Russia's polar bears are adapting their behaviour to overcome the "catastrophic effects" of global warming, but new migration routes are pushing them dangerously close to humans, a leading researcher said. The polar bear population that stretches from eastern Russia to the US state of Alaska has fallen from an estimated 4,000 to around 1,500 as ice fields melted in the past 20 years, said Nikita Ovsyanikov, the top polar bear expert at the Academy of Sciences.

But growing temperatures have also opened up some new feeding grounds by allowing the bears to break through the ice, he said, forcing the great white carnivores closer to human settlements where they are often killed by nervous residents and poachers.

"What we are seeing is likely a model of how they have survived such periods of warming in the past, the sea is changing, their food sources are changing, but alternative resources are appearing," said Ms Ovsyanikov.

Environmentalist groups say that the up to four degrees Celsius rise felt across parts of the Arctic in the last 30 years is due to human activity and carbon emissions.

"Of course some populations may die out completely, and some will shrink drastically, but some will survive," Ms Osyanikov said. Polar bears' survival depends on catching seals on ice, but Arctic sea ice is shrinking fast: in 2007, it shrank to its smallest since satellite measurements began 30 years ago, raising the prospect that it could vanish in summers. Video footage shot by Ms Ovsyanikov showed a bear crashing through ice and slowly pulling himself back up with his front paws before crashing through again. Another shows a bear being attacked by two dogs as he searches for food near a human settlement.