This makes the mighty polar bear the first animal to be listed as endangered or threatened as a result of global warming.

In Canada, polar bears are listed as a species of "special concern." At the moment, Canada has no plans to change the designation, but Wednesday's U.S. move might put more pressure on Environment Minister John Baird to move further on the matter.

Dirk Kempthorne, the U.S. Interior Secretary, said he ordered a geological survey that shows even less sea ice this year than earlier models had predicted.

The expected decline in Arctic sea ice could wipe out two-thirds of the polar bear population by 2050.

There are an estimated 25,000 polar bears in the Arctic, many of them in the 30 million acres of the Alaska's Chukchi Sea, which is due to be auctioned for oil and gas exploration.

The World Wildlife Federation and other environmentalists have been lobbying the U.S. Fish and Wildlife Service (FWS) to add polar bears to the Endangered Species Act ahead of that auction.

The U.S. Interior's report on polar bears says that since the signing of the 1973 Polar Bear Agreement between Canada, Russia, Denmark, Norway and the U.S., the documented impact of the oil and gas industry on the animal has been "minimal."

However, the report acknowledges that as gas and oil operations increase, as does the possibility of an oil spill. The report says the probability of an oil spill is low but could have major effects on polar bears and their prey in the region of the spill.

The U.S. government has argued that closing the Chukchi Sea to oil and gas exploration would lead to higher fuel prices.

The decision on polar bears comes just a day before U.S. court-imposed deadline on the issue.

Polar bears in Canada

More than half of the worldwide polar bear population is within Canada.

Rachel Plotkin, a biodiversity policy analyst with the David Suzuki Foundation told CTV Newsnet that there has been a lot of debate in the scientific community over whether or not the polar bear population has been actually increasing recently.

She said the scientific consensus is that "while in the short-term, climate change might create some favourable conditions, polar bears depend on sea ice and sea ice is disappearing."

"There's a wipespread recognition that the fate of the polar bears is not looking good unless significant changes to our greenhouse gas emissions are made."

The Suzuki Foundation is calling upon the Harper government to list the polar bear as an at-risk species.'