Lowest and earliest Arctic sea ice maximum

The northern sea ice has now reached its seasonal maximum extent. This year’s is the lowest and earliest maximum of the satellite era (since 1979). Here’s the US National Snow and Ice Data Center’s sea ice extent chart, with recent years highlighted:

NSIDC northern sea ice extent

There’s been a fair amount of media and general interest in this “yet another dramatic Arctic decline” story.  But most, including many concerned non-specialists, have failed to check the context. Yes, this is another new extreme, but not much of a one. Look at Walsh and Chapman’s 100+ year Arctic sea ice extent compilation (as plotted at Cryosphere Today):

Walsh and Chapman northern sea ice extent compilation

The top trace (blue line) is the estimated northern winter average ice extent. Notice that it shows by far the smallest decline of the four season. The chart is not up to date for 2012-2015, but we can quickly fix that. The NSIDC new record low maximum is 14.5 M.km², but the winter average (they use January-February-March) is of course smaller — a bit under 14 M.km². On the Walsh and Chapman reconstruction that’s clearly a new record low — and a 100+ year one — but it’s hardly unexpected or dramatic.

In fact most of this year’s reduction is not in the Arctic basin at all; it’s in the Sea of Okhotsk north of Japan and the Bearing Sea between Kamchatka and Alaska:

NSIDC sea ice extent

You can see there the quite small differences between the satellite era median (orange line) and 2015.

Look, Arctic sea ice is in very serious overall decline, but this little observation is nothing much. It reflects a very warm north Pacific — definitely a global warming effect, but probably enhanced by the recent flip of the Pacific Decadal Oscillation. If you want to follow the collapse of Arctic sea ice, watch the volume estimates, particularly PIOMAS:

PIOMAS northern sea ice volume

PIOMAS northern sea ice volume

That continues to show a modest recent recovery, but the anomaly trace has also become hugely erratic in recent years, presumably because the system is changing regimes as the ice greatly shrinks and thins. Will the recovery continue, or will the thing soon plummet again? That’s the interesting question; one that may be rather critical for the immediate future of a lot of people, and not just in the Arctic.

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