The Alaskan sea ice

"An increase of about two degrees (Celsius) can mean as much as another month of open water," he said. No-one knows if the trend will continue.

If it does, the Arctic Ocean could be completely free of summer ice towards the end of this century. That could devastate the wildlife that relies on it for hunting, breeding, and protection from shipping.

But for now, though, some species are positively booming. The polar bear population on Alaska's coast has doubled since the '70s, thanks largely to a hunting ban.

Researchers say they have never seen such big and healthy animals. That may be because at the other end of the food chain, plankton are thriving in warmer waters.

Good shape

At the edge of the solid ice, the spring thaw is beginning and a whale count is under way. Research teams work round the clock monitoring the bowhead whales, which surface in open areas to breathe.

A research station in the Arctic

Once hunted almost to extinction, this population is now increasing by up to 3% a year. Retreating pack ice may also be helping them.

A team of researchers has also been monitoring the local polar bears from a helicopter.

They tranquillise, weigh and tag the animals. George Durner, from the Alaska Biological Science Center, says he has never seen the bears look in such good shape.

"The lengthening of the ice-free period may actually increase the amount of sunlight entering the ocean, triggering greater plant growth, plankton growth. This is the foundation of the food chain out there," he said.

Fish eat the plankton. Seals eat the fish, and polar bears feed on the seals.

Feeding opportunities

Scientists here are tracking the whales' movement under the ice with special microphones.

Further out where the sea ice is beginning to break up, another team is counting the whales as they come up to breathe.

Craig George, one of the team leaders, says the bowhead whale population is now increasing by three percent a year, after being hunted almost to extinction. He, too, says less ice may be helping them.

"Retreating the pack ice a little bit gives greater feeding opportunities in the Beaufort Sea where they summer," he said, adding: "Retreating ice out of the Canadian archipelago might allow them to enter areas where they haven't been for several thousand years."

Threatened way of life

Inupiat Eskimos are preparing for a whale hunt. They are allowed to catch a small number of whales for food, using traditional sealskin boats and harpoons.

A harpoon competition

Many hunters, like George Brower, have had to be rescued in recent years, after the ice on which they set up camp sheared away from the land unexpectedly.

"Our ice is changing out there. It's unstable. My livelihood is off the ocean. It's a lifestyle that I wouldn't trade for the world," he said.

He hopes to pass on his way of life to his sons and daughters, and hopes that they will carry on traditional ways. But he says, "It's getting more risky out there."

Limits to benefit

Some climate models predict that if warming continues at current rates, within 50 to 80 years there could be no Arctic ice at all during the summer.

That would allow more shipping through the region, bringing noise and pollution, which could hurt the bowhead population. Researcher George Durner says it would also be a disaster for the polar bears.

"If this ice-free period gets too long, then the period of time when polar bears can hunt for food becomes shorter and shorter because polar bears are so dependent on the ice platform for hunting for seals," he said.

It could reach a point where the ice period may be too short for polar bears to get enough food.

If the current warming trend does take hold, the comeback being made by animals in Alaska could soon be reversed.