The Arctic Spring Has Begun
14 April 2021
The seasonal maximum sea-ice extent in the Arctic has come and gone, the sun now rises above the horizon again at the North Pole, and the long Polar Night has come to an end. The mean sea-ice extent for March 2021 in the Arctic was 14.72 million square kilometres (Fig. 1), placing it ca. 504,000 square kilometres above the record low from 2017 and ca. 620,000 square kilometres below the long-term average from 1981 to 2010. In terms of satellite-based observations, which began in 1979, the mean extent is the tenth lowest (Fig. 2). On the Atlantic side, there was less sea ice than the long-term average in the northern Barents Sea and north of Svalbard; on the Pacific side, this was the case in the Chukchi Sea (s. Figure 3). In the Sea of Okhotsk and the eastern Barents Sea, the ice cover was slightly above than the long-term average.
In March, the air temperatures at 925 hPa (ca. 760 metres above sea level) were up to 5 degrees Celsius below average in northern Eurasia, and ranged over Alaska to the east. In contrast, in the Atlantic sector of the Arctic the temperatures were 1 to 3 degrees Celsius above average, with a ‘tongue’ of above-average temperatures extending into the Beaufort Sea (Figure 4, left). The accompanying atmospheric circulation during March was characterised by low pressure over the northern North Atlantic, with the lowest pressure concentrated over the Barents Sea. As a result, colder temperatures from the Arctic were transported to Northern Europe, producing the cold snaps typical for the time of year, especially in the second half of the month. After experiencing a prolonged negative phase for the majority of the winter, the Arctic Oscillation was predominantly positive in March, though there were also significant fluctuations. This is indicative of more westerly winds, which bring warmer Atlantic air to Northern Europe.
Through 2021, the linear rate of decline for the sea-ice extent in March in comparison to the long-term average from 1981 to 2010 is 2.2 percent per decade. The cumulative ice loss in March over the 43-year-long satellite record is 1.39 million square kilometres, an area roughly the size of Peru, based on the difference in the linear trend values in the years 2021 and 1979. The sea-ice concentration is currently at the lower end of two standard deviations from the long-term average (s. Figure 5), which indicates intensifying melting.