West Antarctic ice sheet may not be losing ice as fast as once thought – GRACE readings overestimated

From University of Texas, Austin via Eurekalert

New ground measurements made by the West Antarctic GPS Network (WAGN) project, composed of researchers from The University of Texas at Austin, The Ohio State University, and The University of Memphis, suggest the rate of ice loss of the West Antarctic ice sheet has been slightly overestimated.

WAGN sites in antarctica

WAGN sites in antarctica

“Our work suggests that while West Antarctica is still losing significant amounts of ice, the loss appears to be slightly slower than some recent estimates,” said Ian Dalziel, lead principal investigator for WAGN. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”

In 2006, another team of researchers used data from the Gravity Recovery and Climate Experiment (GRACE) satellites to infer a significant loss of ice mass over West Antarctica from 2002 to 2005. The GRACE satellites do not measure changes in ice loss directly but measure changes in gravity, which can be caused both by ice loss and vertical uplift of the bedrock underlying the ice.

Now, for the first time, researchers have directly measured the vertical motion of the bedrock at sites across West Antarctica using the Global Positioning System (GPS). The results should lead to more accurate estimates of ice mass loss.

Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum. Starting about 20,000 years ago, the ice began slowly thinning and retreating. As the ice mass decreases, the bedrock immediately below the ice rises, an uplift known as postglacial rebound.

Postglacial rebound causes an increase in the gravitational attraction measured by the GRACE satellites and could explain their inferred measurements of recent, rapid ice loss in West Antarctica. The new GPS measurements show West Antarctica is rebounding more slowly than once thought. This means that the correction to the gravity signal from the rock contribution has been overestimated and the rate of ice loss is slower than previously interpreted.

WAGN GPS deployed

“The published results are very important because they provide precise, ground-truth GPS observations of the actual rebound of the continent due to the loss of ice mass detected by the GRACE satellite gravity measurements over West Antarctica” said Vladimir Papitashvili, acting director for the Antarctic Earth Sciences Program at the National Science Foundation, which supported the research.

WAGN researchers do not yet know how large the overestimation was. A more definitive correction will be conducted by other researchers who specialize in interpreting GRACE data. Previous estimates of postglacial rebound were made with theoretical models. Assimilation of the direct GPS results into new models will therefore produce significant improvements in estimations of ice mass loss.

The results will appear in “Geodetic Measurements of Vertical Crustal Velocity in West Antarctica and the Implications for Ice Mass Balance” (M. Bevis et al., 2009), published in the electronic journal Geochemistry, Geophysics, Geosystems of the American Geophysical Union and the American Geochemical Society. [View the paper at: http://www.agu.org/journals/gc/gc0910/2009GC002642/ ]

A team from The University of Texas at Austin’s Jackson School of Geosciences (Ian Dalziel, lead principal investigator), The Ohio State University’s School of Earth Sciences (Michael Bevis), and The University of Memphis’ Center for Earthquake Research and Information (Robert Smalley, Jr.) performed the WAGN project.

The network consists of 18 GPS stations installed on bedrock outcrops across West Antarctica. Precise, millimeter level, three-dimensional locations of the stations, which are bolted into the bedrock, were determined during measurements made from 2001 to 2003 and from 2004 to 2006, the two measurements being at least three years apart. The difference in the positions during the two time periods indicates the motion of the bedrock.

The WAGN data were supplemented with data from the first year of the Polar Earth Observing Network (POLENET) project, a project to establish a more sophisticated, continuously recording network of GPS and seismic stations, including the already established WAGN sites. POLENET will further improve our understanding of the interaction between the solid earth and ice sheets at both poles. The lead principal investigator of the U.S. Antarctic contribution to POLENET is Terry Wilson of The Ohio State University.

###

The West Antarctic GPS Network and the U.S. Antarctic contribution to the Polar Earth Observing Network of the International Polar Year were both funded and logistically supported by the Office of Polar Programs of the National Science Foundation.

