An already relentless melting of the Arctic greatly accelerated this summer, a warning sign that some scientists worry could mean global warming has passed an ominous tipping point. One even speculated that summer sea ice would be gone in five years.
Greenland's ice sheet melted nearly 19 billion tons more than the previous high mark, and the volume of Arctic sea ice at summer's end was half what it was just four years earlier, according to new NASA satellite data obtained by The Associated Press.
"The Arctic is screaming," said Mark Serreze, senior scientist at the government's snow and ice data center in Boulder, Colorado.
Just last year, two top scientists surprised their colleagues by projecting that the Arctic sea ice was melting so rapidly that it could disappear entirely by the summer of 2040.
This week, after reviewing his own new data, 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..."SNIP
...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 percent of the sun's heat off Earth, NASA's Zwally said. When there is no sea ice, about 90 percent of the heat goes into the ocean which then warms everything else up. 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, on Thursday will tell scientists and others at a meeting of researchers in San Francisco 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 e-mail. "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."
http://www.cnn.com/2007/TECH/science/12/11/arctic.melt.ap/index.html
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