One sign of the transition from summer to fall in the Northern Hemisphere is the annual minimum point in Arctic sea ice extent. Last year tied 2016 and 2007 for second place behind 2012s record-low coverage. But after another warm year on a warming planet, 2020 hit a lower mark and claimed the No.2 spot free and clear.

Sea ice is floating, frozen seawater, and so its melting does not materially contribute to sea level rise, unlike glacial ice on land. Sea ice coverage in both polar regions grows over the winter and shrinks over the summer. In the Arctic, losses bottom out and give way to growth in mid-September. Around this time of year, scientists watch satellite data carefully, waiting for several days of stability or slight growth to call the minimum.

That minimum likely occurred on September 15, according to the National Snow and Ice Data Center. (Its possible that a weird turn of weather could cause the extent to drop again to a lower minimum in the next few days, but this probably wouldnt change the numbers much.) The center put the minimum extent at 3.74 million square kilometers (1.44 million square miles).

It's official. 2020's #Arctic sea ice minimum was the 2nd lowest ever observed. The long-term trend is clear ?

+ Press release (@NSIDC): https://t.co/fBUTSWE0OD
+ Extremes from this summer ? https://t.co/7p5Y7YZp03 pic.twitter.com/po1M2DSIJa

— Zack Labe (@ZLabe) September 21, 2020

For comparison, the average summer minimum between 1981 and 2010 was 6.25 million square kilometers. The record low in 2012 was 3.39 million square kilometers. Compared to 2012, 2020 saw more sea ice in the Beaufort Sea but less in the Laptev and East Greenland Seas.

The winter maximum extent back on March 5 was the 11th lowest on record and a bit higher than the last few years. But the melt season started with extreme warmth across Siberia, and sea ice extent dropped rapidly. In July, a new summer record looked like it could be on the way, but losses slowed in August, and another run in early September wasnt quite enough to push past 2012.

  • Average summer minimum extent for 1981-2010 is shown with the yellow line. NSIDC
  • Here's how 2020's minimum compares to 2012. NSIDC
  • Here's how extent has played out over 2020 (blue) compared to the record low (red) and the 1981-2010 average (gray). NSIDC
  • This estimate of Arctic sea ice volume hasn't yet been updated for September, but August was 3rd lowest. PIOMAS

Several metrics are used for sea ice, with extent representing the area of continuous coverage. But thickness and volume are also important. Sea ice that survives the summer tends to thicken over the following winter, but much less ice survives multiple years now. As a result, sea ice thickness has decreased. And that also means that the thinner ice can melt and disappear more quickly over the summer.

Total sea ice volume is estimated by the Read More – Source

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