Ice is melting so fast in the Arctic that the North Pole will be in the open sea in 30 years, according to a team of leading climatologists.

Ships will be able to sail over the top of the world and tourists will be able visit what was, until climate change, one of planet’s most inaccessible landscapes.

Researchers assessing the impact of carbon emissions on the world’s climate have calculated that late summer in the Arctic will be ice-free by 2040 or earlier - well within a lifetime.

Some ice would still be found on coastlines, notably Greenland and Ellesmere Island, but the rest of the Arctic Ocean, including the pole, would be open water.

The Nasa-funded US team of researchers said the ice retreat is likely to remain fairly constant until 2024 when there will be a sudden speeding up of the process.

In between 30 and 50 years, they concluded, summer sea ice will have vanished from almost the entire Arctic region.

Their finding may, however, already be out of date and something of an over-optimistic forecast, said Professor Chris Rapley, head of the British Antarctic Survey.

He said a recent study by the Global Carbon Project suggests emissions are rising more than twice as fast as in 2000 which is likely to speed up ice-loss even further.

"The study findings may be an under estimate of when the Arctic summer ice might be all gone," he said. "It could well be their assumptions are more optimistic than they might be."

He described the report as "worrying" but said it fitted into recent findings based on satellite observations of the speed at which ice is retreating.

Arctic ice is being hit by the double effects of loss of reflectivity and warmer currents being washed into the ocean.

Scientists have long realised that ice reflects heat and as the quantity reduces so, too, does the amount of heat that can be bounced away from the Earth.

However, the study team from the National Centre for Atmospheric Research in Colorado, US, and two US universities, identified warmer ocean currents as an additional factor to be considered.

Disappearing ice is already causing problems for the Polar Bear and it is likely to be driven to the brink of extinction unless it can find ways of adapting.

Other wildlife, including seals, are also likely to suffer, though not so badly but the removal of sea ice is likely to benefit a range of marine creatures, including cod, which could move in to the open waters.

For people the open waters are likely to lead to fresh opportunities, though the Inuit lifestyle would be damaged.

Tourist could open up to allow visitors Arctic cruises with cocktail parties over the North Pole that previously defied the best efforts of many explorers.

Oil companies would move in to tap resources previously protected by the ice and freight firms could use the ocean as a shortcut.

Winter ice will still remain because temperatures will plunge during the winter when there is no sun to heat up the region but it will melt faster each year because less will form.

The US study team modified one of the climate models used by the United Nation’s Intergovernmental Panel on Climate Change to establish what will happen to the ice as carbon emissions rise.

"We have already witnessed major losses in sea ice, but our research suggests that the decrease over the next few decades could be far more dramatic than anything that has happened so far," said Professor Marika Holland who led the study. "These changes are surprisingly rapid."

"As the ice retreats, the ocean transports more heat to the Arctic and the open water absorbs more sunlight, further accelerating the rate of warming and leading to the loss of more ice. This is a positive feedback loop with dramatic implications for the entire Arctic region."

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