Posted on 08/11/2006 10:49:56 AM PDT by cogitator
The Greenland ice sheet is melting three times faster today than it was five years ago, according to a new study.
The finding adds to evidence of increased global warming in recent years and indicates that melting polar ice sheets are pushing sea levels higher, the authors report.
According to the study, Greenland ice loss now amounts to more than 48 cubic miles (200 cubic kilometers) each year.
"Significant melting has a significant impact on sea level rise," said Jianli Chen, a research scientist at the University of Texas at Austin who led the study.
The finding, reported today by the online edition of the journal Science, closely agrees with another study on the rapid wasting of Greenland's glaciers published in the journal in February.
Both studies suggest the shrinking ice sheet now contributes about 0.02 inch (0.5 millimeter) a year to global sea level rise.
"That's a very big number," Chen said.
Losses and Gains
Global sea levels have risen by about 0.1 inch (2.8 millimeters) a year over the past decade.
If all the ice on Greenland were to melt into the North Atlantic Ocean, global sea levels would rise by about 21.3 feet (6.5 meters).
Thus scientists are keen to understand if the Danish-owned Arctic island (Greenland map) is losing more ice mass through melting and discharge of glaciers than it is gaining from fresh snowfall.
Richard Alley is a glaciologist at Pennsylvania State University in University Park who was not involved with the study.
He says the new study fits well with other recent studies showing a Greenland meltdown.
"It really does appear that the ice sheet is losing mass," he said in an email.
"Looking at the history of these measurements, the ice sheet was probably near balance a couple of decades ago and has begun shrinking recently," he continued.
"This parallels recent warming."
Full of GRACE
The new study is based on an analysis of gravity measurements collected by a pair of twin wedge-shaped satellites that orbit the Earth in tandem.
The satellites are part of the Gravity Recovery and Climate Experiment (GRACE), which was launched in March 2002 and is run by a team of experts in the U.S. and Germany.
GRACE measures landmass based on its gravitational pull. The denser a region is, the stronger its pull and the faster the satellites will move above it.
The satellites are separated by a distance of 137 miles (220 kilometers) when they are in stable orbit. As the front satellite crosses over an area of strong gravity, it speeds up, increasing the distance between the two satellites.
"Any tiny change in the distance can be used to infer the surface mass change," Chen said.
Liquid water is generally denser than ice and so has a stronger gravitational pull.
Chen and his University of Texas colleagues analyzed the gravity measurements over Greenland between April 2002 and November 2005, separating the mass change from other signals.
The team found that Greenland is now losing between 52 and 63 cubic miles (216 and 262 cubic kilometers) of ice mass each year.
The current wasting is about three times the rate gleaned from an earlier study of the first two years of GRACE data.
Jay Zwally is a glaciologist with the NASA Goddard Space Flight Center in Greenbelt, Maryland.
He agrees that Greenland ice loss has accelerated in recent years.
But based on he and his colleagues' unpublished analysis of the latest GRACE data, he believes the current ice loss rate is less than half what Chen's team reports.
Nevertheless, he says, Greenland does appear to be losing more ice mass than it gains.
"I would say Greenland now is beginning to contribute significantly to sea level rise," Zwally said. "There's been a significant change in a relatively short period of time."
As methods for analyzing GRACE data are refined and combined with other techniques, scientists will reach agreement over just how quickly the continent is wasting away, Zwally adds.
Historical Perspective
GRACE has only been orbiting Earth for three and a half years, not long enough to determine if the increase in melting is due to global warming or natural variability, the University of Texas's Chen says.
Longer term trends, and confidence in data interpretation, must wait until several more years of data are collected, he says.
According to Alley, the Pennsylvania State glaciologist, increasing snowfall, increasing melting, and increasing flow of glaciers into the ocean are all expected to result from global warming.
Historical analyses indicate that Greenland shrank when changes in Earth's orbit gave more summer sunshine to the island a few thousand years ago and about 130,000 years ago, he says.
