Feeling the heat: Polar bear in Wager Bay off Nunavut, Canada. Bears are usually good swimmers but melting sea ice is forcing them to swim further than ever before.

Credit: Wikimedia/Ansgar Walk

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TROMSOE: Potentially fatal to the polar bear, global warming has already left its mark on the species with smaller, less robust bears increasingly showing cannibalistic tendencies.

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.

Hudson Bay

"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 kg, some 65 kg less than in 1980, and measure about 185 cm on average, compared to around 220 cm a few decades ago.

Shorter hunting seasons

The melting ice means not only shorter hunting seasons, but it also means the bears, which 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," said Steven Amstrup, a research wildlife biologist with the U.S. Geological Survey.