The Interior Department proposed Wednesday to designate polar bears as a threatened species, saying that the accelerating loss of the Arctic ice that is the bears' hunting platform. has led biologists to believe that bear populations will decline, perhaps sharply, in the coming decades.

Many experts on the Arctic say that global warming is causing the ice to melt and that the warming is at least partly the result of the atmospheric buildup of heat-trapping gases from tailpipes and smokestacks. The plight of the polar bear has been held up by environmentalists as a symbol of global warming caused by humans.

But in a conference call with reporters, Interior Secretary Dirk Kempthorne said that although his decision to seek protection for polar bears acknowledged the melting of the Arctic ice, his department was not taking a position on why the ice was melting or what to do about it.

While the Bush administration "takes climate change very seriously and recognizes the role of greenhouse gases in climate change", Mr. Kempthorne said, it was not his department's job to assess causes or prescribe solutions. "That whole aspect of climate change is beyond the scope of the Endangered Species Act," he added..

The scientific analysis in the proposal itself, however, did assess the cause of melting ice. Most of the studies on the Arctic climate and ice trends cited to support the proposed listing assumed that the buildup of heat-trapping gases was probably contributing to the loss of sea ice, or that the continued buildup of these gases, left unchecked, could create ice-free Arctic summers later this century, and possibly in as little as three decades.

The Interior Department has a year to gather and study comments on the proposed listing and make a final determination. It must also work out a recovery plan to control and reduce harmful impacts to the species, usually by controlling the activities that cause harm. It is unclear whether such a recovery plan could avoid addressing the link between manmade emissions of heat- trapping gases and the increase in Arctic temperatures.

Kerr Davies, the research director for Greenpeace U.S.A., one of three environmental groups that sued the Interior Department in 2005 to force it to add polar bears to the list of threatened species, said the administration was "clearly scrambling for credibility of any kind in this issue."

Kassie Siegel, the lawyer for the Center for Biological Diversity, a group based in Arizona that took the lead in the lawsuit calling on the department to list the polar bear, added, "I don't see how even this administration can write this proposal without acknowledging that the primary threat to polar bears is global warming and without acknowledging the science of global warming."

As a result of the lawsuit, the Interior Department had a court-ordered deadline of Wednesday to make a decision.

Many experts hold that the forthcoming decline of polar bears is______.

A．directly caused by the diminishing Arctic ice

B．directly caused by the atmospheric buildup of heat-trapping gases

C．a symbol of the weather change

D．absolutely based on the emission of heat-trapping gases