A view of the Earth from outer space.

One signal of the transition from summer season to fall within the Northern Hemisphere is the annual minimal level in Arctic sea ice extent. Final yr tied 2016 and 2007 for second place behind 2012’s record-low protection. However after one other heat yr on a warming planet, 2020 hit a decrease mark and claimed the No.2 spot free and clear.

Sea ice is floating, frozen seawater, and so its melting doesn’t materially contribute to sea stage rise, not like glacial ice on land. Sea ice protection in each polar areas grows over the winter and shrinks over the summer season. Within the Arctic, losses backside out and provides method to progress in mid-September. Round this time of yr, scientists watch satellite tv for pc information fastidiously, ready for a number of days of stability or slight progress to name the minimal.

That minimal doubtless occurred on September 15, in keeping with the Nationwide Snow and Ice Knowledge Heart. (It’s doable {that a} bizarre flip of climate might trigger the extent to drop once more to a decrease minimal within the subsequent few days, however this most likely wouldn’t change the numbers a lot.) The middle put the minimal extent at 3.74 million sq. kilometers (1.44 million sq. miles).

For comparability, the common summer season minimal between 1981 and 2010 was 6.25 million sq. kilometers. The file low in 2012 was 3.39 million sq. kilometers. In comparison with 2012, 2020 noticed extra sea ice within the Beaufort Sea however much less within the Laptev and East Greenland Seas.

The winter most extent again on March 5 was the eleventh lowest on file and a bit increased than the previous few years. However the soften season began with excessive heat throughout Siberia, and sea ice extent dropped quickly. In July, a brand new summer season file seemed prefer it could possibly be on the best way, however losses slowed in August, and one other run in early September wasn’t fairly sufficient to push previous 2012.

A number of metrics are used for sea ice, with extent representing the realm of steady protection. However thickness and quantity are additionally essential. Sea ice that survives the summer season tends to thicken over the next winter, however a lot much less ice survives a number of years now. Consequently, sea ice thickness has decreased. And that additionally signifies that the thinner ice can soften and disappear extra shortly over the summer season.

Complete sea ice quantity is estimated by the PIOMAS venture. That is solely up to date month-to-month, so September is just not included but, however August quantity was the third lowest on file.

On the different finish of the world, Antarctic sea ice is approaching its winter most, which happens just a few weeks later. Extent there’s wanting like the best since 2014’s satellite-era file and falls above the 1973-2019 common. Antarctic sea ice is significantly extra variable from year-to-year and isn’t experiencing fast decline just like the Arctic. That’s as a result of the Antarctic is experiencing much less warming and since the ocean ice has a frigid continent to develop round.

However for the Arctic, the Nationwide Snow and Ice Knowledge Heart notes, the 14 lowest summer season sea ice extents within the satellite tv for pc period have been… the final 14 years. Floor air temperatures within the Arctic are warming at about three times the global average, resulting in profound local weather, ecosystem, infrastructure, and even geopolitical impacts.

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