Tuesday, October 4, 2022

Sea Ice Update

It's October again, and that means the time of year when temperatures have changed most dramatically for Alaska's Arctic coast in recent decades.  Here's Rick's comment on Utqiaġvik temperatures from last year:


If we calculate the 50-year linear trend in temperature for each day of the year, and then apply some generous smoothing, we find that warming has actually been most pronounced around November 1.  The 50-year change peaks at about +18°F, or +10°C.  I dare say you won't find a more dramatic example of "Arctic Amplification", i.e. increased warming trends in the Arctic relative to the rest of the globe.

October and November are the key warming months because this is when sea ice coverage has changed the most for the waters near the Arctic coast.  In the absence of ice, open water gives off vast heat fluxes that greatly warm the much colder air above in the early Arctic winter; but when ice closes in, that heat source is considerably reduced.  Consequently, warming trends are most amplified at the time of year when ice extent is most reduced.

Here are the trends in ice concentration since 1979 for September through November, according to NSIDC:

Notice how the zone of critical ice loss is well to the north of Alaska in September.  Even in the early years of the satellite era, ice was not generally widespread along Alaska's north coast in September, although it certainly did happen in some years.  The change has been more pronounced in October for the Beaufort Sea and in November for the Chukchi Sea, leading to peak warming more than a month after the equinox.

While we're on the topic of sea ice, NSIDC provided a written update today, and it's well worth reading:


Minimum Arctic ice extent was on September 18 and was the 10th lowest on record, while the September average ice extent was the 11th lowest on record:


Both the (Russian) Northern Sea Route and the (Canadian) Northwest Passage were open; earlier speculation that the NSR might not open this year was incorrect.

Compared to last year, ice extent started out relatively strong this summer (July into mid-August), but in the end the minimum extent was nearly the same, after rapid losses from mid-August to mid-September.  The most recent year with a significantly higher minimum was 2014.

As for ice volume, the PIOMAS model shows a slight gain over last year, and again 2014 was the most recent year with a significantly higher volume.

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