A polar bear cub nuzzles its mother in Wapusk National Park on the shore of Hudson Bay near Churchill, Man., Nov. 4, 2007. (Jonathan Hayward/Canadian Press)

The U.S. government has decided to list polar bears as a threatened species under its Endangered Species Act because of the effects of global warming — a decision lauded by wildlife groups, but that could deal a severe blow to the lucrative sport hunt in Canada's North.

U.S. Secretary of the Interior Dirk Kempthorne, who made the announcement in Washington on Wednesday, said the decision was based on findings that polar bears' sea ice habitat, vital to their survival, has dramatically melted in recent decades.

He said computer models projected declines in sea ice averaging 30 per cent by the middle of the century. Scientists predict that as a result, two-thirds of polar bears could disappear by then.

“Because polar bears are vulnerable to this loss of habitat, they are, in my judgment, likely to become endangered in the foreseeable future. In this case, [in] 45 years," Kempthorne said.

A threatened species is considered likely to become in danger of extinction in the foreseeable future.

Several U.S. activist groups, including Greenpeace and the Center for Biological Diversity, have been lobbying hard to have polar bears listed as threatened.

'Very good news for polar bears'

Experts believe there are as many as 25,000 polar bears remaining in the world, and that number is declining.

"He's made the right decision here," Peter Ewins, director of species conservation with World Wildlife Fund Canada, told CBC News in an interview.

"This is very good news for polar bears, and it's a first step towards turning this problem around. It's to be congratulated."

Listing the polar bear as a threatened species means all U.S. federal agencies will have to ensure that anything they authorize that might affect polar bears will not jeopardize the bears' survival or the sea ice where they live. That could include oil and gas exploration, commercial shipping, or even releases of toxic contaminants or climate-affecting pollution.

But Kempthorne stressed the loss of sea ice, and not oil and gas development, is the reason the bears are threatened.

He said that according to the Fish and Wildlife Service, no polar bears have been killed due to encounters associated with oil and gas operations in the Arctic.

He cautioned that the Endangered Species Act should not be used to regulate greenhouse gas emissions from automobiles, power plants and other sources.

"That would be a wholly inappropriate use of the Endangered Species Act. ESA is not the right tool to set U.S. climate policy."

Wednesday's decision will also impact Inuit hunters, especially in Nunavut, who profit from U.S. hunters coming north for trophy hunts for bears. The industry can net Inuit guides thousands of dollars per hunt.

The Nunavut government opposed listing the species as threatened, as politicians fear it could lead to a ban on the import of trophy bear hunts and potentially bar American sport hunters from bringing the hides of the animals back home with them, severely limiting the appeal of the hunt.

Bears may go beyond 'special concern': Baird

Polar bears have been a species "of special concern" in Canada since 1991 — one step below "threatened" and two steps down from "endangered." Last month, the scientific committee that evaluates species at risk recommended that the federal government retain the "special concern" designation for the polar bear.

Environment Minister John Baird said polar bears will keep that listing for now, but may consider changing the status for selected bear populations in some parts of the Canadian Arctic.

His department is holding consulations with Inuit and scientists on the issue, he added.

"Obviously the situations are very different in each of the sub-populations," Baird told reporters in Ottawa on Wednesday afternoon.

"That's why we're waiting for the detailed science, and we may have to take more agressive action to deal with some sub-populations than others."

Earlier this year, Baird said that Canada will not necessarily follow the lead of the U.S., but some scientists have said it would be difficult for Canada to justify not giving polar bears a similar designation.

Kempthorne said that just last week, he had signed a memorandum of understanding with Baird to work together on shared polar bear populations in the Beaufort Sea.