Dr. Jeff Masters' WunderBlog

Antarctica melting?

Posted by: Dr. Jeff Masters, 6:44 PM GMT on March 07, 2006

Melting ice in Antarctica produced global sea level rises of 0.4 mm/year between 2002 and 2005, according to a new study published March 2, 2006 in the on-line journal Science Express. The study, titled "Measurements of Time-Variable Gravity Show Mass Loss in Antarctica", by University of Colorado researchers Isabella Velicogna and John Wahr, used satellite data from two NASA satellites called the Gravity Recovery and Climate Experiment (GRACE). The satellites measured the changing pull of gravity from the two large ice sheets covering Antarctica to determine how much ice was on the continent, and how fast the ice was changing. Most of the melting discovered was from the West Antarctic Ice Sheet. This is the smaller of the two ice sheets covering Antarctica, and holds enough ice to raise global sea levels 20 feet should it completely melt. The rock on which the West Antarctic ice rests is below sea level, and the sheet could be melting on its underside due to warming ocean waters penetrating there and melting it from both below and along the edges. The study found little melting of the huge East Antarctic Ice Sheet (which would raise global sea levels 200 feet if it were to melt). This ice sheet is on rock high above sea level, so warmer ocean waters cannot affect it. Additionally, the East Antarctic Ice Sheet has average temperatures so cold that even a 5-10C increase in temperatures is not expected to seriously threaten it.

The net Antarctic melting reported comes as a surprise, since the "official" prediction from the latest 2001 report from the Intergovernmental Panel on Climate Change is that global warming should cause increased precipitation over Antarctica this century. This increased precipitation is expected to exceed Antarctica's melting enough to decrease global sea level. This decrease in sea level by 2100 is predicted to be about 3 inches (8 cm), � 4 inches (10 cm), but would be offset by increases in sea level due to thermal expansion of the seas due to warmer water temperatures, plus melting of Greenland and glaciers on other continents.

As I reported in my blog on Greenland's greenhouse, total global sea level rise in recent years has been between 1.5 and 2.9 mm/year. Thus, the .4 mm/year contribution from Antarctica found by the new study represents a significant portion of this rise. However, another study published in December 2005 in the Journal of Glaciology titled, "Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992-2002" found a rate of melting for Antarctica five times smaller, for the earlier period 1992-2002. This research, performed by a team led by NASA scientist H. Jay Zwally, used satellite radar altimetry data from the European Remote-sensing Satellites ERS-1 and -2, and found a net melting of only .08 mm/year from Antarctica. Did Antarctica's melting really increase 5-fold in past three years? If so, is this a short term fluctuation, or indication of a long term trend? I'm of the opinion that's it's too soon to tell. It is extremely difficult to do mass balance studies of these huge ice sheets, since it requires finding a small change in a very large number. The same problem affects the recent estimates of Greenland's mass balance. The new study from the Journal of Glaciology also reported that between 1992 and 2002, the total mass of the Greenland Ice Sheet increased and thus Greenland caused a .03 mm/year decrease in sea level. This result is in contradiction to the two studies I quoted in my Greenland blog, by Box et al. (2004), who found that Greenland contributed to a net increase in global sea level of 1.5 mm/year, and Rignot et al. (2006), who found a .23 mm/year rise for the year 1996, increasing to .57 mm/year by 2005. I'd like to see at least three to five more years of satellite measurements before concluding that Antarctica or Greenland are undergoing significant melting. The European Space Agency is launching a satellite called CryoSat in March 2009 that should help answer these questions. If you want a more technical discussion of the issues, realclimate.org published a nice analysis last week.

Coverage in the press
It was interesting to watch the reaction of the press to the release of the new study. The New York Times titled their article, "Loss of Antarctic Ice Increases", and did a reasonable job covering some of the uncertainties. The USA Today was a bit more alarmist, headlining their article, "Study: Antarctic ice sheet in 'significant decline'". The Washington Post had a very alarmist title to their article, "Antarctic Ice Sheet Is Melting Rapidly". The facts and uncertainties involved in the making ice sheet balance measurements do not support this claim, as of now. Although any news of an increase in melting from Antarctica or Greenland is worthy of concern, I thought that in general, the media's headlines on the matter were too alarmist, given the uncertainties involved.

My next blog will be Thursday, when perhaps I'll be able to talk about Phoenix's first rain in 142 days. They've got a 20% chance of rain on Wednesday!

Jeff Masters

References
Box, J.E., D.H. Bromwich, and L-S Bai, 2004. Greenland ice sheet surface mass balance 1991-2000: Application of Polar MM5 mesoscale model and in situ data. J. Geophys. Res., 109, D16105, doi:10.1029/2003JD004451.

Rignot, E., and P. Kanagaratnam, "Changes in the Velocity Structure of the Greenland Ice Sheet" Science 311, 986-990, 17 February 2006, DOI: 10.1126/science.1121381

Is E.T coming? (Due)

This is a photo of myself during an Aurora Polaris. See the Alberto's comments for more information.

