THE Arctic could be ice-free in summer within five years, scientists have warned.
Sea ice is melting at a faster rate than last year, despite a cold winter, according to new data released yesterday by the US National Snow and Ice Data Centre (NSIDC).
Figures show that 2008 began with ice covering a larger area than at the beginning of last year. Since then, however, the levels have shrunk to what they were last June, a record-breaking period for sea-ice loss. Researchers say that much of the ice is so thin it melts easily, and that previous forecasts for an ice-free Arctic during the summer season may now have to be brought forward drastically.
Julienne Stroeve, a research scientist at the NSIDC, said: "We had a bit more ice in the winter, although we were still way below the long-term average. So we had a partial recovery.
"But the real issue is that most of the pack ice has become really thin, and if we have a regular summer now it can just melt away."
In March, Nasa reported that the area covered by sea ice was slightly larger than in 2007, but much of it consisted of thin floes that had formed during the previous winter. These are much less robust than thicker, less saline floes that have already survived for several years.
Only a few years ago, scientists were predicting ice-free Arctic summers by about 2080. Now, that day could arrive within a generation.
Last summer saw the levels of Arctic sea ice shrink to the smallest extent yet recorded, down to 4.2 million sq km from 7.8 million sq km in 1980.
Dr Stroeve said: "I think we're going to beat last year's record melt, though I'd love to be wrong.
"If we do, then I don't think 2013 (the year when the Arctic could be ice-free in summer] is far off anymore. If what we think is going to happen does happen, then it'll be within a decade anyway."
From a climate point of view, the melt could bring global impacts accelerating the rate of warming and the rising of the sea level.
Dr Ian Willis, of the Scott Polar Research Institute in Cambridge, said: "This is a positive feedback process. Sea ice has a higher albedo (reflectivity] than ocean water, so as the ice melts the water absorbs more of the sun's energy and warms up more, and that in turn warms the atmosphere more – including the atmosphere over the Greenland ice sheet."
Greenland is already losing ice to the oceans, contributing to the gradual rise in sea levels. The icecap holds enough water to lift sea levels globally by about seven metres, were it all to melt.
Because ice reflects more heat than water, as more ice melts the sea could get warmer, speeding up global warming and causing more ice to melt.
Natural climatic cycles, such as the Arctic Oscillation, play a role in year-to-year variations in ice cover, but Dr Stroeve believes the sea ice is now so thin that there is little chance of the melting trend turning round.
"If the ice were as thin as it was in the 1970s, last year's conditions would have brought a dip in cover, but nothing exceptional," she added. "But now it's so thin that you would have to have an exceptional sequence of cold winters and cold summers in order for it to rebuild."
The Arctic is already heating up at a faster rate than many other parts of the Earth's surface. While average temperatures on the planet rose by about 0.6C since 1900, the regional temperatures of the Arctic have risen by 2-3C.
How much worse is it all going to get?
What has gone wrong?
Sea ice, which floats on the surface of the ocean, naturally expands in coverage each winter and recedes in summer, but there has been a significant overall loss recorded during the past three decades. Most specialists agree that, as more ice is lost in summer, the Arctic is liable to heat up faster – instead of solar energy being reflected from the surface of the white ice, it is absorbed by the open, darker ocean, leading to even more melting of the ice.
What other repercussions could this trend have?
The dramatic shrinkage, should it continue, may speed up the melting of Arctic permafrost by up to 3.5 times, potentially damaging the environment for plants, animals, and humans by releasing billions of tonnes of carbon dioxide and methane.
Is the sea ice in danger of disappearing altogether?
Some computer models used by the UN's Intergovernmental Panel on Climate Change predict the Arctic will be virtually ice-free by summer 2070. More pessimistic forecasts suggest that this may happen within five to ten years.
How will it affect polar bears?
Given they rely on ice floes for shelter, hunting and breeding, they are already suffering. Scientists have documented significant weight loss among pockets of the species, and a decline in birth rates among bears in certain regions.