Melting Planet:

The polar bear is one of the natural world's most famous predators - the king of the Arctic wastelands. But, like its vast Arctic home, the polar bear is under unprecedented threat. Both are disappearing with alarming speed.

Thinning ice and longer summers are destroying the bears' habitat, and as the ice floes shrink, the desperate animals are driven by starvation into human settlements - to be shot. Stranded polar bears are drowning in large numbers as they try to swim hundreds of miles to find increasingly scarce ice floes. Local hunters find their corpses floating on seas once coated in a thick skin of ice.

It is a phenomenon that frightens the native people that live around the Arctic. Many fear their children will never know the polar bear. "The ice is moving further and further north," said Charlie Johnson, 64, an Alaskan Nupiak from Nome, in the state's far west. "In the Bering Sea the ice leaves earlier and earlier. On the north slope, the ice is retreating as far as 300 or 400 miles offshore."

Last year, hunters found half a dozen bears that had drowned about 200 miles north of Barrow, on Alaska's northern coast. "It seems they had tried to swim for shore ... A polar bear might be able to swim 100 miles but not 400."

His alarming testimony, given at a conference on global warming and native communities held in the Alaskan capital, Anchorage, last week, is just one story of the many changes happening across the globe. Climate change threatens the survival of thousands of species - a threat unparalleled since the last ice age, which ended some 10,000 years ago.

The vast majority, scientists will warn this week, are migratory animals - sperm whales, polar bears, gazelles, garden birds and turtles - whose survival depends on the intricate web of habitats, food supplies and weather conditions which, for some species, can stretch for 6,500 miles. Every link of that chain is slowly but perceptibly altering.

Europe's most senior ecologists and conservationists are meeting in Aviemore, in the Scottish Highlands, this week for a conference on the impact of climate change on migratory species, an event organised by the British government as part of its presidency of the European Union. It is a well-chosen location. Aviemore's major winter employer - skiing - is a victim of warmer winters. Ski slopes in the Cairngorms, which once had snow caps year round on the highest peaks, have recently been closed down when the winter snow failed. The snow bunting, ptarmigan and dotterel - some of Scotland's rarest birds - are also given little chance of survival as their harsh and marginal winter environments disappear.

A report being presented this week in Aviemore reveals this is a pattern being repeated around the world. In the sub-Arctic tundra,caribou are threatened by "multiple climate change impacts". Deeper snow at higher latitudes makes it harder for caribou herds to travel. Faster and more regular "freeze-thaw" cycles make it harder to dig out food under thick crusts of ice-covered snow. Wetter and warmer winters are cutting calving success, and increasing insect attacks and disease.

The same holds true for migratory wading birds such as the red knot and the northern seal. The endangered spoon-billed sandpiper, too, faces extinction, the report says. They are of "key concern". It says that species "cannot shift further north as their climates become warmer. They have nowhere left to go ... We can see, very clearly, that most migratory species are drifting towards the poles."

The report, passed to The Independent on Sunday, and commissioned by the Department for the Environment, Food and Rural Affairs (Defra), makes gloomy predictions about the world's animal populations. "The habitats of migratory species most vulnerable to climate change were found to be tundra, cloud forest, sea ice and low-lying coastal areas," it states. "Increased droughts and lowered water tables, particularly in key areas used as 'staging posts' on migration, were also identified as key threats stemming from climate change."

Some of itsfindings include:

The science magazine Nature predicted last year that up to 37 per cent of terrestrial species could become extinct by 2050. And the Defra report presents more problems than solutions. Tackling these crises will be far more complicated than just building more nature reserves - a problem that Jim Knight, the nature conservation minister, acknowledges.

A key issue in sub-Saharan Africa, for instance, is profound poverty. After visiting the Democratic Republic of the Congo last month, Mr Knight found it difficult to condemn local people eating gorillas, already endangered. "You can't blame an individual who doesn't know how they're going to feed their family every day from harvesting what's around them. That's a real challenge," he said.

And the clash between nature and human need - a critical issue across Africa - is likely to worsen. As its savannah and forests begin shifting south, migratory animals will shift along with them. Some of the continent's major national parks and reserves - such as the Masai-Mara or Serengeti - may also have to move their boundaries if their game species, the elephant and wildebeest, are to be properly protected. This will bring conflict with local communities.