About these ads

84 thoughts on “West Antarctic ice sheet may not be losing ice as fast as once thought – GRACE readings overestimated

  1. There are a couple of interesting points. They say the west antarctic is not melting as fast as thought, but then add that there is a net loss of ice from the antarctic. I was under the impression that the antarctic is a net gainer of ice.

    They also say that previous estimates of post glacial rebound came from models. It is at least refreshing that a long last science is being done with real data. Who knows, it might catch on!

  2. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”

    Isn’t there wayyyyy more new ice in the rest of Antarctica being made, easily dwarfing the small amount list in West Antarctica?

  3. Starting about 20,000 years ago, the ice began slowly thinning and retreating.

    Pesky cavemen and their darn SUV’s. These people need to be held responsible, for creating the horrible world we live in today. Morally they should be willing to sign a treaty that gives us all of their treasure, and everything else they hold dear as a start to paying us back for all the harm they have done.

    Then perhaps they could fall on their stone spears so that their presence would not continue to pollute the planet. Of course an environmentally friendly method of disposing of their remains needs to be found. Justice requires that they let us tax them to fund this research.

    However we find that the cavemen leadership who embrace hope and change and all things utopian need to be revered above all. At least until we, the peaceful protectors of the planet are strong enough to overcome the evil/revered cavemen, and then under the bus they go…

  4. What about a simpler global measure. If there is more ice at the poles, it would seem the length of day would decrease and less ice at the poles, the length of day would increase. When I first started looking at AGW I ran across this several times but have not lately. It seems so simple. Am I missing something about distribution of mass around the globe?

  5. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.” The article is reviewing an error in West Antarctica data, how did that become Antarctica?

  6. One might think that a huge ice sheet as in Antarctica doesn’t respond much to shorter climatical change, such as a century of warning. Is it possible that the current ice loss still is a response to the end of the last ice age?

  7. The network consists of 18 GPS stations installed on bedrock outcrops across West Antarctica. Precise, millimeter level, three-dimensional locations of the stations

    Since when has GPS been able to measure anything down the the millimeter level? I have no doubt there is a post glacial rebound…I just question the accuracy of the measurements.

  8. References please, is the Antarctic currently having anet gain or net loss of ice? If a net loss is this a continuation of the interglacial loss or something new and larger?

  9. WAGN ? I think I would avoid accronyms with WAG in them. Although there are a number of networks like the GHCN in which WAG would be an appropriate one.

  10. Brilliant. And here we have additional evidence that all is well and everything is to do with natural cycles. The evidence now emerging juxtaposed with the so- called consensus is becoming more and more compelling.
    There is much more balanced science coming forward (from limited “accepted” sources) as the researchers feel less threatened and/or grow really large cajones.
    It is not always/never easy to be in contention with the current political meme. (Theorists point out that memes which replicate the most effectively spread best, and some memes may replicate effectively even when they prove detrimental to the welfare of their hosts.)
    Sort of sums it up for me.

  11. As an addendum to that last post I must add that we really don’t have a monkeys about what is actually happening. But catastrophic warming it ain’t so far.

  12. Sean (10:07:54) : NO!!! If we look at all of the ice at once the warming signal would be lost. It only makes sense to focus on the areas where the ice is melting. This is what proves that the planet is warming. That way we can prove to the sheeple that disaster is immi.. ah emme… darn im… ahhhhh… that disaster is on the way and we can save them by destroying them. It’s so simple…

  13. Since when has GPS been able to measure anything down the the millimeter level?

    Carrier phase tracking yields accuracy to a few mm. The receivers that are capable of doing this are rather expensive (a $10K receiver is capable of a few cm accuracy, according to a colleague of mine), and probably only maintain that level of accuracy if whatever they are sitting on moves very, very slowly, e.g., plate tectonics.

    The first time someone mentioned this (recently), I was similarly surprised so I did a little research and discovered it was indeed possible. Now I work for a GPS company, coincidentally enough, and will be required to really dig deep into the concepts used in navigation.

