text labelled. Data are from HadISST1.2.

Melt season review

Summer 2020 was exceptionally warm in the Arctic, even more so than in 2019 which was itself record-breaking. As measured by the NCEP reanalysis (Kalnay et al., 1996), the May-August average 925 hPa temperature north of 70°N was the warmest on record (since 1948, Figure 3). Temperatures were warm Arctic-wide, but especially in the Central Arctic and in the Laptev and Kara Seas north of Siberia (Figure 4a). The most notable feature of the summer circulation was a high-pressure ridge over Siberia, most prominent from mid-June to mid-July. As well as circulating very warm air into the Arctic Ocean itself, this caused a notable heatwave in Eastern Siberia, with a provisional new record temperature of 38°C observed in Verkhoyansk. There was also a tendency for the weather to be rather stormy and cyclonic in the central Arctic itself (Figure 4b), particularly early in the season.

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Figure 3. Average May-August temperature anomaly (°C), relative to the 1981-2010 average at 925 hPa over the Arctic Ocean region, for the years 1948-2019. Data are from the NCEP reanalysis.