The freeze is on: from an annual low of ~5.1 m sq km at 15 September 2014, the sea ice that provides a hunting platform for polar bears is rapidly reforming.
Note that polar bear habitat world-wide is pretty well defined by the extent of sea ice in spring, with three notable exceptions. There are no polar bears (or fossil evidence of polar bears), in the Sea of Okhotsk, the Gulf of St. Lawrence, or the Baltic Sea.
Bears in some areas spend time on land in late summer/early fall but the amount of time varies widely.
Have a look at the maps below: the difference in regional coverage between the sea ice at 4 August and 16 October (73 days apart, both covering 7.3 mkm2) might surprise you.
Evolution is not just for the long-term – natural selection also goes on over short time periods. In the case of polar bears, this adaptation is almost certainly critical for its long-term survival.
Hudson Bay female with cub Wapusk National Park, Thorsten Milse, Government of Canada
Not all polar bears are identical — that is the reality that allows natural selection to operate.
I will argue that early breakup years in Western Hudson Bay weed out individual polar bears that do not have the physiological or behavioral characteristics necessary to be useful members of the population – and that this is a good thing for the entire population.
Posted in Evolution, Population, Sea ice habitat
Tagged adaptation, declining sea ice, early breakup, evolution, historical sea ice record, indivdual variation, late freeze-up, natural selection, NSIDC, polar bear, resilience, sea ice minimum, sea ice variability, Stirling, Stroeve, survival, western hudson bay
I just came across the National Snow and Ice Data Center (NSIDC) “monthly highlights” article for April 2013 (Glimpses of sea ice past), which turned out to be a rather more interesting story than it appeared at first glance.
The article chronicles the details of how NSIDC technicians pieced together photos taken by the Nimbus 1 satellite between August 28 and September 23, 1964 – of both the Arctic and the Antarctic – to create an estimate of sea ice extent at September 1964 for both regions. For the Arctic, this was the yearly minimum; for the Antarctic, the yearly maximum.
NSIDC scientist Walt Meier was part of this effort and he and colleagues Gallaher and Campbell recently published their findings in the journal The Cryosphere (Meier et al. 2013). For the Arctic estimate, they had to add in data from Alaskan and Russian sea ice charts because the 1964 satellite data was not complete. This means the ice extent figure they came up with is not a true ‘satellite only’ figure but a composite one.
One of the things they did in their analysis was to place the 1964 value on a graph of the more recent 1979-2012 data, which really helps put it into perspective (see Fig. 1 below).
Figure 1. This is Fig. 7 from the Meier et al. 2013 paper, to which I’ve added labels. Meier et al. call this a “time series of Arctic September sea ice extent.” The estimate for 1964 is the red dot on the far left (with its error bars), which I’ve circled (I also added the red label for 1964 and the black line). Note the Y-axis on the left goes to 3.0 million km2, not zero. The solid blue line is the monthly average for September from passive microwave data (1979-2012), and the blue dashed lines are a “three-day average of the high and low range of daily extents during the month.” The 1964 estimate of 6.90 ± 0.3 million km2 is just about identical to 1979, 1981, and 2001 and well within the average for 1979-2000. However, Meier and colleagues note it is significantly lower than the previous estimate of 8.28 million km2 for 1964, made by the UK Hadley Centre in 2003.
Posted in History, Sea ice habitat
Tagged Antarctic sea ice, arctic sea ice, earliest satellite sea ice data, Eastern Beaufort, Hadley Centre, heavy sea ice, National Snow and Ice Data Center, Nimbus I, NSIDC, satellite data, sea ice extent, sea ice maximum, sea ice minimum, Walt Meier
As I mentioned here in an update to my March 7th post, Damian Carrington at the Guardian Environment blog had this telling quote about the CITES deliberations that took place prior to the vote to ban polar bear trade (by uplisting its status from Appendix II to Appendix I):
As the debate raged, national delegates from other countries got confused by the strident but conflicting claims. “Where is the truth? Is it true that the polar bear is declining. Is it true that trade is increasing? We need to know,” said the Egyptian delegate.[my bold]
Indeed. Was there “truth” in the presentations heard by delegates? By that I mean, honest presentations of facts so that delegates could make up their own minds, or facts loaded with spin to sway the decision one way or another? I wasn’t there so I can’t say. But we can get some impression of what might have been said from two
press releases statements issued after the vote failed by two parties that were actively promoting acceptance of the US-led proposal.[Update: Humane Society Press Release is here] Continue reading
Posted in Advocacy, Conservation Status, Population, Sea ice habitat
Tagged advocacy, Chukchi, CITES, Hudson Bay breakup, Humane Society, Polar Bear Specialist Group, sea ice extent, sea ice minimum, US Fish & Wildlife