Interestingly, after a heated discussion calling into question the reasons for proponents of global warming and global warming skeptics say what they do in my last diary, the National Snow and Ice Data Center staff's ears must have been burning.
They've done a mid-month update explaining why the loss of sea ice has decreased markedly since late July; it turns out that it is the result of a change in Arctic circulation, that is keeping sea ice from exiting the Arctic Ocean basin through the Fram Strait.
More below the fold.
In 2007 and June-July 2009, there was a circulation favorable to ice leaving the Arctic through the Fram Strait, which is between Greenland and Svalbard, north of Scandinavia. During this period, high pressure had been centered north of AK with a ridge line extending eastward to northern Greenland, encouraging west-to-east, and then north winds that pushed ice southward east of Greenland.
In late July 2009, that high pressure area decayed and a new one developed in the Barents Sea northeast of Scandinavia, with low pressure in the Laptev Sea, resulting in the stoppage of ice moving south through the Fram Strait, but rather clockwise around the Barents Sea high pressure area toward the Arctic coast of Siberia (go to the bottom of the three panels for August 2009).
Ice moving south would obviously melt; ice moving toward the Arctic coast of Siberia would melt, but more slowly, since the water is colder there than the North Atlantic Drift Current. If the old circulation and the July 2009 melt rate had persisted, I suspect (and of course there's no way to know for sure) that we'd be talking about at least the 2d lowest sea ice minimum coming up in September. As it is, the current concentration is just above that of 2008 at this date.
We'll see whether or not this circulation persists. NSIDC now believes we will have more sea ice at minimum than 2007 and 2008. I think we'll still be a bit below 2005, which would put us at 3d lowest in the satellite record.
I'll analyze the 1870-2008 seasonal record and discuss how the time series was made in one or two diaries in the next week or two, as promised in last weekend's diary.