Princeton geoscientists report Greenland ice sheet melting rate is increasing

Nov 20, 2012 by Bob Yirka report
Isua Supracrustal Belt Isua, south-west Greenland. Credit: University of Washington.

(Phys.org)—Princeton geoscientists Christopher Harig and Frederik Simons have been applying new methods to study the amount of ice melt in the Greenland ice sheet. They report in a paper published in the Proceedings of the National Academy of Sciences that the rate is approximately 200 billion tons annually and is rising at a rate of approximately 9 billion tons per year.

The two used data from the twin satellites used in the Gravity Recovery and (GRACE) that orbit in tandem over the Earth. As they pass over the planet they measure very small differences in gravity between the two that correspond to the amount of mass below. In looking at data recorded during the period August 2002 to 2011, they were able to measure the changes in mass of the ice sheet that covers Greenland, which is second only to Antarctica in size.

The two found that by analyzing GRACE data very closely they could actually pinpoint the parts of the ice sheet that were changing and by how much. They noted for example, that for the year 2003 to 2004, the bulk of melting occurred along the eastern coast of the island nation, whereas over the following year it was centered in the northeast. Surprisingly, they found that even as the ice sheet as a whole was losing mass, some mass was gained in central Greenland. It's not known why this has happened, but it's possibly due to higher amounts of snowfall that might have occurred.

The melting of the is believed to be associated with rising , which in turn is believed by most scientists to be the result of increased amounts of carbon dioxide in the atmosphere due mainly to human pollutants. As the ice sheets melt, rise. By studying melting rates, scientists are able to provide better estimates on how much the sea will rise and when. Current estimates put at 0.1 inches per year. Using the numbers from their study, the researchers estimate that sea levels will rise 2.4 inches over the next century from just the melting that is occurring in Greenland. They also note that based on current numbers, it would take approximately 13,000 years for all of the ice in Greenland to melt.

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More information: Mapping Greenland's mass loss in space and time, Published online before print November 19, 2012, doi: 10.1073/pnas.1206785109 (PDF)

Abstract
The melting of polar ice sheets is a major contributor to global sea-level rise. Early estimates of the mass lost from the Greenland ice cap, based on satellite gravity data collected by the Gravity Recovery and Climate Experiment, have widely varied. Although the continentally and decadally averaged estimated trends have now more or less converged, to this date, there has been little clarity on the detailed spatial distribution of Greenland's mass loss and how the geographical pattern has varied on relatively shorter time scales. Here, we present a spatially and temporally resolved estimation of the ice mass change over Greenland between April of 2002 and August of 2011. Although the total mass loss trend has remained linear, actively changing areas of mass loss were concentrated on the southeastern and northwestern coasts, with ice mass in the center of Greenland steadily increasing over the decade.

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User comments : 5

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Moebius
1.5 / 5 (8) Nov 20, 2012
It will take 13,000 years for all of the ice in Greenland to melt which is the only way it can raise the sea level. Unless the ice slips off which will raise the level instantly.
VendicarD
5 / 5 (9) Nov 20, 2012
The 13,000 year figure presumes no change in the melt rate.

Yet the article claims an increase of 4.5 percent per year

Assuming a constant increase for the next 100 years, then the melt rate would be 5.50 times it's current melt rate. At that rate the entire Greenland ice cap would be gone in 2,000 years.

Sea level rise will also be similarly expanded.

If we assume continued proportional growth, then 4.5% per year causes an increase of 81 times. At that speed the Greenland ice cap will vanish in 160 years.

Lurker2358
5 / 5 (3) Nov 20, 2012
They also note that based on current numbers, it would take approximately 13,000 years for all of the ice in Greenland to melt.


Wrong professor. Even their own data doesn't say that.

2,850,000km^3 = 9km^3 * N*(N 1)/2

N ~ 796 years.

Isn't this like fifth grade level math?! The Sum of the first "N" terms, multiplied by a constant, in this case the rate of acceleration.

But this assumes there are no other variables involved accelerating the melt, but we know there are.

The real rate of melting is much faster than this.

Just pointing out the obvious fact that they don't even understand the most obvious consequences of their own data, and they're supposed to be the experts.
Lurker2358
5 / 5 (3) Nov 20, 2012
The 13,000 year figure presumes no change in the melt rate.

Yet the article claims an increase of 4.5 percent per year

Assuming a constant increase for the next 100 years, then the melt rate would be 5.50 times it's current melt rate. At that rate the entire Greenland ice cap would be gone in 2,000 years.

Sea level rise will also be similarly expanded.

If we assume continued proportional growth, then 4.5% per year causes an increase of 81 times. At that speed the Greenland ice cap will vanish in 160 years.


The albedo feedback is limited by maximum melt down and the curvature of the Earth, so that part of the feedback mechanism can't keep growing exponentially forever.

However, I think it's a very long way from reaching the maximum, seeing as how the sea ice is not even fully melted yet, and doubles again by the end of Octorber currently, and snow fall on land restarts almost as soon as the melt season is over.

The warm-up can accelerate quite a lot, but not forever..
VendicarD
5 / 5 (5) Nov 20, 2012
The question is, what amount of non-linearity can be expected?

Experts know that as the ice pack that traditionally is pushed to the northern shore of Greenland in the summer melts and as the surface waters warm, the Greenland melt rate will increase dramatically.

"Just pointing out the obvious fact that they don't even understand the most obvious consequences of their own data, and they're supposed to be the experts." - Lurker

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