December 16, 2008

Arctic Has Lost 2 Trillion Tons Of Land Ice In 5 Years

Recently-reported NASA satellite data shows that Greenland, Antarctica and Alaska have shed more than 2 trillion tons of land ice since 2003.

Scientists said the data collected by NASA's GRACE satellite show signs of global climate change.

NASA geophysicist Scott Luthcke said more than half of the loss of landlocked ice in the past five years has occurred in Greenland, based on measurements of ice weight. That's enough melted water to fill up about 11 Chesapeake Bays, he said, and the Greenland melt seems to be accelerating.

While this year's ice melt wasn't as severe as last year's, Luthcke said the results are still noteworthy.

NASA had planned on presenting the findings on Thursday at the American Geophysical Union conference in San Francisco, but summer figures for Greenland have yet to be completed.

Meanwhile, in Alaska land ice increased slightly in 2008 because of large winter snowfalls, Luthcke said. Alaska has lost 400 billion tons of land ice since the satellite began taking measurements in 2003.

In the 1990s, Greenland didn't add to world sea level rise; now that island is adding about half a millimeter of sea level rise a year, NASA ice scientist Jay Zwally said.

Luthcke said ice melting in Greenland, Antarctica and Alaska has caused global sea levels to rise about one-fifth of an inch in the past five years.

"It's not getting better; it's continuing to show strong signs of warming and amplification," Zwally said. "There's no reversal taking place."

Scientists believe they are seeing signs of the so-called Arctic amplification effect, which causes the Arctic to warm faster than predicted.

As sea ice melts, the Arctic waters absorb more heat in the summer, having lost the reflective powers of vast packs of white ice. That absorbed heat is released into the air in the fall. That has led to autumn temperatures in the last several years that are six to 10 degrees warmer than they were in the 1980s, said research scientist Julienne Stroeve at the National Snow and Ice Data Center in Boulder, Colo.

"The pace of change is starting to outstrip our ability to keep up with it, in terms of our understanding of it," said Mark Serreze, senior scientist at the National Snow and Ice Data Center in Boulder, Colo., a co-author of the Arctic amplification study.

Two other studies to be released at the conference will show evidence that Arctic thawing is releasing methane - the second most potent greenhouse gas.


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