The Arctic ice cap has collapsed at an unprecedented rate this summer and levels of sea ice in the region now stand at a record low, scientists said last night. Experts said they were "stunned" by the loss of ice, with an area almost twice as big as Britain disappearing in the last week alone. So much ice has melted this summer that the north-west passage across the top of Canada is fully navigable, and observers say the north-east passage along Russia's Arctic coast could open later this month. If the increased rate of melting continues, the summertime Arctic could be totally free of ice by 2030.

Mark Serreze, an Arctic specialist at the US National Snow and Ice Data Centre at Colorado University in Denver which released the figures, said: "It's amazing. It's simply fallen off a cliff and we're still losing ice." The Arctic has now lost about a third of its ice since satellite measurements began 30 years ago, and the rate of loss has accelerated sharply since 2002.

Dr Serreze said: "If you asked me a couple of years ago when the Arctic could lose all of its ice, then I would have said 2100, or 2070 maybe. But now I think that 2030 is a reasonable estimate. It seems that the Arctic is going to be a very different place within our lifetimes, and certainly within our children's lifetimes."

The new figures show that sea ice extent is currently down to 4.4m square kilometres (1.7m square miles) and still falling. The previous record low was 5.3m square kilometres in September 2005. From 1979 to 2000 the average sea ice extent was 7.7m square kilometres. The minimum extent of sea ice usually occurs late in September each year, as the freezing Arctic winter begins to bite.

The sea ice usually then begins to freeze again over the winter. But Dr Serreze said that would be difficult this year. "This summer we've got all this open water and added heat going into the ocean. That is going to make it much harder for the ice to grow back. What we've seen this year sets us up for an even worse year next year." The winter ice has already failed to make up for increased losses in the summer in each of the last two years.

Changes in wind and ocean circulation patterns can help reduce sea ice extent, but Dr Serreze said the main culprit was man-made global warming. "The rules are starting to change and what's changing the rules is the input of greenhouse gases. This year puts the exclamation mark on a series of record lows that tell us something is happening."

The dramatic loss is further bad news for the region's wildlife which relies on the sea ice, such as polar bears. The animals use its coastal fringes to find food, and as the summer ice retreats to the north, they must swim further to hunt for seals. Some colonies of bears have already showed signs of malnutrition and biologists say there could be a severe drop in their population within a few decades, though they may not go extinct.

Yesterday's announcement will also increase political interest in the Arctic, with a number of countries currently jostling to exploit the oil and gas reserves believed to lie under the ocean, which could become more accessible as the icy cover retreats. Last month Russia claimed a huge area around the north pole, and Denmark and Canada are preparing similar claims, which rely on showing that a chain of underwater mountains that runs across the region are connected to their respective continental shelves.

Guardian