The US Geological Survey is trying on the "polar bears are all going to die" line again, the latest in a long line of attempts to link polar bear populations to summer ice extent (predicted to decline rapidly under global warming) despite all the evidence pointing to spring ice thickness (little affected by small amounts of warming) being the critical factor. In fact it is thick ice that seems to be the problem, causing declines in populations of both seals and the polar bears that prey on them. Polar bears do most of their feeding in the spring, when seal pups are there for the taking; they tend to fast over the summer.

The USGS press release is interesting, revealing that the authors used IPCC models of sea ice extent and then tried to derive future polar bear populations from them (I kid you not). They conclude that all bear populations will decrease in the future except in one region "where sea ice generally persists longer in the summer". And confirming that they are quite clear that it's summer ice that is (allegedly) the issue, there is this:

Substantial sea ice loss and expected declines in the availability of marine prey that polar bears eat are the most important specific reasons for the increasingly worse outlook for polar bear populations,” said Todd Atwood, research biologist with the USGS, and lead author of the study

The problem is they are having trouble getting their story straight, since they allude directly to polar bears having limited access to seals in the summer:

USGS researchers noted that if the summer ice-free period lengthens beyond 4 months – as forecasted to occur during the last half of this century in the unabated scenario – the negative effects on polar bears will be more pronounced. Polar bears rely on ice as the platform for hunting their primary prey – ice seals – and when sea ice completely melts in summer, the bears must retreat to land where their access to seals is limited. Other research this year has shown that terrestrial foods available to polar bears during these land-bound months are unlikely to help polar bear populations adapt to sea ice loss.

That's right, polar bears already have limited access to food in the summer - the ice mostly melts now. It always has done, in living memory and beyond. That's why bears feed up in the spring, a process that will be helped, not hindered by thinner ice.

Atwood is a familar name to those following the great polar bear propaganda campaign. Here's a comment on his last paper from a recent GWPF report by Susan Crockford:

The complex ‘second generation’ model produced in 2014 by Atwood and colleagues assumes the only sea ice change that ‘threatens’ polar bear health or population size is the predicted decline in summer ice extent blamed on human-caused global warming. The well-documented variations in spring ice thickness in the Southern Beaufort, and their associated repercussions on seal and polar bear populations, have been glossed over in favor of spurious correlations with summer-ice declines.

No doubt Atwood and colleagues will keep trying though.