February 20, 2004
While it has been known for some time that the polar bear is in trouble, new research shows that Arctic ice--the polar bear's primary habitat--is melting much faster than scientists had believed, says U of A biologist Dr. Andrew Derocher.
"The climate predictions coming out are showing massive changes in sea-ice distribution," said Derocher, who follows polar bears to see how they adapt to changing conditions. If the predictions are correct, he says, "we'll certainly lose polar bears in a lot of areas where we currently have them." Ice conditions in the Beaufort Sea, for example, are already changing dramatically.
The world's largest terrestrial carnivores, polar bears rely on sea ice to survive, using it to pass between forest dens and hunting grounds where they prey on seals. There are about 15,000 polar bears in northern Canada, accounting for about two-thirds of the world's total population.
Derocher shared his views Jan. 6 at a symposium on Arctic biology in Toronto. It was the biggest gathering of Canadian Arctic biologists in more than a decade, says co-chair Dr. David Hik, also of the U of A. Many of the talks addressed the impact of climate change on northern ecosystems.
Derocher says if global warming continues unchecked, some remnant populations of polar bears may manage to hang on in the high Canadian archipelago or on permanent polar ice at very high latitudes. But the potential for extinction is still a cause for concern: "You don't have to be a polar scientist to see that if you take away all the sea ice, you don't have polar bears any more."
To make matters worse, sea-ice melting is accelerated by "positive feedback loops." Sea ice acts as a reflector of solar energy, but when the ice disappears, the ocean absorbs that heat energy, which in turn prevents ice from freezing.
"Once climate warming initiates, you get into a self-warming cycle," said Derocher, who earned international renown as a polar bear and northern studies expert at the Norwegian Polar Institute in Tromso before returning to the University of Alberta, where he completed his doctorate. "That's why the urgency on the issue for polar bears now."
He adds that it is possible a warmer climate will improve polar bear and seal habitats in the short term, mainly in higher latitudes where ice is too thick for seal hunting. But these areas are small, he says, and will only support a fraction of the bear population.
Polar bears can tolerate some environmental variation from year to year, foregoing reproduction in any given year if conditions are poor." With too much variation, however, reproduction will fall off dramatically, and populations will quickly decline. Scientists have no evidence yet of a drop in polar bear populations, but body weights and reproductive rates of bears in the Hudson Bay are on the decline," said Derocher.
Hik says there is also new research looking at the harmful effect of drought-related forest fires on polar bear dens, which are built in mature forests.
"When you burn the forest down, it blackens the earth, and these dens burrowed into the permafrost collapse," said Hik. "Many of them are created over centuries by successive generations of bears scraping deeper and deeper in." The area around Churchill, Manitoba is one such area that has been losing these dens.
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