Because the U.S. classifies the polar bear as a marine mammal, the rule means that the bear's new threatened status will not impact oil exploration within its habitat.
Subsistence harvesting of polar bears and interstate trade in native handicrafts made from the animals will also be allowed to continue.
However, the listing means that import of polar bear products from Canada—where trophy hunting is still legal—will now be banned.
Reactions to today's announcement were a mixed bag of elation and frustration.
Scott Bergen is a landscape ecologist with the New York-based Wildlife Conservation Society and a contributing author to a spate of U.S. Geological Survey studies released in 2007 that found two-thirds of the world's polar bears could go extinct by 2050.
He and other WCS staff are "almost elated" with the decision, he said.
"Even though it doesn't directly influence carbon emissions so to speak, we think it is a definite decision in the right direction and we're pleased to see the Fish and Wildlife Service is supporting the best science on this species," he added.
Kassie Siegel, climate program director with the Center for Biological Diversity in Joshua Tree, California, wrote the petition seeking U.S. protections for the polar bear.
"[The] listing is great news for the polar bear, there's no question about that," she said. "The Endangered Species Act provides broad and strong protection. I think it's a watershed moment."
However, she added, the Bush Administration's attempt to exempt regulation of greenhouse gases in plans to protect the polar bear is illegal and wrong.
"We will be continuing to fight for the full protections that the polar bear needs and deserves," she said.
In a telephone briefing with reporters prior to today's announcement, Margaret Williams of the global conservation organization WWF said ESA listing is an important tool in polar bear protections.
"The ESA listing will require that critical habitat be identified [and] that a recovery plan be put into place, and those are important steps forward," she said.
"However, the bottom line is that climate change and warming temperatures are changing the Arctic dramatically, and that is the overall issue we need to address."
Kempthorne noted that tackling global climate change and the melting Arctic sea ice requires the efforts all major economies in the world to be effective.
"That's why I'm taking administrative and regulatory action to make certain that the ESA isn't abused to make global warming policies," he said.
WCS' Bergen noted that saving the polar bear will hinge on international cooperation.
Permanent sea-ice habitat is likely to remain in areas outside of the U.S., particularly in Canada and Greenland.
Scientists view these slices of habitat as refuges that could allow some polar bear populations to survive over the long term and repopulate the Arctic if temperatures decrease and sea ice returns.
"If you take a long-term view—meaning a hundred-year view into the future," he said, "polar bears' existence is not necessarily totally dependent on what happens in the United States."
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