2008-12-17 08:52:07
Tue Dec 16, 7:10 am ET
WASHINGTON More than 2 trillion tons of land ice in Greenland, Antarctica and
Alaska have melted since 2003, according to new NASA satellite data that show
the latest signs of what scientists say is global warming.
More than half of the loss of landlocked ice in the past five years has
occurred in Greenland, based on measurements of ice weight by NASA's GRACE
satellite, said NASA geophysicist Scott Luthcke. The water melting from
Greenland in the past five years would fill up about 11 Chesapeake Bays, he
said, and the Greenland melt seems to be accelerating.
NASA scientists planned to present their findings Thursday at the American
Geophysical Union conference in San Francisco. Luthcke said Greenland figures
for the summer of 2008 aren't complete yet, but this year's ice loss, while
still significant, won't be as severe as 2007.
The news was better for Alaska. After a precipitous drop in 2005, land ice
increased slightly in 2008 because of large winter snowfalls, Luthcke said.
Since 2003, when the NASA satellite started taking measurements, Alaska has
lost 400 billion tons of land ice.
In assessing climate change, scientists generally look at several years to
determine the overall trend.
Melting of land ice, unlike sea ice, increases sea levels very slightly. 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 in a telephone interview from the conference.
Between Greenland, Antarctica and Alaska, melting land ice has raised global
sea levels about one-fifth of an inch in the past five years, Luthcke said. Sea
levels also rise from water expanding as it warms.
Other research, being presented this week at the geophysical meeting point to
more melting concerns from global warming, especially with sea ice.
"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 studying sea ice will announce that parts of the Arctic north of
Alaska were 9 to 10 degrees warmer this past fall, a strong early indication of
what researchers call the Arctic amplification effect. That's when the Arctic
warms faster than predicted, and warming there is accelerating faster than
elsewhere on the globe.
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.
That's a strong and early impact of global warming, she said.
"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 coming out at the conference assess how Arctic thawing is
releasing methane the second most potent greenhouse gas. One study shows that
the loss of sea ice warms the water, which warms the permafrost on nearby land
in Alaska, thus producing methane, Stroeve says.
A second study suggests even larger amounts of frozen methane are trapped in
lakebeds and sea bottoms around Siberia and they are starting to bubble to the
surface in some spots in alarming amounts, said Igor Semiletov, a professor at
the University of Alaska in Fairbanks. In late summer, Semiletov found methane
bubbling up from parts of the East Siberian Sea and Laptev Sea at levels that
were 10 times higher than they were in the mid-1990s, he said based on a study
this summer.
The amounts of methane in the region could dramatically increase global warming
if they get released, he said.
That, Semiletov said, "should alarm people."