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.
Yup, cold water will do that.
"You leave Pittsburgh traveling towards NYC. Your train is going 30mph. Ben R. leaves NYC traveling to Pittsburgh on his motorcycle (helmet on) going 88mph. Which traveler will cause more ice to melt in Greenland?"
Gary Coleman, of course. Next!
"Could it possibly be "SUMMER""
Uh, they have Summer every year in Greenland. This is a story about increased loss of the icepack.
You may not believe that increased climatic temperature is a human-cause thing. I don't either. However, I'm not ignoring what appears to be a fact...that the climate is warming, and that there will be effects caused by that.
Climate does not know about political sides, you see.
I suggest sending Mr. Gore there to personally investigate the problem and that he remain on the ground in Greenland coordinating international efforts until a proper solution can be found!
The unsustainable demographics of Europe and the pendng collapse of their nanny-state system of economic entitlements will cause a far, far greater disruption of European economy than a warmer, longer, wetter, more fertile growing season will.
The world is an unpredictible place. Even if all of the doomsayers about global warming are correct (and that's a very, very big "if"), the fact is that the world will continue to change, sometimes drastically, with or without human intervention. Sometimes it'll be climate change, sometimes it'll be a new disease, sometimes it'll be the development of a new kind of weapon, sometimes it'll be the detection of an Earth-bound asteroid.
It is suicide to overspecialize into a particular climate configuration, a particular geographic configuration, etc., and then try to exert Herculean effort to maintain that particular configuration for all eternity. Human beings are smart critters, and that intelligence gives us the capacity for survival through adaptability. I suggest you use it.
So, while you wring your hands and scream, "We have to DO SOMETHING!!!!!!!!!", I sit back and calculate the potential value of ocean-front real-estate holdings in West Virginia. All the money you spend on imposing restrictions on factories and power plants, you can instead spend on researching hardier foodcrops that will fare better in a wider variety of climactic conditions. That way, not only do you prepare yourself better for THIS potential crisis, but you also leave yourself in a better position for handling future potential crises as well.
"Climate does not know about political sides, you see."
No, but climatologists do.
It's been a long time since Greenland - other that a coastal strip - has been "Green"; the ice sheet covers around 80% most of the land mass, and formed in the since the late Pliocene or or early Pleistocene - roughly 1.6 million years ago.
The oldest ice currently present is around 110,000 years old, that's why cores of the sheet - some go down 3KM - are useful in determining the Earth's past climate.
There is no general consensus among climatologists regarding the cause of the apparent current warming trend.
That's great. We can farm Greenland pretty soon.
Wrong! It was cow flatuance. Greenland was overrun with cows back then.
I get the speed. It's 60 cu miles / year out of a total of 600,000. As for fresh water disrupting the gulf stream, that will take quite a bit more water to do that. If you assume 60 cubic miles is spread over 2000 by 1000 miles of atlantic, that's 2 inches of fresh water.
FReund, you were getting your neck-tie buttered the other day! How do you say, "glutton for punishment" in Deutsche?
But series, once the glaciers melt--then come the four-fanged, polar rake-snakes. I share your concern . . .
Snakes on a glacier!
Sweet... is there oil under there?
I think that would be .05 meter or just less than 2 inches.
Cool a couple of more years and I have beachfront property.....Yeehaaa!
Not only that, but if it was floating and then melted, the ocean level would...remain unchanged. This is because, according to the law of bouyancy, a floating object displaces it's own mass of water. Since melted ice *is* water, the level doesn't change. This also means that if the Arctic icecap melts, ocean levels won't change a bit.
However, the Greenland ice sheet and the Antarctic ice sheet are both on land and will cause ocean levels to rise if they melt. If the Antarctic sheet were to completely melt ocean levels would rise about 500 feet.
There isn't a consensus among climatologists that there exists a real warming trend.
When you've got field scientists whose continued grants from the NSF depend on them being able to find conclusive evidence of global warming, they will find it, and they will do so in a repeatable and peer-reviewable manner.
Take the claim, for example, that global sea levels have been consistently rising 0.1" per year. First of all, where on Earth, literally, did they perform measurements fine enough to detect a 0.1" fluctuation in a five-mile-deep ocean? Where on Earth did they find tectonic plates that move slower than 2" per year, thus introducing a margin of error over 20 times as large as the magnitude of their measuremented deltas? Second of all, how long has this "consistent" 0.1" rise been going on? Have the oceans consistently rise 0.1" per year for the last... erm... year? I'd be very interested to know what next year's measurements would report.
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