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.
Thanks for the ping.
I think it's interesting that the scientific measuring device referenced in post #96 which, according to its promotional website,
I'm not sure; I think ocean expansion is the dominant term.
I was just noticing the same thing; that the data is actually VERY linear for the last ten years.
This data does answer some of my earlier questions. However, in the last 10 years, China's manufacturing base has grown immensely and India has grown a middle class. You'd think that the corresponding increase in fossil fuel consumption would cause the rate of sea level rise to increase. However, it has stayed very linear for all ten years. (Yes, I know how to read a graph, and I understand that the trendline is linear by design. I'm not talking about the trendline, I'm talking about the data that feeds into the trendline, which does not seem to visually depict an increasing rate of sea level rise.)
It couldn't be the the satellite that's de-orbiting at a rate of 3mm per year, could it? :)
Either way, this data purports to prove that sea levels are rising by about an inch a year. That's nice. My continental plate is shifting at about two inches per year or more. Why exactly should I go all hysterical over changing sea levels when I'm already totally complacent about tectonic shift?
I'm not just trolling here. I'm dead serious. Plate tectonics simply does not affect my day-to-day existence. I don't get freaked out at the prospect that my coastline might be two inches further to the west this year than it was last year - and my office building is fifty feet away from the waterline of Puget Sound. If the magnitude of the change to my environment that I might expect as a result of global sea level rise is one-twentieth that of the year-to-year change I experience anyway, then why exactly should I care? Why should anyone?
By averaging numerous multiple measurements (rather than a single measurement good to +/- 5 cm) the long-term sea level rise can be extracted from the data. The satellites are on an exact repeat orbital cycle, meaning that they pass over the exact same places every 10 days (I think it's a 10-day cycle, that could be incorrect). So by measuring repeatedly, the other variable factors average out, leaving the long-term trend.
"How they weigh pigs at UC-Berkeley"? Hmm. This sounds juicy. What's that?
Whether you choose to believe it or not, the "ruse" was that "Iceland" was actually a relatively nice place to be, with geothermal vents for natural heating, good access to abundant fishing grounds, and enough arable soil to sustain crops. Greenland however, had none of these.
Fearing word would get back to Europe about a new land that held promise, he chose to name the icy-hell "Greenland" and the promising territory "Iceland" - exact opposites of what they were - hoping that prospective raiders would first chose to go to "Greenland", and seeing how unwelcoming it was, would shun exploring "Iceland" all together.
Basically, he wanted them to think that if Vikings considered Greenland to be Green, then you could imagine how bad a place Vikings called Iceland would be.
I don't think there's much consensus when you break down the elements. The CO2 is only agreed to add about a degree C but there are other AGW advocates who talk about more without being very quantitative. The water vapor feedback doesn't bring much consensus since the models break down into parameters like albedo that aren't going to be generally agreed on. Each time you peel back another layer from other GH gasses to various other feedbacks, there's plenty of disagreement about physical processes involved.
The problem with reading certain sites like RC is they don't want to admit that the underlying uncertainties can invalidate their preconceived conclusions.
It works like this:
FIRST, find a FULCRUM and a long, strong LEVER.
SECOND, move the LEVER on the FULCRUM until the two sides are in EXACT balance.
THIRD, place the pig in the middle of one side of the LEVER.
(Note: this process works best if the pig is "docile". Since you will probably find it necessary to "relax" the pig with a gallon of two-buck-chuck, remember that a gallon is 128 ounces).
FOURTH, place a stone on the OTHER side of the LEVER.
FIFTH, move the stone towards the FULCRUM or away from the FULCRUM until the pig-side and the stone-side are in EXACT balance.
SIXTH, measure the distance of the pig (= Dp) from the FULCRUM EXACTLY and measure the distance of the stone (= Ds) from the FULCRUM EXACTLY. (Note: Measuring to the nearest millimeter will enhance accuracy.)
SEVENTH, guess the weight of the stone (= Ws)
EIGHT, the weight of the pig (Wp) may be calculated with FOUR-DIGIT-PRECISION using the following equation:
Wp = [(Ws x Ds)/Dp] - 128 ounces
This method has never failed to produce an answer at UC-B.
You said,
"By averaging numerous multiple measurements (rather than a single measurement good to +/- 5 cm) the long-term sea level rise can be extracted from the data."
I think that is the "conventional wisdom" -- but it defies logic.
An "average" of CRUDE numbers is not by the process of "averaging" made into a PRECISE number.
I understand that "professional" statisticians have a different opinion based on what they ASSUME are standard data populations, standard deviations etc.
But, IMHO, that self-promoting opinion is wrong...
My impression is that sea level is all about wind. There are seasonal and cyclical changes as the prevailing winds change. Finally the weather pattern changes as a result of global warming will change the winds and sea level measurements. The average sea level can't be based on equally spaced measurements. There may not be such a thing as average sea level, just various biased local measurements where it is necessary to understand the biases.
I think this is good news for all the Greenlandians.
I sure hope this doesn't mean I have to move back to Ohio.
You Win!
Looks good for my ocean front property in south central Indiana. I should get busy building the dock now.
Okay, class, did you see how fast he figured that out? Bueler? Baahuuuulerrrrr?
I do. Just razzing you.
When I say it is the speed of the melting I meant he acceleration. Indeed 60 u miles is irrelevant. But if the melting continues to increase exponentially then we quickly achieve as signficant amount.
I totally ignored it because it is a scare tactic and ludicrous. If we get to the point where the rise in the ocean levels will dramatically affect our civilization we are going to be pretty far gone anyway.
The biggest issue with the Greenland ice sheet is its capacity to dramatically alter the Gulf Stream. The measurements of the melting ice are far more accurate and can be visibly observed via satellite photos.
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