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Regular visitors to Cryosphere Today will have noticed that the headline graph of sea ice area covering the whole Arctic has developed a funny little squiggle at the end, and the sea ice loss appears to have come to an abrupt stop, at least for the time being. So what is going on?
If you look at the various regional graphs, something emerges. Almost every area has flatlined at or near zero. It’s hard to reduce ice in areas where there is next to none. The Arctic Basin has increased its sea ice cover. two possible explanations: as it’s the first area where refreezing begins, and surface temperatures are at their lowest, it is possible that some consolidation of the ice pack has occurred, and there are fewer pools or polynyas in this area at the moment. The whole of the Arctic ice also drifts around a bit. With so much open water this year, it is likely that the currents have pushed what little ice was outside the area into the Basin. Indeed, if you then check out the Kara and Laptev seas, you’ll see that the ice area here has continued to decline; some from drift, and some from melt, perhaps.
Two other areas where there have been changes recently are the Canadian Archipelago/Beaufort Sea and the Greenland Sea. The first of these suggest that the ice melt is continuing, and pack ice is drifting towards the Pole. The second is a lot more worrying in its implication.
If you go back to the NSIDC illustration of the season’s ice movement, there’s a strong pattern of motion across the North of Greenland and around the corner, into the Greenland Sea. Using CT’s large file of satellite images, or the NSIDC image, a lot of this looks like multi-season (old) pack ice being flushed out of the Arctic and into the North West Atlantic.
All of this means that it is possible that we may have already seen the minimum ice area day pass. I’d expect, though, to see a few more days of losses at least from that Kara/Laptev area, so there may yet be a slight dip before the thaw ends and the refreeze proper begins.
This Winter, then, the sea ice area will go back to its larger value. How much the maximum will be is dependent on a lot of factors, but a recovery to near-average maximum seems less than likely as things stand. And much more of the Winter ice will be first-year ice. Vulnerable ice. Even if the Winter was to see a return to nearer-normal average areas, the picture for next Spring’s melt season looks ominous already. Unless another major variable comes into play, and suppresses the sub-Arctic SST anomaly, reduces the Bering inflow, or cools the whole region by a few degrees compared to the past six years, then ice loss will be rapid and comprehensive early in the season.
It is not clear what impact this will have on the Northern Hemisphere’s climate or weather, nor what the feedback effect is likely to be. I can’t see that it’s likely to be good for us.
All of this is pure speculation. Unless it happens.
The NSIDC press release for the 4th September charts the continuing decline of Arctic sea ice, showing the August mean extent historical series, with 2007 dropping like a stone towards the bottom of the graph. “Don’t care,” is the response of some, “look at the trend for the Antarctic; it’s going up. It’s just natural variations.”
There are a lot of reasons why this idea is wrong-headed, but it gave the old man a thought.
How much sea ice is there at both poles put together? Is there any observable trend in the dual-hemisphere sea ice extent?
Doing a full time series for every month since 1979 (the satellite era) would take ages, so is there a shortcut? September and March are the two months where the sea ice generally reaches its respective maximum and minimum mean monthly extent in both hemispheres (how’s that for alliteration?) .
So I have extracted the mean monthly sea ice extent for these two months, for 1979-2006, from the NSIDC’s readily available dataset. Adding the NH and SH means together gives us a ‘global’ mean monthly extent, at the periods when the metric reaches its extremes at both poles (nominally). Then I summed the two separate months. Note here that there is more ice around in September (24-27 million km2) than there is in March (17.9-21 Mkm2). Also note that the range is greater in the SH than the NH.
(Sorry about the clumsy link; I can’t get the graphics insert sorted)
Oh. This was a bit of a surprise. I actually expected there to be little or no observable trend. But there is one. The trend is noticeably downwards.
All of this is an exercise in playing with the numbers, of course, but it should put one idea to bed: even though the sea ice measurements in the Antarctic show a small positive anomaly in the modern record, it is not enough to offset the large negative anomaly in the Arctic. Put simply; globally, there appears to be less ice than there used to be. Now why would that be?