​The polar bear capital of the world

A walk among polar bears 09:44

Appreciating one of our continent's most remarkable creatures requires a little North exposure. Our Cover Story is reported by Lee Cowan:

On the edge of Canada's Arctic, along the western shore of Hudson Bay, it's easy to think you've reached the ends of the Earth. It can feel like you're utterly alone up here ... but then, out in all that white, a pair of sleepy, dark eyes slowly open -- revealing what we came all this way to see.

And apparently, the world's largest land predator came to see us, too.

"How rare is this to see here?" asked Cowan.

CBS News

"Well, it's pretty common to see polar bears out here this time of year," said scientist Steve Amstrup. "But it's not as common to see a big 'ol male like that just come and lay down right next to the buggy."

The buggy is a Tundra Buggy, sort of a cross between a tour bus and a monster truck. And it's where Amstrup does much of his work, as chief scientist for Polar Bears International, a private group campaigning for the bear's conservation.

"I've been working with polar bears for 35 years now, and I still, every time I see them, it's like, 'Holy cow, there's a real wild polar bear!' They're just incredible creatures."

We're near Churchill, Manitoba, a remote frontier town that proudly calls itself the "Polar Bear Capital of the World."

It is isolated, to be sure -- you can't even get to this town by road. But every Fall, these giants of the North come here in droves to wait for Hudson Bay to freeze back over so they can start eating again.

The polar bear's main source of food is seal meat, and the easiest way for the bears to hunt them is from the ice above.

As the chow line grows on land, another migration rolls up to watch ... a quiet stampede of eco-tourists anxious to catch a glimpse of an animal whose future is as hotly debated as climate change itself.

"In the United States, we have listed polar bears as a threatened species, under the U.S. Endangered Species Act," said Amstrup, "and they were listed as threatened not necessarily because of their current status, but because of what we anticipate their future status to be."

And what he anticipates their future status might be has Amstrup worried. But he knows not everyone is wringing their hands.

Currently, it's estimated there are between 20,000-25,000 polar bears in the wild.

To many, that's a pretty sizable number. And some of the bears -- especially in the upper reaches of the Arctic -- seem to be doing quite well.

But what concerns Amstrup the most are the bears here who, he says, are experiencing the effects of climate change right now.

"They lose about a kilogram of body weight -- about two pounds -- for every day they're on land," he said. "These guys are on land now a whole month longer than they were just 30 years ago.

"We could say, 'Well, yeah, one population might be doing well now,' but we know that soon, all of the populations will have less sea ice than they do now. Some of them will have NO sea ice."

Those who track sea ice levels, like the National Snow & Ice Data Center, say the seasonal ice here in the southernmost region of the polar bear's habitat is already melting earlier and freezing later. That means bears are marooned on land longer -- and getting hungrier.

"They came ashore this year, I think, around the middle of July. So he really hasn't had much to eat since then," Amstrup said.

In November, when we were there, the bears were spending their time lounging about, trying to conserve energy (which makes them pretty easy to find and photograph). Nothing makes for a better photo-op than a scratching, relaxing polar bear.

While they look as friendly as they are fuzzy, truth is they are one of nature's perfect killing machines. Their enormous size and strength are part of the allure.