Top experts who gathered this week in Tromsoe in northern Norway to discuss ways of protecting the species sounded alarm bells over the dramatic consequences of the melting ice.

"We don't have hard evidence about climate change but we have evidence about the numerous symptoms of climate change on polar bears," Andrew Derocher, chair of the Polar Bear Specialist Group, an international network of researchers, said.

The primary observation is that as the sea ice shrinks away, so are the polar bears -- they're not growing as big as they used to.

In Canada's Hudson Bay, home to a large polar bear population, the ice season is now three weeks shorter than it was 30 years ago, chipping away at the bears' opportunity to hunt seals, their primary source of food and an essential source of fat needed for their long summer fast.

Females today weigh around 230 kilos (500 pounds), some 65 kilos less than in 1980, and measure about 185 centimetres (6.07 feet) on average, compared to around 220 centimetres a few decades ago.

The melting ice means not only shorter hunting seasons, but it also means the bears, who number some 20,000 to 25,000 worldwide, have to cross greater distances to reach their icy hunting grounds.

This has led to a deterioration of the bears' health, impacting their reproductive capacities and the cubs' chances of survival, experts warned.

"The chain of events starts with a drop in body condition that subsequently leads to a drop in reproduction which leads to a drop in survival," Derocher said.

Climate change also appears to have altered the bears' behavioural patterns.

Several recent incidents of cannibalism in Alaska have observers worried.

"We knew of polar bears killing and eating other polar bears," Steven Amstrup, a research wildlife biologist with the US Geological Survey, told AFP.

"But the difference was that this time the polar bears were clearly deliberately hunting other bears, attacking for example females in their denning area" in northern Alaska, he said.

"We assume that it was linked to nutritional stress."

Faced with the growing uncertainty concerning the ice, pregnant polar bears are increasingly denning on land, researchers have noticed.

In northern Alaska, two-thirds of bears now choose to den on land in order to give birth early in the year, an inverse proportion of what was observed a few years ago.

"They are refugees rather than immigrants. This is not a chosen exile, this is a forced exile," Derocher told AFP.

The shrinking sea ice is also sometimes forcing the bears to swim ever further afield, encountering more treacherous waters.

Polar bears are accomplished swimmers -- their Latin name is ursus maritimus -- yet in late 2004, four polar bears were found dead after drowning in the Beaufort Sea north of Alaska, likely the victims of a heavy sea.

According to scientists' estimates, some 25 polar bears may have died in that incident.

"Any of these symptoms taken alone might not be so worrying but seen in their totality it shows a bleak picture of how climate change is impacting polar bears already now," said Geoff York, a polar bear expert at environmental group WWF.

"And it's only forecast to get worse," he said.

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