Lewis Gordon Pugh loves to pioneer new swimming routes around or between landmarks once thought unswimmable. In 2006, he swam the drought-stricken Thames; also that year he became the first swimmer to do a long-distance swim in all five oceans of the world. The following year, he made the first long-distance swim across the North Pole -- where climate change made the ice temporarily disappear. Heading into the second decade of his swimming career, he's regarded as the greatest cold-water swimmer in history.

His swims have given him a sea-level view of our planet, and inspired him to do his bit to help preserve it. He left a career in maritime law to become a public speaker on environmental issues with his group, Polar Defence Project -- and of course to plan more astonishing swims and treks. In September 2008, Pugh and Robbie Hedgus kayaked across the Arctic Ocean into the polar ice pack, to raise awareness of the thinning sea ice and the dangers of climate change in the Arctic and across the world. And at the end of May 2010 he swam 1 kilometer across Pumori, a meltwater lake situated next to the Khumbu Glacier on Mount Everest, at an altitude of 5300 meters, to draw attention to the melting of the Asian glaciers. He completed the swim -- the highest any person has undertaken -- in less than 23 minutes. "Glaciers are not just ice: they are a lifeline, they provide water to 2 billion people, and we need to protect them," he says.