Monday, November 13, 2006

GRACE satellite results inconclusive

The SMH dug up a year old story (actually even older) about the GRACE satellite and presented it as today's news in order to cash in on the global warming scare. Heaven forbid they actually report NASA press releases when they are released! The release includes this interesting line:
“Although the ice mass loss observed in the new study is less than half of what other recent research has reported, the results show that Greenland is now losing 20% more mass than it receives from new snowfall each year.”
Another report mentions that:
“Continued monitoring in the future is needed to determine whether this ice loss is a long-term trend, the authors point out.”
That is good, I'd hate a brand new technique that measures something different (mass) from all other studies (height of ice sheet) would be touted as 'proof' of global warming after only 3 years of data are collected.

At the same time last year, the ESA were releasing research that showed the amount of ice on Greenland
“Scientists from the European Space Agency (ESA) recently analyzed 11 years of radar altimetry data for the Greenland Ice Sheet from its ERS satellites, and came up with a remarkable find. While the edges of the Greenland Ice Sheet have thinned, the high-elevation interior has actually grown in thickness as much as 6 cm (nearly 2.5 inches) per year, for the years 1992-2003. ”
Of course they must point out that this is consistent with global warming:
“We should expect that the increased snowfall produced by mild warming of the air mass over Greenland is only a temporary effect, however. As the computer models also indicate, once temperature increases exceed 3oC, new snowfall would not outpace the rate of melting, and the Greenland Ice Sheet would eventually melt away raising global sea level by as much as seven meters.”
Except that it's already melting away according to NASA, and we've had nowhere near a 3oC temperature increase. I guess they're still puzzling over that one ...

It seems that GRACE data presents some difficulties to global warming in other ways:
“A big complication in the GRACE measurement of the Antarctic ice sheet thickness is the fact that the land beneath is lifting, part of the “post-glacial rebound” after the last Ice Age, which ended only about 10,000 years ago (melting in Antarctica continued up until only about 4,000 years ago). The crust—the uppermost layer of Earth—floats on the rock beneath, which is plastic and responds to changes in its “load” (see last link). The melting of the huge ice age glaciers removed a large mass from Antarctica, and the continent is slowly lifting to reestablish equilibrium. The GRACE scientific team used geological estimates of ice thickness changes and a model of rock flow beneath Earth’s surface to estimate the uplifting of the land, which is a significant effect.

After taking into account all the above effects, the GRACE scientists find that from 2002 through 2005, the volume of the Antarctic ice sheet decreased substantially, corresponding to .4 mm plus or minus .2 mm of sea-level increase per year. This result was a surprise, both because of the extremely low temperatures in Antarctica, as mentioned above, and because forecasts of global warming had predicted increased snowfall in Antarctica.

In an earlier study, GRACE determined that the Greenland ice sheet is melting more rapidly than previously thought—in fact, the melting in Greenland and in Antarctica each produce about the same rate of sea level rise. So these ice sheets together add about .8 mm/yr. The overall rate of sea level rise over the last ten years, as obtained from statistical studies of radar measurements, is about 3 mm/year, and roughly half of this increase is due to thermal expansion of the oceans.

As the GRACE project continues, more data will accumulate and delineate the trend in ice sheet thickness over a longer time interval. Also, any change in the rate of melting would be unaffected by the correction for post-glacial rebound, which is presumed to be constant over long periods of time”
National Geographic reports that:
“The new study dates the start of accelerated melting to the spring of 2004 and finds the acceleration is confined to southern Greenland, Velicogna says.

"This leads us to think this [mass loss] is probably associated with ice discharge," Velicogna said.

Ice discharge—the dumping of glacial ice into the North Atlantic—is a process with built-in inertia, Velicogna says.

Even if temperatures suddenly drop in Greenland, she says, the discharge would continue for several years.

Velicogna adds that if the mass loss is indeed associated with warming global temperatures and temperatures continue to rise, the accelerated melting could spread to northern Greenland.

"We don't know for sure, but it could happen and is something to be watched for," she said. ”
Another bunch of NASA scientists knew in 2002 that gravity changes might not be climate related:
“Scientists believe movements of mass cause this recent change from the high latitudes to the equator. Such large changes may be caused by climate change, but could also be part of normal long-period climatic variation. "The three areas that can trigger large changes in the Earth's gravitational field are oceans, polar and glacial ice, and atmosphere," Cox said.”
Unfortunately that lab no longer exists, so finding our more about their research is a bit hard ...

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