In 2007 Lewis Pugh attempted the impossible: to swim across the North Pole without any protection other than a pair of speedo swimming trunks.

This swim pushed the boundaries of what was thought to be humanly possible by subjecting a body to a long-distance swim in below-freezing (minus 1.7°C) water. But what made this swim even more significant was that it should not have been possible to swim across the North Pole at all; it should have been completely closed over by ice.

Lewis would go on to set records with pioneering swims at other extremes – furthest south in Antarctica, and the world's highest in the Himalayas. But this North Pole swim was a symbolic clarion call that showed the world how the effects of climate change were an acute and visible reality. Two years previously, 23% of the Arctic ice cover had melted. This swim made sure that the world knew about it.

Watch the video of this astonishing achievement below.