Editor's note: TED is a nonprofit organization devoted to "Ideas worth spreading," which it makes available through talks posted on its website. Swimmer Lewis Pugh spoke at the TED Global conference in July in Oxford, England.

(CNN) -- Lewis Pugh was standing in the Arctic in a Speedo about to plunge into water just shy of the freezing point when he came to grips with the challenge he was facing.

"My most dominant thought as I was standing on the edge of the sea ice," Pugh said, "was just how frightened I was. The water's completely black; there are chunks of white ice in the water."

Pugh said he remembered thinking that if things went wrong, "How long would it take for my frozen body to sink to the bottom of the ocean?" Pugh didn't sink, and he completed a one-kilometer swim in 29-degree Fahrenheit (or -1.7 degree centigrade) water. (Since it was salt water it was below the normal freezing point of water.) But it came at a price. He lost feeling in his hands for four months.

Watch an interview with Lewis Pugh

Pugh, a 40-year-old former reservist in Britain's special forces regiment, the Special Air Service, has gained worldwide attention for his extreme adventures, designed to dramatize the environmental threats to the planet. Whether it's swimming at the North Pole, or in a meltwater lake on Mount Everest, Pugh is constantly testing his own limits and calling attention to urgent issues.

"Swimming has been a very effective medium for telling a story about the state of our planet," Pugh told CNN.

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The son of an admiral in the British navy, Pugh and his family moved to South Africa when he was 10. Educated there and at Cambridge University, Pugh became a maritime lawyer but grew dissatisfied with the profession.

A friend said to him, "Lewis, if you don't follow your own dreams in life, then you're going to be following somebody's else's dreams."

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Swimming is his dream. His adventures have taken him to every ocean and many other bodies of water; swimming Norway's longest fjord, swimming the English Channel, swimming in the Maldives in the Indian Ocean, swimming the full length of the River Thames, swimming from Robben Island to Cape Town. "I want to swim until the last day of my life," Pugh says.

Pugh says he was driven to attempt record-setting coldwater swims because the warm-water swimming challenges had already been conquered.

He doesn't think that his ability to survive cold-water swimming adventures is due to any physical advantage over others, but rather to a resolve never to give up.

As he was about to dive into the Arctic, he says, that mental attitude came into play. "The most immediate thing you have to do is to just squeeze out the fear, because otherwise the fear will just paralyze you. And then commit 100 percent.... I wanted to swim a kilometer across the North Pole. And I wanted to do it to demonstrate graphically to the world what was happening in the Arctic, because the North Pole should be frozen over.

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"I remember thinking to myself, if things go bad, I'll get out after 500 meters...if you think about a swim like that, that's the worst way of thinking. What you're doing is confusing your subconscious, because you're planning for victory and defeat at the same time.

"So the only way I could get into that water was to get as aggressive as possible -- not wild aggression, controlled aggression -- and to get really focused, and then commit 100 percent to doing the full kilometer and then just dive in, go for it.

"It took me 18 minutes and 50 seconds, it was just grueling, make no bones about it. The human body is not designed for swimming in minus 1.7 degree centigrade water. The passengers of the Titanic perished in water of 5 degrees centigrade. So this water is 7 degrees centigrade colder. It's very grueling on the body, and afterward when I came out, my fingers were swollen.

"We're made partially of water, so the cells in my fingers had actually frozen and expanded and burst. It damaged the nerve cells, it took me four months to feel my fingers again, but now everything's fine.

"But the more lasting damage is the psychological impact it has on you because if you haven't felt your hands for four months, you are cautious about going and pushing the boundaries again."

Yet Pugh didn't let that stop him. In May, two and a half years after the Arctic swim, he was on Mount Everest, swimming in rarefied air at a high altitude. "One of the hardest things was to get back in water which was very, very cold, and at 5.5 kilometers above sea level."

Given the physical damage he suffered after the North Pole swim, Pugh says he "had to work hard on putting that swim behind me, forgetting about it, and starting with a fresh clean slate."

"It's almost like when a computer's got a virus, you clean that hard drive... that's what I had to do in my mind, clean my mind."

In the SAS, the special forces, he said, there is a saying that its initials stand for "speed, aggression, surprise." He adopted that approach in the world of coldwater swimming, swimming as fast as he could, with as much adrenalin as possible, to "fend off the cold." It didn't work in the high-altitude conditions of Mt. Everest.

"You can't bully Mt .Everest, it's very difficult to breathe up there...So I had to adopt a much calmer approach, one with a lot of humility, and I had to work with the mountain rather than against the mountain." Pugh swam more slowly, using the breaststroke, and completed the kilometer in just under 23 minutes. [In more normal water conditions, he swims a kilometer in about 14 minutes.]

Pugh says his father and mother, who was a nursing officer in the British navy, set an example of persistence. "Those people from that generation were not quitters."

"I just never, ever want to give up. Most battles are won in the 11th hour, and most people give up," he says. "If you give up once, it's quite hard. If you give up a second time, it's a little bit easier. Give up a third time, it's starting to become a habit."

Pugh is planning for another epic challenge, but he won't say what it will be. The only hint he will give is that it will dramatize a threat to another of the world's major ecosystems.

"The problem with climate change is that it's quite complicated for the ordinary person to understand." Scientists will constantly refine their work, giving new and varied interpretations of the data, and people may get confused. He's hoping his swims can help:

"They're not confused when they see somebody swimming across the North Pole, across an open patch of sea."