Endurance swimmer Lewis Gordon Pugh is planning a swim more than 17,000ft (5,300m) up Mount Everest to highlight the impact of global warming.
Devon-born Mr Pugh, nicknamed the "polar bear" after swimming across the polar ice-cap, will be swimming 1km (0.62 miles) across a glacial lake.
Lawyer Mr Pugh, 39, has been training on Dartmoor, where he grew up, for the challenge in April 2010.
He hopes to draw attention to fears about the melting of glaciers.
Mr Pugh will swim in just his trunks, swimming cap and goggles and expects to spend about 20 minutes in the waters of the Khumbu Glacier.
Two years ago Mr Pugh swam for almost 20 minutes across a patch of open sea at the North Pole to raise awareness of the effects of rising temperatures on the Arctic.
He told BBC News: "Very few people had heard about it and I hope that in some small way that put pressure on the world leaders.
"The Himalayas are the next battleground."
He is hoping to draw attention to the problem ahead of a conference in Copenhagen in December on replacing the 1997 Kyoto protocol on reducing greenhouse gases.
Mr Pugh said the melting of the glaciers in the Himalayas region raised the risk of flooding and future water shortages.
He said: "We stand at a very important moment in the history of the world.
"I spend a lot of time in the Arctic and every year I see less and less sea ice and glaciers retreating."
Mr Pugh said the rivers of Dartmoor where he grew up were a "very good place" for training.
"The main thing is to prepare yourself in your mind," he said.
"If your mind can see something from beginning to end then your body will follow."
He added: "Obviously you have to do the swim and that can be excruciatingly painful."