If whiteness no longer means an evolutionary edge, polar bears will find it harder to sneak up on prey in Alaska, for instance, while white hares in Russia may be snatched more often by eagles and other predators.

Many species are under pressure in the Arctic, where scientists say global warming is happening faster than anywhere else on the planet. At the other end of the world, the thick Antarctic ice cap acts as a deep freeze that brakes any warming.

In what may be a portent of bigger problems, three polar bears - usually top of the Arctic food chain - were reduced to scavenging on sea birds' eggs this year after receding sea ice left them stranded on a remote North Atlantic island.

The mother and two cubs have since disappeared from Norway's Bear Island, probably in a vain bid to swim north about 125 miles to reach colder islands or the receding sea ice where seals are more plentiful.

"Animals that have adapted by turning white during the winter as camouflage may not have enough time to adapt to a world in which winters are no longer white," said Samantha Smith, director of the WWF environmental group's Arctic Program.

WHITE AS SNOW? NOWHERE TO GO

"And they are likely to have no place to go northwards as temperatures rise in their current habitat," she said.

Ptarmigan, a grouse-like bird whose plumage changes in winter to white from brown, may die out in places like Scotland if snows fail. They cannot know that they might survive, for instance, by flying north over the sea to Iceland.

Types of Arctic foxes, hares, arctic tern, weasels, ermine and lemmings are among the animals that change color in winter to help them hide. Always white, polar bears evolved from brown bears perhaps 200,000 years ago.

The stranded polar bears' problems started when the mother apparently came out of her winter den late, after the sea ice had already melted from around the island with the spring thaw. The cubs were too small to swim. "We think they eventually tried to swim north to reach the ice," said Sissel Aarvik, an environmental official on the Arctic archipelago of Svalbard north of Bear Island.

"The mother might have made it but it's probably too far for a cub," she said.

Scientists say that emissions of carbon dioxide from burning fossil fuels, in everything from cars to power plants, are blanketing the globe and driving up temperatures.

Scientists say that carbon dioxide traps heat from the sun like the glass windows of a greenhouse. Carbon dioxide levels in the atmosphere have jumped by 30 percent since the Industrial Revolution in the 18th century."

Around the Arctic, the environment faces huge changes. Melting is happening fastest in the North partly because dark ground or sea water, when exposed, soaks up more heat than reflective snow or ice.

Warming is spreading new types of vegetation northwards where more southerly species of insects, birds and mammals are getting a foothold. People living in the North are struggling to adapt.

SEALS, WHALES

"Indigenous people who've relied on polar bears, seals, walrus and bowhead whales are being confronted by a whole new ecology," said Bob Corell, U.S. chairman of an eight-nation report into Arctic climate change to be published in November.

Canada's icy Hudson Bay could be uninhabitable for polar bears within just 20 years because of receding ice, he said.

He said it was unclear how far whiteness may become a liability. "These are some of the additional factors we're going to have to look at," he said.

Populations of Arctic foxes, many of which change in winter to white from brown, have shrunk even though many countries have long had them on protected lists.

"From Alaska to Scandinavia, Arctic fox populations are going down," said Nina Eide at the Norwegian Institute for Nature Research. "At the same time, the red fox is gaining ground."

She said it was hard to pin down how much of the Arctic fox decline was due to climate change. Other factors such as more human settlements make more food available - a turned-over rubbish bin can contain a feast for a fox.