Polar bears are creatures of paradox. They are white bears whose skin is black, massive predators that can walk almost silently, Arctic residents whose major problem is not staying warm, but keeping cool. Fully grown they can measure ten feet in length and close to 2,000 pounds, but at birth they weigh just twenty ounces. Creatures that may wander thousands of miles over the course of a year, they begin life in a snowdrift. The world's largest land carnivores, they are officially classified as marine mammals. But they are, above all, incontrovertibly, creatures of the ice. Without sea ice and the life it supports, polar bears cannot survive. According to scientific predictions, if warming continues at its present pace, summer sea ice could disappear entirely from the Arctic Ocean by the year 2040. If that happens, the polar bear - one of the most recognisable animals on the planet - could be extinct within a generation.