    Mark

  14. If the ice in Antarctic and Arctic is in the water, (icebergs etc) if 7/8th is under water to start with – when it melts it wont make much difference to the water levels – will it? Would have thought that ice on land melting will be the problem with water levels?
    Oh anyway people making statistics can make them say anything they want, they just baffle everyone with science to frighten us all. And frightened people obey orders. Too many politicians screaming about global warming, not enough scientists proving them wrong.

  15. This means that the correction to the gravity signal from the rock contribution has been overestimated and the rate of ice loss is slower than previously interpreted.
    So, it’s global warming, let’s get our tickets to copenhagen!

  16. Robert M. (10:07:40) :

    Starting about 20,000 years ago, the ice began slowly thinning and retreating.

    Pesky cavemen …

    I hear they all work for GEICO now.

  17. Sean (10:07:54) : What about a simpler global measure. If there is more ice at the poles, it would seem the length of day would decrease and less ice at the poles, the length of day would increase. When I first started looking at AGW I ran across this several times but have not lately. It seems so simple. Am I missing something about distribution of mass around the globe?

    IIRC “Spin Orbit Coupling” causes the orbital mechanics of the earth to also cause subtile shifts in LOD. There was a paper (by an English speaker who I think is an Aussy, but to be published in Russian, since they have Scientists who actually read and do Science…) that linked LOD changes with PDO changes. Wilson? Time to go digging…

    Ah, found it. We were talking about this kind of stuff here:

    http://chiefio.wordpress.com/2009/03/09/are-we-quaking/

    And in comments the paper was discussed with a link to a slide show version of what was to be in it here:

    http://www.lavoisier.com.au/articles/greenhouse-science/solar-cycles/IanwilsonForum2008.pdf

    Don’t know the eventual publishing fait, but I presume the ‘cute bits’ like the fuzzy baby chicken got removed…

    h/t to Geoff Sharp at http://landscheidt.auditblogs.com/ for his original pointer to the article in those comments.

    So while it might be an interesting proxy for ice, it might be for reasons beyond most ken, and, well, proxies can be tricky things to domesticate…

  18. As I understand it the UK and much of Europe is still undergoing rebound from the melting of ice from the last ice-age 10,000 years ago. I would imagine that something similar is happening in Antarctica and it would say nothing about current temperature or melting.

    And of course rebound is not the only thing to change land surface levels. Seismic activity and Volcanicism with underground/underice magma movement must be happening in places given that Antarctica has its share of volcanoes.

    But surely the loss or gain of ice from Antarctica is simply the balance betwen melting and precipitation. More precipitation means more ice to melt. Less precipitation means less. Current rates of ice melt at the edges might say more about what the weather was like a few centuries ago than anything more recent.

    I see mention of ‘contributing to rising sea levels’. What rising sea levels? I see no evidence of it and I live in a coastal town. As I have posted before any rising or falling sea level surely has to relate to the total balance of water into the ocean. And a lot of rivers are now discharging a lot less water into the ocean because of human use. Somewhat more (if it is really happening) from the ice rivers around the planet might just be making up for (some of?) the loss.

  19. Liz (10:51:34) : If the ice in Antarctic and Arctic is in the water, (icebergs etc) if 7/8th is under water to start with – when it melts it wont make much difference to the water levels – will it? Would have thought that ice on land melting will be the problem with water levels?

    Exactly. Floating ice does not change the water level when it melts. Easy home experiment. Fill glass with ice. Add water to the brim (some ice will be above edge). Wait. As Ice melts, the water level stays constant.

    For advanced study, fill glass with ice, fill to brim with gin. When the ice melts the level will be very slightly different. (Water and alcohol are different densities and the liquids merge a bit on melting). Then drink dilute gin. Repeat until you get the expermimimint chow prowdush za deesireed reshultsh.

    Oh anyway people making statistics can make them say anything they want, they just baffle everyone with science to frighten us all.

