Friday, February 11, 2011


February 10, 2011, 7:46 am

Requiem for the Bears?

A mother polar bear, left, with a tracking collar and her cub on the edge of Hudson Bay in Canada.

Agence France-Presse — Getty Images A mother polar bear, with tracking collar, and her cub on the edge of Hudson Bay in Canada.

Green: Science

In a recent article, I wrote about the unusual weather patterns of the last two winters, with excessive cold and snow in the eastern United States and western Europe occurring at the same time as unusual warmth in parts of the Arctic. One thing I did not mention in that story was what the likely effect on Arctic wildlife would be if this sort of thing continues.

A new study offers an ominous forecast for one flagship Arctic species, the polar bear. Bears in some parts of the far north are under increasing stress because of climate change. These bears do most of their feeding during the winter as they venture onto the sea ice to catch seals. But with the ongoing decline of that ice in recent decades, life has gotten harder for many of the bears.

Consider, for example, the polar bears of western Hudson Bay, in Canada. Earlier breakup of the Hudson Bay ice, evidently caused by global warming, is forcing the bears ashore sooner than in the past, and the late arrival of cold weather is delaying their return to the ice in the fall. This winter has been particularly bad — parts of Hudson Bay were still open water well into January, a highly unusual situation.

Scientists won’t know the exact effects of this year’s weather on the Hudson Bay bears until they do surveys in the summer. But past work shows that the bears are getting less time on the ice to fatten up, which means they are coming ashore with less energy stored up for the difficult summer months. “On shore, there is no food available for them,” said Peter K. Molnar, a researcher at Princeton and lead author of the new study.

Among the bears coming ashore with less fat are females of reproductive age. Some evidence suggests that the sizes of polar bear litters are declining already. The new study essentially predicts that this will continue, and that some female bears will not have enough stored energy to reproduce at all.

That means fewer bears will be born and have a chance to reach adulthood. Although some bear populations elsewhere in the Arctic are faring better, the western Hudson Bay population has already declined by more than 20 percent since the 1980s, so the new study adds fresh information to a bleak outlook.

Andrew Derocher of the University of Alberta, a co-author of the new paper, told me recently by e-mail: “It is likely that the long ice-free period of 2010 affected cubs born in both 2009 and 2010 and may have negative effects on females that were pregnant and gave birth to cubs in December.”

His colleague Ian Stirling, also at the University of Alberta, told me that the climate changes under way in the Arctic have so much momentum that even an immediate shift in global policy on emissions would likely come too late for this particular bear population. “I don’t think things look good for the bears of Hudson Bay in the next 20-30 years, even if we are able to stop anthropogenic warming, which presently appears very unlikely,” he wrote via e-mail.

Dr. Derocher pointed me toward this video of a skinny mother polar bear and her starving cubs, typical of the sort of thing likely to happen more often in the future. Warning: it is hard to watch.

A Warming Climate Takes its Toll on the Polar Bears of Hudson Bay. from Daniel J. Cox on Vimeo.