30 August SIO Update
A new SIO bar chart was added with contributions as of 10 September 2012
According to NSIDC, on or about 26 August the arctic sea ice extent surpassed the previous record from 2007 of 4.2 million square kilometers with a value of 4.0 million square kilometers, according to their algorithm. Today's value is 3.8 million square kilometers with nominally two more weeks to go for this year's ice season. The sea ice concentration plot from Cyrosphere Today is below; the red-orange region is ~60 % concentration.
The time series plot from NSIDC is below. Note the continued downward slope of the 2012 line, which is unusual for this time of year. We had two rapid periods of loss this summer—early June with an Arctic Dipole weather pattern and then in early August. Summer 2012 had unusual weather with spatially extensive regions of low sea level pressure. Several posts suggest that these winds helped to open up the pack ice. Consequently, this year sea ice hung around Alaska through July, then rapidly retreated on the large scale plots in the first two weeks of August, in contrast to previous years.
On 27 August we posted an announcement to the SIO mailing list for updates or subjective estimates for the daily minimum for September. Asking for a 'daily' minimum is different than the September monthly value that we normally compare against, so we got a mix of interpretations. In either case, below is the distribution graph of responses.
With the continuing downward slope of the NSIDC sea ice extent line, one might speculate that this year crossed some threshold of sea ice thickness that made it more vulnerable to complete local melting given the normal summer seasonal forcing. This may support the argument that one should look at the downward trend of sea ice volume rather than extent or area.
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Beitsch et al. (updated 4 September)