Antartica (darryl2)

Categories: Climate Change

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53. ForecasterColby 3:49 AM GMT on March 09, 2006
Water in contact with land does not cause friction, because land and water are not moving relative to one another. Inyo, not all science tends liberal - but as a group, intellectuals (which scientists are definetly among) tend liberal, both in all the polls and studies I've seen and in my own experience.

54. Skyepony (Mod) 3:59 AM GMT on March 09, 2006
As far as the glaciers melting causing the earth to gain mass at the equator, your right on ~ it's refered to as pumpkin earth. Different thing affect the speed though, that bad tsunomi sped it up ever so slightly. Member Since: August 10, 2005 Posts: 144 Comments: 29359

55. Inyo 8:47 AM GMT on March 09, 2006
I agree that a lot of intellectuals tend liberal, one take might be that they are being 'indoctrined' but another take could be that smarter people just tend to be liberal :) but on a more serious note, no, there is no way that melting glaciers are going to significantly affect the earth's movements relative to the sun or other planets. Keep in mind that huge ice sheets have covered the earth and melted back to nothing literally hundreds if not thousands of time in the earth's history. The earth didn't flip over, fly into the sun, or careen off into deep space any of those 100 times, why would it do it now? There are tiny effects, i remember reading somewhere that all the dams on earth have changed the earth's rotation VERY slightly by moving mass around. however, i think most scientists agree that the effects of this are completely insignificant compared to volcanos, comets, solar fluxuations, natural variations in the earth's tilt, and levels of co2 in the atmosphere. the earth is naturally slowing down in rotation, i think in the earth's history the day's length has increased by a couple of hours. However, the sun will go nova and incinerate the earth far before the effects of the rotation slowing would make a difference. Also, since no orbit is truly stable, the moon will eventually either fall onto the earth or careen off into space. However, again, this will be long after the sun is gone and the earth is a cold, empty rock. Member Since: September 3, 2002 Posts: 42 Comments: 765

58. Cregnebaa 1:34 PM GMT on March 09, 2006
Cyclone it's all relative terms, an ice skater with their arms out has a diameter of say 6feet arms in 2feet, hense the large change in spin. I don't think the ice melting will add another 16,000 miles of extra diameter. Pony was agreeing it would affect the spin speed but only by a tiny amount Member Since: October 19, 2005 Posts: 6 Comments: 322

63. HurricaneMyles 4:28 PM GMT on March 09, 2006
You're right in most aspect Inyo. The melting of ice is going to have a neglibible effect on the Earth. It's happened before, it will happen again, and without any consequences on the orbit or rotation of the Earth. I haven't heard about the dams having an effect on the Earth, but it would make sense. Just like the Indian Ocean Tsunami increased the day length by like 1/4 second or even less. Also the Earth has slowed down by a factor of 6. The Earth originaly spun so fast that a day took about 4 hours according to a study I once read. Due to the pull of the moon and the sun, we have slowed down to 24 hours in a day in the last 4 billion years. I dont remember how much we're slowing down now, but we aren't slowing very fast. A slower Earth isn't really a bad thing, anyways. If we adjusted the calander for it we'd be gaining time during the day, while having less days in a year, doesnt sound too bad to me. This will take millions of years though, so dont expect a calander change in our lifetimes. Member Since: January 12, 2006 Posts: 5 Comments: 827

64. jeffB 5:24 PM GMT on March 09, 2006
I haven't heard about the dams having an effect on the Earth, but it would make sense. Just like the Indian Ocean Tsunami increased the day length by like 1/4 second or even less. A lot less -- 2.68 microseconds, not 250,000. :-) Member Since: July 8, 2005 Posts: 0 Comments: 40

65. jeffB 5:27 PM GMT on March 09, 2006
As far as polar ice mass being redistributed toward the equator, yes, there would be a measurable effect, but only because we're really good at measuring really small changes. I'm not up to doing a back-of-the-envelope calculation, but I think we're talking far less than a millisecond even if ALL the polar ice melts. Member Since: July 8, 2005 Posts: 0 Comments: 40

66. Inyo 7:14 PM GMT on March 09, 2006
wow, four hour days, that must have been nuts. I wonder if convection was decreased due to less time in the sun, or if it just went all night. I guess back then the atmosphere wasnt in any way similar back then so who knows. as for cyclonebuster, if i had any respect for your knowledge of physics or science in the past, it is gone now. If the tunnels are as well thought out as your 'theories' on the earth flipping over, they are a lost cause for sure. Member Since: September 3, 2002 Posts: 42 Comments: 765

67. Lermanetdotcom 12:40 PM GMT on January 08, 2007
I would appreciate a 2nd opinion on the imagery that I have collected here: http://www.lermanet.com/antarcticmelt/ There appears to be substantial volcanism occurring along the transantarctic mountains near ross island. Email to alerma@verizon.net thanks arnie lerma

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