This is the polar bear capital of the world, but the snow has gone

Canada's Hudson Bay is as ice-free in November as on a summer's day and polar bears could be extinct here by mid-century. If the bears are in trouble, so are we

Churchill, on the banks of the Hudson Bay in Canada, is known as the polar bear capital of the world. Hundreds of bears gather there each year before the sea freezes over in October and November so they can hunt seals again from the ice for the first time since the summer.

I first went there 12 years ago at this time of year. The place was white, the temperature was -20C, and the bears were out feeding.