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US-Netherlands Research Finds Greenland and Western Antarctica Icecaps Melting at Approximately Half the Speed Previously Expected

The Greenland and West Antarctic ice caps are melting at half the speed previously predicted, according to research by a joint US/Dutch team from the Jet Propulsion Laboratory, TU Delft and SRON Netherlands Institute for Space Research. The scientists have published their findings in the September issue of Nature Geoscience.

The corrections for deformations of the Earth’s crust have a considerable effect on the amount of ice that is estimated to be melting each year. We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted.

—Dr. Bert Vermeersen of TU Delft

The average rise in sea levels as a result of the melting ice caps is also lower.

The melting of the ice caps has been charted since 2002 using the measurements produced by the two GRACE satellites. (Earlier post.) From space they detect small changes in the Earth’s gravitational field. These changes are related to the exact distribution of mass on Earth, including ice and water. When ice melts and lands in the sea, this therefore has an effect on the gravitational field.

“Gravity measurements of the ice-mass loss in Greenland and Antarctica are complicated by glacial isostatic adjustment. Simultaneous estimates of both signals confirm the negative trends in ice-sheet mass balance, but not their magnitude.”
—Bromwich and Nicolas

Based on this principle, previous estimates for the Greenland ice cap calculated that the ice was melting at a rate of 230 gigatonnes a year (i.e. 230,000 billion kg). That would result in an average rise in global sea levels of around 0.75 mm a year. For West Antarctica, the estimate was 132 gigatonnes a year.

However, these results were not properly corrected for glacial isostatic adjustment, the phenomenon that the Earth’s crust rebounds as a result of the melting of the massive ice caps from the last major Ice Age around 20,000 years ago. These movements of the Earth’s crust have to be incorporated in the calculations, since these vertical movements change the Earth’s mass distribution and therefore also have an influence on the gravitational field.

Researchers from the Jet Propulsion Laboratory in Pasadena (US), TU Delft and SRON Netherlands Institute for Space Research have now succeeded in carrying out that correction far more accurately. They did so using combined data from the GRACE mission, GPS measurements on land and sea floor pressure measurements. These reveal that the sea floor under Greenland is falling more rapidly than was first thought.

The innovative aspect of our method is that we simultaneously matched the current changes in the ice mass and glacial isostatic adjustment to the observations, instead of assuming that a particular glacial isostatic adjustment model is correct. For Greenland in particular, we have found a glacial isostatic adjustment model that deviates rather sharply from general assumptions. But at present there are too few data available to verify this independently. A more extensive network of GPS readings in combination with geological indicators for the local and regional changes in sea level changes around Greenland over the last 10,000 years, will possibly be able to provide conclusive evidence on this matter in the years to come.

—Dr. Bert Vermeersen

Resources

  • Xiaoping Wu et al. (2010) Simultaneous estimation of global present-day water transport and glacial isostatic adjustment. Nature Geoscience 3, 642 - 646 doi: 10.1038/ngeo938

  • David H. Bromwich and Julien P. Nicolas (2010) Sea-level rise: Ice-sheet uncertainty. Nature Geoscience 3, 596 - 597 doi: 10.1038/ngeo946

Comments

HarveyD

Shaving off up to 10,000 ft of ice from Greenland and South Pole areas and redistributing this melted snow over the oceans will certainly have major effects on the globe's shape. It is surprising to note that scientists have not fully accounted for that phenomena before. As the globe crust bulges out where the thick ice was before, how much will it sink somewhere else? Will current low lands sink below ocean surface? If so, low lands will get a double hit, i.e. higher sea water level + sinking land level.

Arne

HarveyD,

The scientist did account for this, but it is inherently difficult to separate the two signals. Apparently this team have succeeded in increasing the accuracy which is a good thing.

Reel$$

What we must know is this study is NOT bad for the environment. Simply because we have overestimated the melt in Greenland and West Antarctic does not mean we can fire up more coal plants. Or continue drilling deep water wells. Ripping up landscape with mountain top removal and strip mines is NOT acceptable when we have viable alternative energy. Catastrophic oil spills are NOT acceptable.

Antarctic is where 90% of all ice and 80% fresh water on Earth resides. We are fortunate that while there is melting in the West, the East Antarctic nearly four times the size, is growing.

What we learn is that there are reasons other than gloom and doom to evolve to less damaging forms of energy production and use. They are hard economic and social reasons. And they affect and motivate both the political left and right.

ai_vin

Another thing to note is that although this team have succeeded in increasing the accuracy they've also left the door open for more with this quote: "But at present there are too few data available to verify this independently. A more extensive network of GPS readings in combination with geological indicators for the local and regional changes in sea level changes around Greenland over the last 10,000 years, will possibly be able to provide conclusive evidence on this matter in the years to come."

HarveyD

Tracking Ice cover changes will be easier with current and future higher accuracy satellites. However, changes over the last 10,000 years can only be done on the ground. Interpolation with short term data is risky. One thing is certain, ice has been melting very fast (with few exceptions) for the last 30+ years. Will this trend go on for the next 30+ years? If it does, it may not be the best time to invest in lower land areas.

Will S

Notice they said "But at present there are too few data available to verify this independently."

ejj

Reel$$ Wrote: "Simply because we have overestimated the melt in Greenland and West Antarctic does not mean we can fire up more coal plants. Or continue drilling deep water wells. Ripping up landscape with mountain top removal and strip mines is NOT acceptable when we have viable alternative energy. Catastrophic oil spills are NOT acceptable."

