If anything symbolises the Arctic it is surely nanuk, the great white bear. He is a wanderer and a hunter, and a fair match for man in the white infinity of his polar world. Every inch of the Arctic lies within his grasp: nanuk has been sighted more than a mile up on the Greenland ice cap, he’s been found denning at the bottom of Hudson Bay, just 53 degrees north, and purposefully striding the ice within 100 miles of the pole itself.

“I used to think that the land would stop them,” says Ray Schweinsburg, a Canadian polar bear biologist, “but I think they can cross any terrain. The only thing that stops them is a place where there is no food.”

And for polar bears, having sufficient food to live means lots of sea ice.

Polar bears, it’s true, will deign to catch lemmings, or scavenge dead birds if the opportunity presents itself, but it’s sea ice and netsik — the ringed seal that lives and breeds there — that are at the core of the creature’s economy.

The plight of the harp seals living in the Gulf of St Lawrence gives us a clear idea of the shape of things to come. Like the ringed seals, they can raise no pups when there is little or no sea ice present — which happened to them in 1967, 1981, 2000, 2001 and 2002. The run of pupless years that opened this century is worrying.

When a run of ice-free years exceeds the reproductive life of a female ringed seal — perhaps a dozen years at most — the Gulf of St Lawrence population, which is genetically separate from the rest of the species, will become extinct. Ringed, ribbon and bearded seals also give birth and nurse on the sea ice. Even the mighty walrus lives under the spell of a frozen sea, for the highly productive ice-edge is its prime habitat.

The great bears are slowly starving as each winter becomes warmer than the one before. A long-term study of 1,200 individuals living in the south of their range — around Hudson Bay — reveals that they are already 15 per cent skinnier on average than they were a few decades ago. The feeding season has become just too short for the bears to find enough food, and 15 per cent is a lot of body fat to lose before hibernation.

With each year, starving females give birth to fewer cubs. Some decades ago triplets were common; they are now unheard of. And back then around half the cubs were weaned and feeding themselves at 18 months, while today that number is less than 1 in 20. Even those females that successfully give birth face dangers unknown of in times past — increasing winter rain in some areas may collapse birthing dens, killing both the mother and cubs sleeping within.

And the early break-up of the ice can separate denning and feeding areas; young cubs cannot swim the distances required to find food. When this happens they will simply starve to death.

As Schweinsburg says, the only thing that stops a nanuk is a place where there is no food. And in creating an Arctic with dwindling sea ice, we are creating a monotony of open water and dry land where, for the bears at least, there is no food.

If nothing is done to limit greenhouse gas emissions, it seems certain that sometime this century a day will dawn when no summer ice will be seen in the Arctic — just a vast, dark, turbulent sea.

My guess is that the world will not have to wait even that long to be done with the nanuk.

The changes we’re witnessing at the Poles are of the runaway type, meaning that unless greenhouse gases can be limited — and quickly — there can be no winners among the fauna and flora unique to the region. Instead we should expect that the realm of the polar bear, the narwhal and the walrus will simply be replaced by the largest habitat on Earth — the great temperate forests of the Taiga, and the cold, ice-free oceans of the north.

Any polar bears or seals surviving in zoos, which have been kept in the hope of one day re-creating their icy realm, will remain captive; after persisting for millions of years the north polar cryosphere will have vanished for ever.

© Tim Flannery 2006. Extracted from The Weather Makers, to be published by Allen Lane on March 2, £20 (www.penguin.co.uk) Available for £18 from Times Books First, 0870 1608080, www.timesonline.co.uk/booksfirstbuy

How Climate Change Shapes Our World

A discussion at St Paul’s Cathedral between Tim Flannery, David Attenborough and Claire Foster, policy adviser to the Church of England.

March 6, 2006, 6.30-8pm. Admission free. Visit www.timesonline.co.uk/weathermakers for tickets.

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