"History and physics and recent observations tie warming to ice shrinkage," he said.
And projections of future climate change indicate continued warming over Greenland if greenhouse gas emissions remain unchecked.
"So shrinkage seems likely," Alley said.
Just because people disagree with me at Frdoesn't mean I give in. No respetable Freeper does. You appear to have been around here long enough to know that.
The is no legitimate debate about whether the climate is changing. Temperatures have risen over the last century and they are still rising. Denying this is to deny completely convincing scientific and observational evidence. To say "well it was perty darn cold this winter where I live" is to show complete ignorance of the issue.
The only real issue is whether humans are contributing to climate change to such an extent that we need to alter the behaviour to prevent the change from becoming too extreme.
It is a good debate. At FR those who say "no" are in the majority. In the real world, they are vastly outnumbered and losing quickly as policy takes shape and changes are made.
Dismissing CO2 as too small a portion of total greenhouse gasses is to misunderstand that we are talking about an issue of balance. If you have a balance scale and alter the balance by one percent, the scale will tip. That is the correct analogy, although the earth also has feedback mechanisms to bring itself back into balance. The time scales of these mechanisms, however are usually different from human time horizons. Talking about warming on Mars is absurd sophistry and true junk science.
In pure political terms, people see their weather changing. They see an inefficient use of resources. They see people getting fat because they live unnaturally. Something seems out of whack and politicians(at the moment on led by the left, but increasingly not) backed by scientists are giving them a cause for the change which they can effect.
By dropping the ball on the issue, the right is giving the left a huge chance to implement unnecessarily expensive and command and control solutions that will do untold harm and probably be less effective than a conservative solution.
Yes, this will be expensive, but it wil primarily be expensive for the big CO2 emitters which happen to currently be the richest and most powerful companies and individuals in the world. When they have to begin paying start-ups for clean energy and products, it will cost them money. If the US sits on its hands too long and continues to let the Germans and Japanese race ahead, the money will go to companies from those countries. Or, America can develop the technology and export it.
So there you go. Whether you accept the science or not, the momentum is such that it makes sense to propose legitimate solutions to reducing CO2 output. If it concurently reduces reliance on foreign oil, so much the better for security.
There's a lot of hockey stick mentality in that statement. But Greenland's temperatures http://www.ferdinand-engelbeen.be/klimaat/greenland_temp.html are much more a function of the jet stream (NAO) than any worldwide increase and are just now catching up to the 1930's.
The ONLY reason this is so is because the climate is constantly changing. Whether those changes represent a long-term trend is an entirely different story.
Witness the numerous and sensationalist articles from the 80's claiming the Earth was headed into a new Ice Age..
The fact is that a) no one knows the reasons for any current trend with any certainty and b) no one knows how long the current trend will continue. More research is needed before extremely difficult and expensive decisions are made.
Waiting isn't such a bad option, since our overall store of science and engineering knowledge is increasing exponentially right now. Odds are we'll have a much better solution available by the time we figure all this out than we do now.
Maybe Ice looks Green in the right light.
The information is available. Significant factors such as solar flare fluctuations, rotating hot spots in the earth's core, modulations in earth orbit, molecule exchanges (co2 in particular) between the ocean and atmosphere, volcanic activity (land and oceanic), etc. all have been cited as having effects on climate change. You just have to look for it. The only power that the global warming and "caused by human activity" theory has is the conventional wisdom created by the MSM and radical groups that live off the funding that it self-perpetuates.
touche
I'm not claiming Greenland did not have a warm period. I am stating the origin of the name.
" "A three-to-four degree increase of the temperature on Greenland from 1920 to 1930, and the increase recorded since 1995 has sped up the ice melt," he said."
Documenting that things changed in the past doesn't refute that there are changes happening now, and the concern is that the changes are happening more rapidly.
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