Ships will be able to sail in open water to the North Pole in the summer of 2020, according to a study that found a rapid acceleration in the loss of sea ice.

The Arctic will be ice-free in summer within 20 years, the study found, while the Earth will lose the white cap that can be seen in photographs taken from space.

The Polar Ocean Physics Group from Cambridge University compared measurements of ice thickness recorded by a Royal Navy nuclear submarine with those taken two years later in the same area by Pen Hadow, the explorer.

The two sets of measurements were consistent, revealing that the findings by HMS Tireless in 2007 were not an aberration caused by a particularly warm year.

Peter Wadhams, Professor of Ocean Physics at Cambridge, said that cargo ships would no longer need to rely on special ice-breaking vessels to cross from the Pacific to the Atlantic via the Northwest Passage. The route would be ice-free for several months every year, cutting more than 3,000 miles from the normal journey from the Far East to Europe via the Suez canal.

“The North Pole will be exposed in ten years. You would be able to sail a Japanese car carrier across the North Pole and out into the Atlantic,” Professor Wadhams said.

“The ice will retreat to a zone north of Greenland and Ellesmere Island by 2020 and that area will be less than half the present summer area. The change in the Arctic summer sea ice is the biggest impact global warming is having on the physical appearance of the planet.”

This month, the National Snow and Ice Data Centre, which is part of the University of Colorado, said that Arctic ice coverage was the third-lowest since satellite records began in 1979.

The coverage was greater than in 2007 and 2008 largely because of cloudy skies during late summer. Each of the past five years has been one of the five lowest years.

Professor Wadhams, who was on board the submarine supervising sonar measurements of the ice, said that Mr Hadow’s findings confirmed that the underlying trend was towards increasingly thin and patchy ice cover.

Mr Hadow and his two team members spent 73 days between March 1 and May 7 this year walking 280 miles (450.6km) across the Arctic while taking measurements.

They drilled 1,500 holes and found that the average thickness of ice floes was 1.8m (5.9ft).

This was too thin to have survived the previous year’s summer melting and indicated that the area of moving ice had been formed in open sea during the winter.

Mr Hadow said that future expeditions to the Arctic in summer would need to change their techniques and equipment to cope with more frequent stretches of open water.

“A hundred years ago explorers used dogs to haul sledges and then we went through the stage of people hauling sledges,” he said. “Now we have people wearing immersion suits and needing to swim, with the sledge floating. I foresee a time when the sledge will become more of a canoe.”

Mr Hadow said that he had decided to change the focus of his polar expeditions from exploration to collecting data that could help to predict changes in the climate.

Martin Summerkorn, climate change adviser to the WWF Arctic Programme, said that the loss of sea ice predicted by the Cambridge study would have profound consequences beyond the polar region.

Without ice to reflect sunlight, the Arctic Ocean would warm more quickly, resulting in the release of greenhouse gases stored in the Arctic permafrost soils. These soils contain twice as much carbon as is in the atmosphere.

Mr Summerkorn said that the warming of the Arctic surface waters would accelerate the melting of the Greenland ice sheet, speeding up the sea level rise. “This could lead to flooding affecting one quarter of the world’s population and extreme global weather changes,” he said.

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