It's March and I'm in the great white north. The snow around us is blown into a giant cloud

as the helicopter I'm crammed into lifts off. The pilot and the researcher I'm with decide

on the flight plan. We're heading out to Cape Churchill right

on the western edge of Hudson Bay in the northern part of the Canadian province of Manitoba.

This is the sub-Arctic where Boreal Forest meets Tundra, South touches north and where

sea ice meets land. Despite the hostile Arctic scene, we're actually nearly 500 miles south

of the Arctic Circle, but it feels Arctic in every way because of the chilling effect of

Hudson Bay, a massive body of water, the size of Texas. And at this time of year, it's still

frozen solid and home to hunting polar bears. The icy shapes are an incredible scene to take in.

It's approaching spring and most of the polar bears in this population are below me on the ice,

catching and eating as many seals as they can, quickly put an on fat before the bay melts in

the summer and the seals disappear with it. This sea ice of Hudson Bay is what makes life possible

here for polar bears. It's as important to them as the air they breathe. I mean polar bears,

their whole life history is evolved around sea ice. Everything they do is focused on the sea ice

and that's where they hunt seals, that's how they put on all their weight. Dr Nick Lund is a veteran

polar bear biologist I've come to visit here. For the last 42 years, he's been studying this

population of Hudson Bay polar bears and the impacts of climate change on the sub-Arctic.

We've all seen it, the image of a polar bear sitting on a slowly melting chunk of ice.

It's almost become a cliche. It's that unseen thing happening in some place far, far away.

But here it is very real for every individual polar bear. Every year, hundreds of bears move through

this area and they're forced to come ashore in the summer when the ice melts. A grueling annual

migration that pushes the bears from ice to land and back to ice again. But people live here too

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