Parts of the Arctic have experienced an unprecedented heatwave this summer, with one research station in the Canadian High Arctic recording temperatures above 20C, about 15C higher than the long-term average.
The high temperatures were accompanied by a dramatic melting of Arctic sea ice in September to the lowest levels ever recorded, a further indication of how sensitive this region of the world is to global warming. Scientists from Queen's University in Ontario watched with amazement as their thermometers touched 22C during their July field expedition at the High Arctic camp on Melville Island, usually one of the coldest places in North America.
"This was exceptional for a place where the normal average temperatures are about 5C. This year we frequently recorded daytime temperatures of between 10C and 15C and on some days it went as high as 22C," said Scott Lamoureux, a professor of geography at Queen's.
"Even temperatures of 15C are higher than we'd expect and yet we recorded them for between 10 and 12 days during July. We won't know the August and September recordings until next year when we go back there but it appears the region has continued to be warm through the summer."
The high temperatures on the island caused catastrophic mudslides as the permafrost on hillsides melted, Professor Lamoureux said. "The landscape was being torn to pieces, literally before our eyes."
Other parts of the Arctic also experienced higher-than-normal temperatures, which indicate that the wider polar region may have experienced its hottest summer on record, according to Walt Meir of the US National Snow and Ice Data Centre in Colorado.
"It's been warm, with temperatures about 3C or 4C above normal for June, July and August, particularly to the north of Siberia where the temperatures have reached between 4C and 5C above average," Dr Meir said.
Unusually clear skies over the Arctic this summer have caused temperatures to rise. More sunlight has exacerbated the loss of sea ice, which fell to a record low of 4.28 million square kilometres (1.65 million square miles), some 39 per cent below the long-term average for the period 1979 to 2000. Dr Meir said: "While the decline of the ice started out fairly slowly in spring and early summer, it accelerated rapidly in July. By mid-August, we had already shattered all previous records for ice extent."
An international team of scientists on board the Polar Stern, a research ship operated by the Alfred Wegener Institute in Germany, also felt the effects of an exceptionally warm Arctic summer. The scientists had anticipated that large areas of the Arctic would be covered by ice with a thickness of about two metres, but found that it had thinned to just one metre.
Instead of breaking through thicker ice at an expected speed of between 1 and 2 knots, the Polar Stern managed to cruise at 6 knots through thin ice and sometimes open water.
"We are in the midst of a phase of dramatic change in the Arctic," said Ursula Schauer, the chief scientist at the Alfred Wegener Institute, who was on board the Polar Stern expedition. "The ice cover of the North Polar Sea is dwindling, the ocean and the atmosphere are becoming steadily warmer, the ocean currents are changing," she said.
One scientist came back from the North Pole and reported that it was raining there, said David Carlson, the director of International Polar Year, the effort to highlight the climate issues of the Arctic and Antarctic. "It makes you wonder whether anyone has ever reported rain at the North Pole before."
Another team of scientists monitoring the movements of Ayles Ice Island off northern Canada reported that it had broken in two far earlier than expected, a further indication of warmer temperatures. And this summer, for the first time, an American sailing boat managed to traverse the North-west Passage from Nova Scotia to Alaska, a voyage usually made by icebreakers. Never before has a sail-powered vessel managed to get straight through the usually ice-blocked sea passage.
Inhabitants of the region are also noticing a significant change as a result of warmer summers, according to Shari Gearheard, a research scientist at the National Snow and Ice Data Centre. "People who live in the region are noticing changes in sea ice. The earlier break-up and later freeze-up affect when and where people can go hunting, as well as safety for travel," she said.
Mark Serreze of the National Snow and Ice Data Centre, said: "We may see an ice-free Arctic Ocean in summer within our lifetimes. The implications... are disturbing."
The North-west Passage: an ominous sign
The idea of a North-west Passage was born in 1493, when Pope Alexander VI divided the discovered world between Spain and Portugal, blocking England, France and Holland from a sea route to Asia. As it became clear a passage across Europe was impossible, the ambitious plan was hatched to seek out a route through north-western waters, and nations sent out explorers. When, in the 18th century, James Cook reported that Antarctic icebergs produced fresh water, the view that northern waters were not impossibly frozen was encouraged. In 1776 Cook himself was dispatched by the Admiralty with an Act promising a £20,000 prize, but he failed to push through a route north of Canada. His attempt preceded several British expeditions including a famous Victorian one by Sir John Franklin in 1845. Finally, in 1906 Roald Amundsen led the first trip across the passage to Alaska, and since then a number of fortified ships have followed. On 21 August this year, the North-west Passage was opened to ships not armed with icebreakers for the first time since records began.