We’ve hit the seasonal Arctic sea ice minimum for this year, called this morning by US NSIDC for 19th and 23rd of Septmeber: 4.59 mkm2, the same extent as 2008 and 2010. This is not a “ho-hum” year for polar bears: it means that since 2007, they have triumphed through 10 or 11 years1 with summer ice coverage below 5.0 mkm2 — levels that in 2007were expected to cause catastrophic declines in numbers.
Summer sea ice below 5.0 mkm2 were not expected to occur until about 2050, according to 2005/2006 sea ice models and polar bear specialists at the US Geological Survey (USGS). Polar bear survival models predicted 2/3 of the world’s polar bears would disappear when ice levels reached this threshold for 8 out of 10 years (Amstrup et al. 2007, 2008; Hunter 2007) but polar bears have been more resilientthan expected (Crockford 2017, 2018; Crockford…
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