The staggering decline of sea ice at the frontline of climate change

We are a few hundred miles from the north pole. The air temperature is -3C, the sea freezing. All around us in these foggy Arctic waters at the top of the world are floes – large and small chunks of sea ice that melt and freeze again with the seasons.

Arne Sorensen, our Danish ice pilot, is 60 feet up in the crow's nest of the Arctic Sunrise vessel. Visibility is just 200 yards and he inches the 1,000-tonne Greenpeace ice breaker forward at two knots through narrow passages of clear water. The floes are piled up and compressed in fantastic shapes and shades of grey and blue; they crack, rumble and groan as we nudge them aside or climb over them. Two polar bears on our port side lift their heads but resume hunting.

Sorensen has sailed deep into ice at both poles for 30 years, but this voyage is different, he says. The edge of the Arctic ice cap is usually far south of where we are now at the very end of the melt season. More than 600,000 square kilometres (sq km) more ice has melted in 2012 than was ever recorded by satellites before. Now the minimum extent has been nearly reached and the sea is starting to refreeze.

"This is the new minimum extent of the ice cap," he says, the "frontline of climate change".

"It is sad. I am not doubting this is related to emitting fossil fuels to a large extent. It's sad to observe that we are capable of changing the planet to such a degree."

The vast polar ice cap, which regulates the Earth's temperature and has been a permanent fixture in our understanding of how the world works, has this year retreated further and faster than anyone expected. The previous record, set in 2007, was officially broken on 27 August when satellite images averaged over five days showed the ice then extended 4.11 million sq km, a reduction of nearly 50% compared to just 40 years ago.

But since 27 August, the ice just kept melting – at nearly 40,000 sq km a day until a few days ago. Satellite pictures this weekend showed the cap covering only 3.49m sq km. This year, 11.7m sq km of ice melted, 22% more than the long-term average of 9.18m sq km. The record minimum extent is now likely to be formally called on Monday by the US National Snow and Ice Data Centre (NSIDC) in Colorado.

The record hasn't just been broken, it's been smashed to smithereens, adding weight to predictions that the Arctic may be ice-free in summer months within 20 years, say British, Italian and American-based scientists on board the Arctic Sunrise. They are shocked at the speed and extent of the ice loss. More