Data | Arctic sea ice extent in October 2020 was the lowest on record for any October

The Arctic Ocean did not see its typical rate of refreezing in 2020

December 24, 2020 10:50 pm | Updated 10:50 pm IST

Arctic summer sea ice levels have declined by more than 10% each decade since the late 1970s and mountain glaciers have shed roughly 250 billion tonnes of ice annually over the last century.

Arctic summer sea ice levels have declined by more than 10% each decade since the late 1970s and mountain glaciers have shed roughly 250 billion tonnes of ice annually over the last century.

In 2020, the extent of the Arctic sea ice was at its second lowest in history. More worrying was the fact that after reaching the minimum extent on September 15, the ice grew back at a slower pace than usual due to the Arctic region’s unusually warm October. Due to the slow refreeze after mid-September, the Arctic sea ice extent in October was the lowest on record for any October.

Slow refreeze

From mid-March to mid-Sept., the ice in the Arctic region melts. It refreezes from mid-Sept. to mid-March. The graph shows this process by depicting the average sea ice extent — defined as the area in which the ice concentration is at least 15 % — in the Arctic. In 2020 (the red line) , the Arctic ice cap shrank to 3.74 million sq km, making it the second-lowest minimum on record after 2012 (the black line).

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Unlike in 2012, the Arctic Ocean did not see its typical rate of refreezing in 2020. So, the ice extent in October 2020 was lowest for any October.

Also read: Data | Sea ice extent in Arctic lowest in July since 1979; in Antarctic, it surpassed average level in Sept.

On thin ice

The map shows the average sea ice extent for Oct. 2020 (white), measuring 5.28 million sq km against the 1981-2010 October average (yellow line). The Oct. 2020 extent was 3.07 million sq km lower than the average.

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Why quick melt and slow refreeze?

Variations in water temperatures and weather can affect the Arctic sea ice. Starting in May, warm air over Siberia led to rapid melting of ice in the East Siberian and Laptev seas. With large expanses of dark, ice-free water, the ocean was exposed to more heat than usual in the summer, which led to more melting. Until that heat escaped into the atmosphere, sea ice could not regrow, thus delaying the Arctic Ocean’s refreeze. The bar graph shows that unusually warm air persisted into October 2020.

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