There is also a gap in scientific knowledge between what has been discovered about the impact of climate change in the industrialised world and in less developed countries. Similarly, fisheries experts know more about species such as cod and haddock, than they do about fish humans don't eat.

Many environmentalists are pessimistic about the prospects of halting, let alone reversing, this trend. "Are we fighting a losing battle? Yes, we probably are," one naturalist told the IoS last month.

The UK, which is attempting to put climate change at the top of the global agenda during its presidency of the G8 group of industrialised nations, is still struggling to persuade the American, Japanese and Australian governments to admit that mankind's gas emissions are the biggest threat. These three continue to insist there is no proof that climate change is largely manmade.

And many British environmentalists suspect that Tony Blair's public commitment to a tougher global treaty to replace the Kyoto Protocol, aimed at a 60 per cent cut in carbon dioxide emissions by 2050, is not being backed up by the Government in private.

Despite President George Bush's resistance to a new global climate treaty, many US states are being far more radical. Even the G8 communiqué after the Gleneagles summit in July had Mr Bush confirming that the climate was warming.

In Alaska last week, satellite images released by two US universities and the space agency Nasa revealed that the amount of sea-ice cover over the polar ice cap has fallen for the past four years. "A long-term decline is under way," said Walt Meier of the National Snow and Ice Data Centre.

The Arctic's native communities don't need satellite images to tell them this. John Keogak, 47, an Inuvialuit from Canada's North-West Territories, hunts polar bears, seals, caribou and musk ox. "The polar bear is part of our culture," he said. "They use the ice as a hunting ground for the seals. If there is no ice there is no way the bears will be able to catch the seals." He said the number of bears was decreasing and feared his children might not be able to hunt them. He said: "There is an earlier break-up of ice, a later freeze-up. Now it's more rapid. Something is happening."

And now, said Mr Keogak, there was evidence that polar bears are facing an unusual competitor - the grizzly bear. As the sub-Arctic tundra and wastelands thaw, the grizzly is moving north, colonising areas where they were previously unable to survive. Life for Alaska's polar bears is rapidly becoming very precarious.

Vanishing from the earth

Mountain gorilla

Already listed as "critically endangered", only about 700 mountain gorillas, including the distinctively marked adult male silverbacks, migrate within the cloud forests of the volcanic Virunga mountains of the Democratic Republic of the Congo, Rwanda and Uganda. After a century of human persecution it faced extinction. Now its unique but marginal mountain forests - already heavily reduced by forestry - are shrinking, because of climate change. It will be forced to climb higher for cooler climates, but will effectively run out of mountain.

Across Africa, habitats are shifting as temperatures rise, or disappearing in droughts, affecting the migrations of millions of wildebeest, and savannah elephant and Thomson's gazelle. This will hit game reserves and national parks - forcing many to move their boundaries.

Green turtle

The number of male green turtles is falling because of rising temperatures, threatening their survival. Turtle nests need a temperature of precisely 28.8C to hatch even numbers of males and females. On Ascension Island, where nest temperatures are up 0.5C,females now outnumber males three to one. On Antigua too, nest temperatures for hawkbill turtles are higher than the ideal incubation level. Hatchling survival rates are also cut by higher temperatures. Egg-laying beaches for all species of turtle are being lost to rising sea levels. A third of nesting beaches in the Caribbean would be lost by a 50cm rise in sea level.

Saiga antelope

This rare antelope, thought to be half-way between an antelope and a sheep, and found in Russia and Mongolia, is "critically endangered". Hunted heavily, its autumn migration to escape bitter weather and spring migration to find water and food are being hit by unusual weather cycles. The antelope will be forced by climate instability to find new grazing areas, coming intoconflict with humans. Bad years can cut its numbers by 50 per cent, because of high mortality and poor birth rates.

Sperm whale

The migration of the sperm whale, one of the earth's largest mammals, made famous by Herman Melville's epic Moby-Dick, is closely linked to the squid, its main food source. Squid numbers are affected by warmer water and weather phenomena such as El Niño. Adult male sperm whales up to 20m long like cold water in the disappearing ice-packs. Warm water cuts sperm whale reproduction because food supplies fall. Around the Galapagos Islands, a fall in births is linked to higher sea surface temperatures. Plankton and krill, key foods for many cetaceans such as the pilot whale, have in some regions declined 100-fold in warmer water.