Ten years after his pioneering swim across the North Pole, Lewis Pugh returned to the Arctic to see for himself how the area had weathered a decade of global warming. What he found was alarming.

To prepare for his kilometre-long swim across the edge of the Arctic sea ice, Lewis revisited his former training grounds off Svalbard. The sea temperature there sounded the first warning: a decade earlier it had been a brisk 3°C, now it was 10°C – not nearly cold enough to condition him properly for the swim to come.

Travelling further north, the team was shocked to see the rapid retreat of familiar glaciers. Perhaps our greatest shock came during the swim itself: although Lewis is arguably the world's most seasoned cold-water swimmer, he came close to losing his life on the edge of the sea ice in what turned into a 22-minute swim – his longest ever.

Sky News was there to document the swim – watch their documentary Arctic Peril for the full story.