<snip>So what I looked at was the Kara and Laptev volume and thickness data as both seas (especially the Laptev) melted out very early in 2020 and freeze commenced very late. And what do we see?
I think Gero's thickness and volume graphs tell an ominous story for the near-future of the Kara Sea ice.
From the sketchy data I have, thickness of ASI does not appear to have much effect on melt rate until it gets below 1.5 meter. But once it gets below 1.0 meter, the melt rate for the same amount of energy input begins to be more than 10% greater than for 2 meter thick ice.
The Kara thickness chart shows the annual max thickness declining from ca. 1.6 meters in 2000s to 1.2 in the 2010s. If that decadal trend continues into the 2020s, the average Kara max thickness would be well below 1.0 and nearing 0.8 meter. Heading into the melt season with ice that is < 0.8-0.9 meter thick is not the same as going in with 1.2 meter thick ice.
This is exacerbated by progressive volume losses. Between the 2000s and 2010s, the Kara went from not melting out entirely to hitting zero volume for about 6 weeks. The average max volume went from ca. 1.25 km3 in the 2000s down to ca. 0.95 km3 in the 2010s. Inevitably, the 2020s average Kara max volume will be even lower. Carrying even less ice into melt season than the amount that already hits zero by mid-August, compounded by having that ice being of a lesser thickness, means that the Kara is on its way out as a major contributor to ASI for much of the year.
The date for the Kara Sea getting down to 0.1 km3 ice shifted from Sept 1. in the 2000s back to mid-July for the 2010s. I suppose the rate of shift will get slower as the date moves into early July and late June and thus closer to the annual max. But it also true that any open water in June at the peak of solar insolation is bad news for albedo and increased ocean warming.
For the refreeze season, the date at which Kara volume heads above 1.0 km3 shifted from Oct. 1 in the 2000s to a month later at Nov. 1 for the 2010s. Given the cumulative effects of continued warming; with lower volume, thickness, and albedo during the melt season; that shift could continue with refreeze not exceeding 0.1 km3 until December 1 for the 2020s. The net result would be a Kara Sea almost devoid of ice for July 1 - Dec. 1, and just starting to recover ice until Jan. 1. If this scenario unfolds, then within the next 5 years, 10 years at most, for 6 months of the year, the Kara Sea will no longer be a significant reservoir of ASI. It was already ice-free for 3 full months in 2020.
Losing the Kara as a defensive perimeter for much of the year allows it to join the Greenland and Barents Seas as melt incursion doorways into the heart of the CAB.
(Ignore the green BOE text on first chart below, the thing to look at is the upward curving blue line showing the effect of diminishing thickness for increasing melt rate.)