September has arrived and it’s time to start speculating about when and at what level this summer’s minimum Arctic sea ice extent will occur. Here’s a helpful summary of previous years’ JAXA AMSR2/AMSR-E extent minima courtesy of Zack Labe:
Here too is JAXA’s current graph of extent, including a selection of previous years:
JAXA extent on August 31st was 4.96 million km2, marginally below last year’s value of 4.99 million km2 on the same date.
Here’s the latest graph of Arctic sea ice extent from JAXA/ViSHOP, which looks a bit unusual to say the least:
It certainly caught my eye! Could that sudden peak on February 23rd be the maximum extent for the year? To be frank it looks more like an artifact in the underlying gridded AMSR2 concentration data, but it’s not wholly beyond the bounds of possibility. The Pacific side of the Arctic is anomalously warm at the moment:
The results of the ARCUS Sea Ice Prediction Network August call have been released, and here is the outlook for the 2021 minimum September mean Arctic sea ice extent:
The median prediction for the mean sea ice extent during the month of September 2021 is 4.39 million km2. According to ARCUS:
As of 22 August 2021, the Arctic sea-ice extent was 5.58 (compared with 25 August 2020 value of 4.43) million square kilometers. Arctic sea-ice extent in 2021 remains well below the climatological median and has closely followed the 2012 values for much of the summer but has diverged to higher sea-ice extent starting in early August. The forecasts continue to support September 2021 mean sea-ice extent being well above the September 2020 value. July sea-ice retreat has been greatest in the Eurasian seas, particularly in the East Siberian Sea, making the 2021 ice edge well north of the long-term median edge in Eurasia. Sea ice retreated since the end of July along the northern coast of Alaska, although the ice edge is near its climatological position, which makes the Beaufort and Chukchi sea ice extent the largest at this time of year since 2006. A tongue of sea ice that has been present all summer continues to extend close to land in the Kara Sea, making the northeast passage likely to remain blocked for the first time in several years. Half the models which provide spatial data to the SIO predict that the tongue is likely to survive.
Now let’s take a look at a range of assorted extent measurements. Here’s the NSIDC’s 5 day average extent:
Here’s the latest graph of Arctic sea ice extent from JAXA/ViSHOP, with 2021 and 2015 highlighted:
Extent fell by over 100,000 square kilometres between February 16th and 17th! Can that steep fall continue, as it did for one more day in 2015?
Here too is Zack Labe’s 2021 overview of JAXA maximum extent over the previous couple of decades:
2015’s maximum was very early, on February 15th. Hence the current extremely tentative 2021 maximum is already both higher and later than that. The decadal average extent graphs show the date of the maximum getting later and later, and the 2010’s peaks in the middle of March.
It therefore seems likely that there is more freezing still to come this year. However lets take a look at the high resolution AMSR2 sea ice area graph for the Sea Of Okhotsk:
The recent fall in Arctic wide extent has evidently been driven by the recent rapid decline in this peripheral sea, where SMOS reveals more thin ice ripe for further melting:
In conclusion, the high res AMSR2 extent metric shows the tentative 2021 peak below that of 2015!
March 2019 has arrived, which in recent years has proved to be by far the likeliest month to contain the maximum extent of Arctic sea ice for the year. To begin with, here’s our favourite high resolution extent graph calculated by “Wipneus” from University of Hamburg/JAXA AMSR2 data:
September is upon us once again, the month in which the assorted Arctic sea ice area and extent metrics (almost) always reach their respective annual minima. Now we are free to start speculating about what the assorted minima will be, and on what date.
According to the latest edition of the National Snow and Ice Data Center’s “Arctic Sea Ice News”
On March 17, 2018, Arctic sea ice likely reached its maximum extent for the year, at 14.48 million square kilometers (5.59 million square miles), the second lowest in the 39-year satellite record, falling just behind 2017. This year’s maximum extent is 1.16 million square kilometers (448,000 square miles) below the 1981 to 2010 average maximum of 15.64 million square kilometers (6.04 million square miles).
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