@Reel$$: I know where you are coming from but do you want to go down to Brazil and shut down Petrobras then?
Sept 3, 2010 Petrobras Plans to Raise $75 Billion in Biggest Sale http://www.businessweek.com/news/2010-09-03/petrobras-plans-to-raise-75-billion-in-biggest-sale.html "Petroleo Brasileiro SA, Latin America’s largest company by market value, plans to raise as much as 129 billion reais ($75 billion) in the world’s largest share sale as it seeks cash to develop offshore oil fields. The shares rose 4.4 percent for the biggest gain since May." Petrobras is going to raise $75 BILLION for OFFSHORE DRILLING...FOR CRUDE.


ejj

If no one is going to stop Petrobras from spending $75 Billion for offshore drilling, does that mean the US should stop? It's like disarming unilaterally because you don't like war, and want to send the message to other countries that they should disarm too --- but do you think they are really going to listen to you?

ejj

Don't forget who is bankrolling massive amounts of investments in Brazil --- China. A lot of the new energy extracted from Brazil, both onshore and offshore, will undoubtedly go straight to China.

FACTBOX-China's surging direct investment in Brazil
http://www.foxbusiness.com/markets/2010/08/10/factbox-chinas-surging-direct-investment-brazil/

Reel$$

"I know where you are coming from but do you want to go down to Brazil and shut down Petrobras then?"

Apparently it would be more effective to go to Beijing for this mission. No. I don't have to convince the Chinese they have a petroleum addiction. They'll figure it out on their own.

But I might point out that just one big blowout cost BP at least $$40 Billion in losses. That's a whole year's worth of profits. Not a very smart investment after all.

ejj

Reel$$ Wrote: "But I might point out that just one big blowout cost BP at least $$40 Billion in losses. That's a whole year's worth of profits. Not a very smart investment after all."

@Reel$$: Actually I'm thinking offshore drilling is an incredibly smart investment. 2 major offshore well accidents in what - 40 years? How much revenue has been generated, how many jobs created, how many tax dollars put into government coffers over that amount of time? It's pretty ridiculous to say they are viable options for the masses with which to replace oil when its obvious there aren't (ie. $40k Chevy Volt, $30k home solar power arrays). To force America off oil without truly viable options would erode our national security.

HarveyD

ejj, there are other options. Our oil addiction was created by we know who and we will have to wean ourselves within 2 or 3 decades. By that time (and before) very high efficiency electrified vehicles will be mass produced and common place every where.

Producing more clean electricity is not a major challenge. All technologies required exist already. Nuclear, Wind, Sun, Hydro etc can produce many times more clean e-energy than we require.

Will the transition take 10, 20, 30 or 40 years?

Will USA continue to import 66% of the crude oil used and for how long?

We have a choice to make. We could start with one e-car + (XX) improved ICE vehicles per family and a few years latter progress to 2 e-cars etc. Fuel consumption would go down quickly enough and crude oil imports too.

Reel$$

ejj,

It's pretty ridiculous to say they are viable options for the masses with which to replace oil when its obvious there aren't (ie. $40k Chevy Volt, $30k home solar power arrays).

Where some see impossible challenges - we see excellent opportunity. Both the Volt and Leaf offer $350/month lease programs. The problem right now is there will not be enough EVs made to meet demand over the next three years. But it IS A START.

Increasing efficiency from PV, rapidly dropping costs for Li-ion batteries, 11 major manufacturers announced EVs/PHEVs. Why pay $3.25 for gas at 35mpg when you can get 80mpg equivalent from an EV?? Waste to alcohol/biodiesel, algae, wind, wave, hydro, coal2NG conversion, distributed CHP, SOFCs... all opportunities.

Is this transition huge?? Yes. Will it take 20 years? Yes. Are there viable alternatives right now? Taken as a collective portfolio, yes. The single most effective act comes from electrification of transport. Accelerating progress with conventional science behind us will accomplish our goals.

Because the game would be no FUN if we unveil new physics now would it?

sheckyvegas

What the hell do they mean the Earth's crust "rebounds"? Rebounds from what? 20,000 years of ice?
Uh-uh, I know what's going on. I saw that movie!
WE ALL GONNA DIE! SAVE ME, JOHN CUSACK!

ai_vin

Latest data shows that this study was premature;
http://www.jpl.nasa.gov/news/news.php?release=2012-376&cid=release_2012-376

November 29, 2012

PASADENA, Calif. - An international team of experts supported by NASA and the European Space Agency (ESA) has combined data from multiple satellites and aircraft to produce the most comprehensive and accurate assessment to date of ice sheet losses in Greenland and Antarctica and their contributions to sea level rise.

In a landmark study published Thursday in the journal Science, 47 researchers from 26 laboratories report the combined rate of melting for the ice sheets covering Greenland and Antarctica has increased during the last 20 years. Together, these ice sheets are losing more than three times as much ice each year (equivalent to sea level rise of 0.04 inches or 0.95 millimeters) as they were in the 1990s (equivalent to 0.01 inches or 0.27 millimeters). About two-thirds of the loss is coming from Greenland, with the rest from Antarctica.

This rate of ice sheet losses falls within the range reported in 2007 by the Intergovernmental Panel on Climate Change (IPCC). The spread of estimates in the 2007 IPCC report was so broad, however, it was not clear whether Antarctica was growing or shrinking. The new estimates, which are more than twice as accurate because of the inclusion of more satellite data, confirm both Antarctica and Greenland are losing ice. Combined, melting of these ice sheets contributed 0.44 inches (11.1 millimeters) to global sea levels since 1992. This accounts for one-fifth of all sea level rise over the 20-year survey period. The remainder is caused by the thermal expansion of the warming ocean, melting of mountain glaciers and small Arctic ice caps, and groundwater mining.

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