The 2021 Arctic Sea Ice Minimum Extent

The results of the ARCUS Sea Ice Prediction Network August call have been released, and here is the outlook for the 2021 minimum 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:

Next here’s JAXA/ViSHOP extent, generally assumed to be a “2 day average”:

Then there’s the EUMETSAT OSI-SAF version:

and finally, for the moment at least, here is the Alfred Wegener Institute / University of Bremen version:

With September 1st only 3 days away all the assorted extent metrics are above the 5 million km2 level. Will one or more of them manage to get below the SIPN predicted 4.39 million km2 monthly average by September 30th? Will the current “tongue of sea ice” in the Kara Sea survive the summer? How about the multi-year ice still surviving in the Beaufort and Chukchi Seas?

[Edit – September 1st]

Here are the end of August numbers for the “high resolution” AMSR2 metrics:

Extent on August 31st is 4.55 million km2. Unlike JAXA’s AMSR2 extent metric, which has been almost flat for the last couple of days, this one has taken a bit of a tumble. Compaction is currently lowest for the date in the AMSR2 record. Unlike extent!

[Edit – September 15th]

A very tentative minimum is now visible on the JAXA/ViSHOP extent graph. Barring any further declines minimum extent for 2021 was 4.61 million km2 on September 12th.

[Edit – September 17th]

In the continuing Google enforced absence of our favourite UH derived metrics I’ve grafted the newly available AWI high resolution AMSR2 area/extent data onto the existing UH numbers. Here is the result:

The join is invisible, and the high resolution AWI AMSR2 minimum Arctic sea ice extent for 2021 currently stands at 4.38 million km2 on September 13th.

Watch this space!

8 thoughts on “The 2021 Arctic Sea Ice Minimum Extent

  1. Hi Jim,
    Interesting times
    Daily high arctic albedo warming potential anomaly a little lower this year. Very surprised and happy to see a new refreeze, even if only temporary.
    14 days of melting left but very low today.

  2. The NSIDC’s 5 day averaged extent has also now broken the 5 million km² barrier:

    4.98 million km² on September 7th to be precise. JAXA extent is now down to 4.75 million km².

    1. And MASIE bounced up to 5.3 today and DMI has been wiggling up around 5.6-5.8 lately. So what is the right number with the right error bars? Or do we just get to pick our favorite that reinforces our hopes (high or low)? Jim, you seem to favor JAXA – is there a good analysis somewhere as to why that’s better/more reliable? I truly want to know. Has someone published a review of all the different approaches to this one metric?

      1. There is no “right number” Taylor, and I don’t particularly favour JAXA. I do however recommend looking at a wide variety of data/metrics. If I have a “favourite” for concentration/extent it’s the University of Hamburg’s high resolution AMSR2 product. Not only because it uses a 3.125 km grid compared to the NSIDC’s 25 km, but also because (when Google allows!) Wipneus publishes a regional area/extent breakdown.

        There’s a wide range of analyses of the pros and cons of assorted sensors and algorithms. Here’s one from 2014:

        Retrieval of Arctic Sea Ice Parameters by Satellite Passive Microwave Sensors: A Comparison of Eleven Sea Ice Concentration Algorithms

        and another preprint that’s only just been published:

        Satellite Passive Microwave Sea-Ice Concentration Data Set Inter-comparison using Landsat data

        1. Useful studies Jim, thanks. I note with interest that NSIDC seems to have bottomed at 4.9, DMI is showing signs of a rebound over the last few days, and MASIE is off its low as well. And it’s that time of year. When do you think you’ll be ready to call the minimum here? Who do you think will have the lowest min, and who the highest? Any prediction on the final spread (date/amount)?

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