Climate threat to polar bears: despite facts, doubters remain

Those facts are incontrovertible. So is the fact that over tens of thousands of years, polar bears have evolved to spend most of their lives - and do nearly all of their hunting for their favoured prey, ringed seals - on sea ice. This is especially true in spring, when the bears fatten up on seals so the female polar bears can put on sufficient calories to gestate and nurse cubs. Not only is Arctic sea ice declining overall, but it is breaking up earlier in spring; in some regions - such as western Hudson Bay - sea ice has been melting three weeks earlier than in the mid-1980s, depriving polar bears of a vital feeding opportunity.

Over the past two decades, studies in western and southern Hudson Bay show that polar bears are growing thinner, that undernourished females are having smaller litters, and that females are giving birth to lighter cubs that do not survive as well.

Stirling and Steve Amstrup, a US Geological Survey polar bear biologist who headed the blue-ribbon study panel, have seen telltale signs that polar bears are also in trouble in the southern Beaufort Sea. In Alaska especially, polar bears are increasingly likely to den on land rather than on the sea ice because the ice is not as stable a denning platform as it once was. Furthermore, increasing numbers of polar bears have been seen hundreds of miles inland or swimming far offshore.

The latest authoritative estimate on the health of polar bear populations comes from the Polar Bear Specialist Group at the International Union for Conservation of Nature (IUCN). The group reported in early July that eight of the Arctic’s 19 polar bear subpopulations are in decline. In western Hudson Bay, for example, populations have fallen from roughly 1,200 to 1,000 in the past two decades. Three subpopulations are stable and one is believed to be increasing, the Polar Bear Specialist Group reported. No good data exists on the remaining seven subpopulations.

Some of the contrarian views on polar bears started off innocently enough. In the journal Polar Biology, for example, ornithologist Robert Rockwell and graduate student Linda Gormezano, both associated with the American Museum of Natural History and City University of New York, suggested that polar bears on the west coast of Hudson Bay - which now spend as much as five months fasting on land in summer and fall - might find relief in the future by turning their attention to snow goose eggs. The study evolved out of Rockwell’s decades-long work on snow geese in Hudson Bay.

The snow goose specialists aren’t alone in suggesting that polar bears could adapt to life on land. In the current issue of The Journal of Mammalogy, Markus G. Dyck, an instructor at Nunavut College in Iqaluit, and Ermias Kebreab, an associate professor at the University of Manitoba, suggest that if sufficient berries are available on land, they could possibly replace calories the bears lose from eating fewer seals at sea. Dyck and Kebreab predict that polar bears will adapt if sea ice continues to decline.

But polar bear researchers say it is highly unlikely that goose eggs and berries would ever be able to replace the trove of calories the bears now ingest from eating fatty seals. Andrew Derocher, chairman of IUCN's Polar Bear Specialist Group, has written a soon-to-be published paper with an associate demonstrating that there are simply not enough resources on land - be they goose eggs, kelp, or berries - to replace what the bears get on the ice.

“A few good feedings of goose eggs will pretty much wipe out that resource,” said Derocher, who has worked on polar bears in Svalbard, the Beaufort Sea, Hudson Bay, and Wager Bay in northern Canada. “In the long run, goose eggs can contribute nothing of energetic consequence to polar bears.”

Even the snow geese scientists concede that in 40 years, only six bears - four since 2000 - have been seen feeding on snow goose eggs. In addition, Derocher and Stirling have shown that polar bears lose about a kilogram per day when they are stuck on land. Those periods of food deprivation on land have become prolonged in recent years, but still the bears have not turned to goose eggs or berries for sustenance.

“If polar bears could offset that weight loss and its associated population impacts by taking eggs or other supplemental food they would be doing so now,” said Amstrup.

Another global warming sceptic who has joined the polar bear debate is J. Scott Armstrong, a marketing professor at the Wharton School at the University of Pennsylvania who specialises in forecasting methods. He has made numerous statements in the media and to Congress casting doubt on global warming and its threat to polar bears. Armstrong insists that models used by climatologists to forecast the future of the polar bear in an increasingly ice-free Arctic are worthless. He also maintains that the Earth currently has as much chance of cooling as it does of warming - a statement contradicted by the overwhelming majority of the world’s climate scientists.

The Alaskan government has signed a contract with Armstrong to provide justification for the state’s opposition to the listing of polar bears as a threatened species, despite Armstrong’s lack of scientific credentials.