Greenland Ice Sheet is Melting Faster, Study Says

National Geographic ^ | 08/10/2006 | John Roach

[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.

[Old Professer]

.02 now. Which, they say is 3 times the rate 5 years ago; now, repeating that rate of increase each 5 years we see that we get: .06;.18;.54; 1.64; 4.02; 14.76; 44.28; 132.84 and we are only up to the year 2056 and the sea level is 11 feet higher.

Take it ten more years out and it is up by 99.6 feet.

[MineralMan]

I am not a climatologist, so I cannot answer any of your question regarding that science.

What I said was that there is no general consensus among climatologists about the cause of the current warming trend. What you asked has nothing to do with that statement.

Most climatologists appear to believe that there is a warming trend. The cause of that warming, however, is not known and there is no general agreement among climatologists regarding the cause.

[Omedalus]

Wasn't disagreeing with you. :)

Our statements aren't exactly mutually exclusive. A majority of climatologists agree that global warming is occurring, but a very sizeable minority either disagrees or believes we don't have enough evidence to make a scientifically justifiable assertion. Of the climatologists who believe in global warming, there is marked disagreement as to whether or not it has any relation to human activity.

[Mike Darancette]

According to the study, Greenland ice loss now amounts to more than 48 cubic miles (200 cubic kilometers) each year.

Imagine that, the volume of the Earth's Oceans is 1,370,000,000 (1.37 billion) cubic kilometers so the volume of the oceans is increasing by .0000146% each year minus of course the net amount of snow that falls on Greenland and doesn't return to the Ocean.

[MineralMan]

"Wasn't disagreeing with you. :)
"

OK. I understand now.

[RightWhale]

"That's a very big number," Chen said.

It would be if the 48 cubic miles showed up on his half-acre. Worldwide it is not impressive.

[colorado tanker]

There is actually some small-scale farming on Greenland now, for the first time since the Medieval Warm Period.

[cogitator]

I guess it couldn't be the VOLCANOS that made Greenland could it?

Nope. Nothing currently active. (Iceland is a different story! They do have subglacial eruptions there that melt a lot of water.)

[cogitator]

This is very bad news. You inability to grasp it only shows your ignorance of the subject.

I thought you knew me better than that, ERF.

[cogitator]

And Greenland will return the warm state it had between 900 to 1400 AD.

And a lot of other regions, too.

[eyedigress]

Greenland was a ruse created by Eric the Red.

[cogitator]

There is no general consensus among climatologists regarding the cause of the apparent current warming trend.

That's not accurate. The quantification of attribution between human (anthropogenic) causation and natural variability factors is still uncertain, though it is becoming progressively less so. The warming trend that has occurred since the mid-1970s does not appear to have significant causative factors other than greenhouse gas forcing.

[cogitator]

As for fresh water disrupting the gulf stream, that will take quite a bit more water to do that.

Warmer SST can disrupt deep-water formation, not just freshening of the surface layer (but you were talking about the Gulf Stream -- different subject).

Nice RC exchange yesterday, BTW.

[MineralMan]

I hate to say this, but...what part of "no general consensus" are you not understanding? Climatologists differ in their thinking about the cause of climate change.

Some believe there is a human-connection. Others don't. If there were a "general consensus," then you'd find a vast majority that held one view. That is not the case.

My statement stands.

[q_an_a]

gee wiz anyone who has read the history of Vikings and their travels and settlements before Columbus discovered Ameirca will find them in a warm Greenland - only to leave when it got to cold to sustain food.

[cogitator]

There isn't a consensus among climatologists that there exists a real warming trend.

There are very few dissenters from the majority view that there is.

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?

Satellite radar altimetry. Look up "TOPEX/Poseidon" and "Jason 1" with Google for explanation of the technique.

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?

(click image for a BIG version)

[cogitator]

Some believe there is a human-connection. Others don't. If there were a "general consensus," then you'd find a vast majority that held one view. That is not the case.

There is a significant (maybe not vast) majority that holds one view. There is a minority that doesn't hold that view. My statement stands, too.

[MineralMan]

"There is a significant (maybe not vast) majority that holds one view. "

Then there is no "general consensus." Look up the word "consensus."

I'm very careful with what I write.

[cogitator]

1 a : general agreement : UNANIMITY (the consensus of their opinion, based on reports...from the border -- John Hersey> b : the judgment arrived at by most of those concerned (the consensus was to go ahead)

I'll take (b) for $500.

[chipengineer]

Nice data; thanks.

The rate is still pretty small and does not seem to be increasing (at least at this scale).

How much is melting ice, and how much ocean expansion?