Melting of Arctic ice 'fascinating ... alarming'
For scientists, this year's ice season was like the NHL playoffs.
They placed bets, pored over satellite images, and speculated endlessly on how much Arctic ice would survive the summer.
"Everyone was following it," said Louis Fortier, scientific director of the Arcticnet, which funds and co-ordinates much of Canada's polar research. "It was like the hockey final."
At one point, it looked like 2008 might shatter last year's retreat of ice.
So much ice had melted by the end of August it was possible for the first time in human history to circumnavigate the North Pole, prompting one prominent U.S. scientist to say the ice cap has entered a "death spiral."
In the end, the ice cap survived for at least another year. The U.S. National Ice and Snow Data Center is expected to issue its wrap-up report Thursday, which will confirm 2008's Arctic retreat as the second worst on record after 2007's stunning loss.
But the ice that survived is in precarious shape heading into the winter.
Most of it is first-year ice less than a metre thick, says Walt Meier, a research scientist at the U.S.-based centre, which tracks the ice by satellite as it waxes and wanes through the year.
Thick, multi-year ice used to cover much of the Arctic Ocean year-round. All that is left of that cement-like ice is now jammed up in a strip against Canada's Arctic islands and northern Greenland.
The rest of the old, hard ice either melted this summer or was flushed down into the Atlantic Ocean, where it disintegrated.
"We're left with much less multi-year ice compared to the same time last year," said Meier.
"So even though there is more ice total, most of it is the first-year variety that is pretty thin."
In many ways, 2008 was "as remarkable or even more remarkable" than 2007, he says, because the ice did not bounce back despite summer conditions that were much cooler than the 2007 Arctic heat wave.
Now that the 2008 numbers are in, researchers are revising their estimates on how much longer the Arctic summer ice can survive.
Fortier says it is a bit of game and "exciting" for scientists to see their predictions about climate change coming true much faster than expected.
However, "what is so fascinating from a scientific point of view is also very alarming," he said.
The rapid pace of change in the North suggests the scientific community and the United Nations Intergovernmental Panel on Climate Change have likely also underestimated the pace of other climate changes coming down the pipe.
"The Arctic is a bellwether for change that is coming globally and is coming much faster than any of the models suggested it should," said David Barber, an ice specialist at the University of Manitoba.
Or, as Fortier at Laval University puts it: "I think we are in for a few surprises."
The iconic ice cap has topped the planet for eons. But in the last two years the sea ice retreated by summer's end by more than half, to well below five million square kilometres.
Both years it retreated to more than 30 per cent below the average minimum seen between 1979 to 2000.
Many polar watchers believe the ice has passed a "tipping point" and will soon give way to open water in late summer.
Barber says sediments from the sea floor indicate the Arctic has had ice continuously for 1.1 million years.
Fortier says it may be even longer, pointing to studies that indicate multi-year ice pack has been carrying driftwood from Siberia across to Greenland for close to 14 million years.
Meier says there is a possibility the ice melted back during warm spells 8,000 and 130,000 years ago.
But he stresses this is the first time humans have played the lead role in driving the retreat.
There is widespread scientific consensus that rising atmospheric temperatures caused by greenhouse gas emissions are largely responsible for the big melt.
As the ice retreats more solar energy is being absorbed by the dark Arctic waters, raising the temperature of the ocean surface, which then slows formation of new ice as the winter chill sets in.
There is also evidence more water is flowing into the Arctic from the Pacific and Atlantic, carrying heat with it.
"It's like the ice is between two fires -- the atmospheric heat and the ocean heat," says Fortier.