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Trips over ice to the North Pole may be impossible in summer in just a decade or two because of global warming, says one of the world's leading polar adventurers.

Norwegian Boerge Ousland, who has skied alone across the Arctic Ocean and the Antarctic, said he would recommend one piece of equipment for anyone planning a trek to the North Pole in a few years: a kayak.

"It's a bit strange to think that the trips I have been doing may not be possible in 10-20 years," he told reporters after attending a climate seminar in the Norwegian Parliament. "But it may well happen."


That would end just over a century of trips across the ice - American Robert Peary was the first to claim to reach the North Pole, in 1909.

"Over time I have seen the changes myself," said Ousland, aged 45, who has been to the North Pole several times.

On a first trip in 1990 the ice was about three metres thick around the North Pole. Now it is 30 per cent thinner," he said.

There were also far more, wider gaps in the ice with open water, requiring risky swims in a special survival suit while tugging provisions and other gear along in a floating sledge.

The Arctic ice shrank in September this year to the smallest on record, eclipsing a 2005 low, according to US satellite data.

It is now expanding again as winter approaches but many climate scientists say that the ice could vanish in summer well before the end of the century because of a build-up of greenhouse gases, mainly from burning fossil fuels.

And the summer ice now starts several hundred kilometres further north than a century ago.

Few expeditions can now begin from Russia's Cape Arkticheskiy, as Ousland did in 1990, because a helicopter ride is needed to reach firm ice.

The receding ice is also revealing new islands.

This year, Ousland and a colleague, retracing an 1896 trip by Norwegian polar hero Fridtjof Nansen, found that an island called Northbrook Island in the Russian Arctic was in fact two - melting ice had exposed a channel between them.

They took a photograph of walruses swimming between the two islands.

Polar bears in the region looked thin, forced to eat nesting seabirds rather than seals, which live on the ice.

Ousland said that even a trip he made with South African Mike Horn starting in January 2006 - the first winter trek to the North Pole - revealed gaps in the ice.

"It was a shock to find open ice," he said. "We swam five to six times on that expedition because the ice was so thin."