British explorer Pen Hadow, centre, poses with team members Ann Daniels, right, and Martin Hartley, left, in their polar immersion suits in a lake in London's Hyde Park in October 2007. (Lefteris Pitarakis/AP Photo)

Three British explorers have launched an international scientific expedition to the North Pole to measure how quickly the Arctic Ocean's sea-ice cover may be melting.

The explorers — Pen Hadow, Ann Daniels and Martin Hartley — left Resolute Bay in Canada's Arctic by plane on Saturday on the way to the North Pole ice cap. There, they will spend about 100 days and travel by foot in temperatures that could reach as low as –50 C to measure the ice cap's thickness.

The ice cap is in danger and melting at an accelerating rate, the explorers said. The survey will capture data about the thickness of the ice and help to determine the lifespan of the ice cap, they said.

"This is a huge challenge we've set ourselves: to do the journey and the survey ourselves in the world's most extreme environment," said Hadow, adding the expedition took five years to plan.

A plane will resupply team members, and if it cannot land where they're stationed, the supplies will be dropped by air, according to the team's website.

The data the team gathers will be sent back to scientists in the United States for analysis, the scientists said.

With files from the Associated Press