Arctic ice 'could be gone in five years'
By agencies
Published: 5:01PM GMT 12 Dec 2007
An iceberg melts off Ammassalik Island in Eastern Greenland
The hot Northern Hemisphere summer sharply increased the rate at which Arctic ice is melting and scientists now believe summer ice could be gone completely within five years.
Australia lands commercial jet on Antarctic ice
New Nasa satellite images reveal so much ice has disappeared that an irreversible tipping point has already been reached because of global warming.
The volume of Arctic sea ice at the end of last summer was half what it was four years ago and that the Greenland ice sheet lost almost 19bn tonnes of its volume - more than ever before.
"The Arctic is screaming," said Mark Serreze, senior scientist at the US government's Snow and Ice Data Centre in Colorado.
And Nasa climate scientist Jay Zwally said: "At this rate, the Arctic Ocean could be nearly ice-free at the end of summer by 2012, much faster than previous predictions."
He added: "The Arctic is often cited as the canary in the coal mine for climate warming. Now as a sign of climate warming, the canary has died. It is time to start getting out of the coal mines."
What happens in the Arctic has implications for the rest of the world. Faster melting there means eventual sea level rise and less sea ice means more immediate changes in winter weather.
More than 18 scientists told the Associated Press they were surprised by the level of ice melt this year.
"I don't pay much attention to one year... but this year the change is so big, particularly in the Arctic sea ice, that you've got to stop and say, 'What is going on here?' You can't look away from what's happening here," said Waleed Abdalati, Nasa's chief of cyrospheric sciences. "This is going to be a watershed year."
2007 shattered records for Arctic melt in the following ways:
552 billion tons of ice melted this summer from the Greenland ice sheet, according to preliminary satellite data to be released by Nasa. That is 15 per cent more than the annual average summer melt, beating 2005's record.
A record amount of surface ice was lost over Greenland this year, 12 per cent more than the previous worst year, 2005, according to data the University of Colorado. That is nearly quadruple the amount that melted just 15 years ago. It is an amount of water that could cover Washington, DC, a half-mile deep, researchers calculated.
The surface area of summer sea ice floating in the Arctic Ocean this summer was nearly 23 per cent below the previous record. The dwindling sea ice already has affected wildlife, with 6,000 walruses coming ashore in northwest Alaska in October for the first time in recorded history.
Still to be released is Nasa data that shows the remaining Arctic sea ice to be unusually thin, another record. That makes it more likely to melt in future summers. Combining the shrinking area covered by sea ice with the new thinness of the remaining ice, scientists calculate that the overall volume of ice is half of 2004's total.
Alaska's frozen permafrost is warming, although not quite thawing yet. Temperature measurements 66 feet deep in the frozen soil rose nearly four-tenths of a degree from 2006 to 2007, according to measurements from the University of Alaska. While that may not sound like much, "it's very significant," said University of Alaska professor Vladimir Romanovsky.
Greenland, in particular, is a significant bellwether. Most of its surface is covered by ice. If it should melted, which scientific experts think probably would take centuries, not decades, it could add more than 22 feet to the world's sea level.
However, for almost the past 30 years, the data pattern of its ice sheet melt has zigzagged. A bad year, like 2005, would be followed by a couple of lesser years.
According to that pattern, 2007 should not have been a major melt year, but it was, said Konrad Steffen, of the University of Colorado, which gathered the latest data.
"I'm quite concerned," he said. "Now I look at 2008. Will it be even warmer than the past year?"
Other new data, from a Nasa satellite, measures ice volume. Nasa geophysicist Scott Luthcke, reviewing it and other Greenland numbers, concluded: "We are quite likely entering a new regime."
Melting of sea ice and Greenland's ice sheets also alarms scientists because they become part of a troubling spiral.
White sea ice reflects about 80 per cent of the sun's heat away from Earth, Nasa's Zwally said. When there is no sea ice, about 90 per cent of the heat goes into the ocean which then heats up everything else. Warmer oceans then lead to more melting.
"That feedback is the key to why the models predict that the Arctic warming is going to be faster," Zwally said. "It's getting even worse than the models predicted."
Nasa scientist James Hansen, the lone-wolf researcher often called the godfather of global warming, will tell scientists and others at a meeting of researchers in California on Thursday that in some ways Earth has hit one of his so-called tipping points, based on Greenland melt data.
"We have passed that and some other tipping points in the way that I will define them," Hansen said in an email. "We have not passed a point of no return. We can still roll things back in time - but it is going to require a quick turn in direction."
Last year, Cecilia Bitz at the University of Washington and Marika Holland at the National Centre for Atmospheric Research in Colorado startled their colleagues when they predicted an Arctic free of sea ice in just a few decades. Both say they are surprised by the dramatic melt of 2007.
Bitz, unlike others at Nasa, believes that "next year we'll be back to normal, but we'll be seeing big anomalies again, occurring more frequently in the future." And that normal, she said, is still a "relentless decline" in ice.
http://www.telegraph.co.uk/earth/earthn ... years.html
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