LONDON (Reuters) - A British adventurer is planning to highlight the effects of global warming by becoming the first person to swim at the North Pole and break his own record for the coldest swim.

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Sporting just a cap, trunks and goggles, Lewis Gordon Pugh will swim 1 km (0.6 miles) in water at a temperature of minus 1.8 degrees Celsius on July 15, a dip he expects to last 21 minutes.

Such a swim would have been impossible as little as 10 years ago because the water would have been frozen, Pugh says.

“Most people have no idea that you can find patches of open sea at the North Pole in summer,” said Pugh, who set the record for the coldest human swim off Antarctica at 0 degrees Celsius.

“I can’t think of a better way to show that climate change is a reality than by swimming in a place that should be totally frozen over. I hope it will ... put pressure on the leaders of the G8 summit to cut carbon emissions dramatically,” he said in a statement.

Climate change is expected to be high on the agenda at a meeting of the Group of Eight leading industrial countries in Germany next month.

Last year Pugh broke his own world record for the longest ice water swim by covering 1.2 km in a fjord in the Norwegian mountains, staying in the water for 23 minutes 50 seconds.

Any normal person would hyperventilate, suffer extreme shock and drown within minutes of jumping into near freezing water, but Pugh -- nicknamed the Polar Bear because of his ability to withstand freezing temperatures -- is made of sterner stuff.

In preparation for his swim, Pugh, 37, has increased his body weight from 87 kg to 105 kg by eating six meals a day, and has trained by swimming in a specially designed ice pool.

“This is the coldest water any human being will have swum in and Lewis has been extraordinarily dedicated,” Professor Tim Noakes of the University of Cape Town, an expert on the effect of cold water on the human body, said in the statement.

Pugh will spend his last month of training at a Norwegian glacial lake with Jorgen Amundsen, a relative of Roald Amundsen, the first man to reach the South Pole in 1911.

“This expedition represents the end of an era of Arctic exploration as we know it,” said Amundsen, who will ski the last 10 km to the North Pole with Pugh before his swim.

“It’s becoming increasingly difficult to walk to the North Pole and many expeditions fail each year when they encounter big stretches of open sea,” added Amundsen.

Pugh, a lawyer and “ambassador” for the environmental group WWF, says he is the only person to have completed a long distance swim in each of the five oceans, and last year he swam the length of England’s 203-mile River Thames.