Despite the US president's stance on climate change, his government last week took the first steps towards officially listing the bear as endangered, because the Arctic ice on which it lives is melting. If the listing is finalised, the Bush administration will be obliged under US law to modify its pollution policies to try to save the iconic animal.

The president has come under attack for the first time on global warming from some of his strongest allies, evangelical Christian leaders, who last week took out TV ads urging action. British prime minister Tony Blair also warned that the world had less than seven years to get to grips with climate change.

On Tuesday, the US Fish and Wildlife Service started the process of listing the bear in response to a law suit by environmental groups to get government protection for the species. It said the groups presented "substantial scientific and commercial information indicating that listing the polar bear may be warranted".

The bears are particularly vulnerable to climate change, as they depend entirely on polar ice to catch seals, their main prey. The seals swim too fast for them in open water, so they have to lie in wait for them to surface for air through holes and cracks in the ice.

The seals congregate in the shallow waters of the continental shelves, and the bears can reach them only when the sea is frozen. But the ice is now receding far out to sea every summer.

A new report by the United Nations Environment Programme, published at the annual meeting of its governing body in Dubai last week, concludes that the extent of summer ice in the Arctic has shrunk by more than a quarter in the last half-century. The US government's National Snow and Ice Data Centre adds that the past four years have all witnessed a "stunning" reduction in sea ice: last summer an area twice the size of Texas disappeared, and the ice receded 160 miles from the Alaskan coast.

The centre believes the rate of retreat is accelerating. Even worse for the bears, the melting is beginning earlier, depriving them of seals in the spring, when they have always stocked up on food to see them through the summer.

In desperation, more and more polar bears are swimming to land and marauding through villages. Made fearless by hunger, the half-ton animals roam through rubbish dumps and have even broken into houses in search of food.

One has already killed a 15year-old girl in the Russian Arctic, while children in the Canadian town of Churchill are taken to school under guard. There is even some evidence from northeast Russia that polar bears have taken to eating their own species.

The US Fish and Wildlife Service will gather evidence on the bears for the next two months before coming to a decision at the end of the year.

If the bear is listed, regulatory agencies would be bound by law to take into account how their decisions would affect it . . . which could lead to tougher measures on the pollution that causes global warming.