Friday, September 23, 2011

Sea Ice Minimum

Based on the National Snow and Ice Data Center analysis, it appears we have passed the sea-ice extent minimum for the 2011 calendar year, as the extent has increased over the past several days.

This year's minimum was just slightly higher than the record minimum for the satellite era, which was set in 2007.  Nevertheless, model estimates of total sea-ice volume from the Polar Science Center at the University of Washington, show this was a record low year when the total ice volume is considered (the analysis below removes the monthly mean, which helps take out the seasonal cycle).

If you are wondering how this compares with the pre-satellite era, there is a discussion of longer records of ice coverage in the IPCC fourth assessment report.  They concluded that there was a "clear indication of sustained decline in arctic ice extent since about the early 1970s, especially in summer" as can be seen in the time series of northern hemisphere sea-ice extent for September (red line below).

Source: Lemke et al. (2007)

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