Three British explorers on a mission to measure the thickness of the remaining polar ice have now departed on their 1,000km trek to the North Pole.

Pen Hadow, Ann Daniels and Martin Hartley were successfully dropped on to the permanent floating sea ice 668 miles off the Canadian mainland after a seven hour flight from their base in Resolute Bay on Saturday.

The trio will now spend the next 90 days taking more than 10million measurements with a specially developed ice-penetrating radar.

The Catlin Arctic Survey, sponsored by Green Guardian, is the first of its kind and the information gathered from the pole will arm scientists with valuable data about how fast the Arctic Ocean’s ice is melting.

Project director Pen Hadow, 47, stressed the mission was fundamentally different from adventure expeditions.

He said: “We’re only doing this because there is such an urgent need for more ground-truthing data about the permanent floating sea ice.

“If, as scientists tell us, the ice is thinning quickly, then it should set alarm bells ringing around the world.

“Personally I’d say the loss of such a magnificent, but precarious, feature on the surface of the planet would be a tragedy.”

The explorers are currently battling temperatures of -36c and, as well as the threat of attack from polar bears, the team will have to navigate their way across thin ice with sledges weighing 120kg and swim in freezing arctic waters when skiing becomes impossible.