two-thirds of the world’s polar bears — including all of those in Alaska and most of Canada’s western Arctic — will be gone by 2050. The only ones remaining, the panel warned, will be those animals inhabiting the High Arctic regions of Canada and western Greenland.

That opinion was given by the U.S. Geological Survey in a report a little more than a year ago according to an article recently reporting that more polar bears are now going hungry than they were two decades ago.

Care has to be taken about what conclusions can be drawn from the evidence. Apparently the study found that “nearly a third of the bears sampled were going without food longer than they normally would.” But this was in only one area – the Beaufort Sea which is located just north of the border between Alaska and Canada in the western Arctic.

Some visuals may help. This is the map of the Beaufort Sea:

This image shows how the ice is increasingly moving away from the coast in the western Arctic:

Those lines of course represent the maximum summer sea ice loss, usually in early autumn about mid-September. But this article puts the problem succinctly. As the years pass Arctic ice is melting earlier and forming later so that:

polar bears are left with less time on the ice to hunt for food and build up their fat stores, and increased time on land where they must fast. As their ice habitat shrinks, skinnier and hungrier polar bears face a grave challenge to their survival.

The loss of prime feeding time in the late summer and autumn is a particular issue for the female bears. In November-December they build an ice cave, give birth and then feed their young with milk generated by stored fat, emerging from the den in March-April.

The New Scientist picked up the story as a news item followed rapidly by an article by William Laurance suggesting that:

much greater danger is faced by the thousands of species – including many large, photogenic mammals – living in tropical rainforests.

He then mentions the “white lemuroid possum (Hemibelideus lemuroides), a striking animal confined to a cool mountain top in north Queensland” which no-one has seen for three years.

I think it’s a case of both/and rather than either/or.

This article by Ed Struzik explains how difficult it is to keep tabs on polar bears who have a range of up to “200,000 square kilometres” (sic) and have been known to swim 100 kilometres in 24 hours. Yet it seems clear that five of the 13 polar bear populations are declining in numbers, while only three populations are increasing. And two of those three are increasing because the Inuit have decided to decrease their hunting take.

The U.S. Geological Survey report cited at the top of the post used conservative, indeed optimistic projections of ice loss. Jo Romm at Climate Progress thinks the polar bears could be in real trouble by 2020 or 2030.

Another problem is that the staple diet of polar bears, the ringed seals, could be in trouble “because they need stable ice cover to nurse their pups in spring.” Remember that the white ice sheet in the image above includes all sea with a 15% or greater ice coverage. And that ice is becoming desperately thin. As Dr. Derocher says “no habitat, no seals; no seals, no bears.”

There is perhaps comfort in the fact that the polar bear has already survived one interglacial, the Eemian about 125kya, having evolved from the brown bear perhaps 200,000 years ago.

As against that it seems likely that the polar bear was not as specialised in terms of habitat then compared with now.

If we want to think short term, summer ice could clear from the Arctic as early as 2012.

We desperately need also to think long term, however, and Hansen has cautioned us that if CO2 levels persist at current levels for long enough we are likely to cop a temperature rise (from pre-industrial) of 2.7 to 3.7C and a sea level of 15 to 35m.

I’m afraid that with policy makers sprouting 450ppm and +2C as the guard rail but not taking actions that would bring us within a bulls roar of those inexcusably reckless targets I’ll have to keep posting on these matters while I have strength.

There’s more at Wikipedia whence come this depressing graphic:

For orientation, the Beaufort see is at the bottom while Greenland sticks out on the right side.

And here, also from Wiki, is the obligatory polar bear image:

It carries the caption:

Cubs are born helpless, and typically nurse for two and a half years.

Thankfully for mum bear, the wolves get some, but you can see that the mother bear has to do a lot of feeding in a very short time when she gets the chance.