According to the National Snow and Ice Data Center (NSIDC, Sept. 20 report), the annual sea ice minimum extent was reached on Sept. 13, 2013.
At 5.10 million square kilometers, this year’s low was a whopping 1.69 million square kilometers above the minimum extent for 2012 (which was the lowest since 1979) and well within two standard deviations of the 1979-2010 average. (Two standard deviations: “Measurements that fall far outside of the two standard deviation range or consistently fall outside that range suggest that something unusual is occurring that can’t be explained by normal processes”).
The minimum extent for 2013 is virtually indistinguishable from the minimum for 2009, which was 5.13 million square kilometers. The ice was distributed a bit differently in 2009 – more in the east and less in the west — than it was this year (see Fig. 1 below).
Figure 1. I used JAXA to plot the date the 2013 minimum was reached (September 13, 5.10 million square kilometers, white) with an overlay (purple) for the same date back in 2009 (September 13, 2009, 5.13 million square kilometers), when that year’s minimum was reached. Areas of overlap are pink.
You’ll know from previous discussions here that the annual minimum reached in late summer has little impact on polar bear health and survival (see excellent summary of the evidence for that here). What matters most to polar bears is the presence of ample ice in spring and early summer (March-June), which is their critical feeding period.
But after the fast that many polar bears endure over the height of the summer, they are eager to get back onto the ice and resume hunting. When in the fall does that become possible?
I wondered what the similarity in extent for 2013 and 2009 might tell us about polar bear habitat development over the next month or so.
In other words, what might polar bears this year expect in the way of sea ice development by say, the end of October? When might they be able to start hunting?
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