    This is just wrong. Only 79% of statisticians can abuse statistics in that way to a 95% confidence interval, the other 21% are still grad students or have a “morals problem” ;-)

  20. If the land is going up in Antarctica and in places like Greenland and Scotland, doesn’t that imply that the land has to “come from somewhere”? And if it comes from somewhere, doesn’t that somewhere have to go “down”? And isn’t a lot of the planet surface ocean bottom? So wouldn’t some of that “going down” be ocean bottom? If so, then the ocean would drop a bit, not rise…

    So I’d expect all that melting (if any) to be partly offset by a deeper bucket to put it into. Sizes? Sadly, this is still at the “speculative qualitative phase”, but if anyone has pointers to anything more quantitative…

  21. Yes, exaclty. What rising sea levels?
    Where are the before & after pics?
    We have produced the pictures of the Submarines at the North Pole in 1959 and on.
    Where are AGW’s pictures of rising sea levels?
    There aren’t any. Because the sea levels are NOT rising.
    I have picture of a Ca. coastal city showing rock formations and the sea level, taken 60 years apart. You cannot tell the difference.
    Whatever melting has taken place in the last 60 years, it’s trivial.

    Let’s do a topic on Sea Levels. Won’t that be fun.

  22. Skeptic Tank (11:10:03) :

    Nope! There are GEICO rejects that work for the US government and the ones that couldn’t get on there, work at the UN.

    Liz (10:51:34) :
    “If the ice in Antarctic and Arctic is in the water, (icebergs etc) if 7/8th is under water to start with…”

    Antarctic ice is mostly on the continent of – Antarctica. That is what that brownish stuff in the picture is. No brownish stuff in the Arctic, so yes the ice there is floating…

  23. Three points:

    1. As several posters have noted, this research says NOTHING about the Eastern Antarctic Ice Sheet, where ice is increasing.

    2. Post-Glacial Rebound is a process that takes THOUSANDS OF YEARS. The rise we’re seeing today is related less to any CURRENT temperature changes than to temperature changes 10,000 years ago (that’s right, the end of the last glacial period).

    3. When confronted with the FACT that ice in Antarctica, as a whole, is on the increase, global warming alarmists fall back on what seems like a counterintuitive explanation of how warmer weather, can in fact, result in more ice. You see, warmer weather means more evaporation of ocean water, which in turn means more precipitation. Precipitation, at least over Antartica, will ALWAYS be in the form of snow (unless the planet warms a hell of a lot more than even the worst alarmists predict). More snow means more ice on the continent. And so, though it seems perverse, warmer weather is perfectly consistent with more ice on Antarctica.

    The problem is, if you accept this explanation (and I do), then if Antarctica were truly melting, then it can only be because the planet is getting COOLER.

    You can’t have it both ways, alarmists. Either warming causes an increase in ice, or it causees a decrease. But you guys have a long history of taking whatever WEATHER happens to be occuring, anywhere on the planet, and blaming it on global warming. If temperatures increase, it’s global warming. If temperatures decrease, it’s global warming. If ice increases, it’s global warming. If ice decreases, it’s global warming. If sea levels rise, it’s global warming. Is sea levels fall, it’s global warmng. If hurricanes increase, it’s global warming. If hurricanes decrease, it’s global warming. If the upper atmosphere warms more than the surface, it’s global warming. If the surface warms more than the upper atmosphere, it’s global warming. If species die, it’s global warming. If species thrive, it’s global warming.

    So I have a question for all of you alarmists out there. What, exactly, would you accept as evidence that global warming is not occurring? Is there anything at all?

    Of course, many of you alarmists might ask the opposite question of us skeptics – what would WE accept as evidence that global warming IS occurring? And I will be glad to answer that question. If we had a worldwide, geographically representative, reliably monitored, scrupulously maintained, and UNBIASED temperature record of 100 years or longer, with no “adjustments” made by “scientists” who have a dog in the fight, and that record showed that the “global average temperature” had increased by more than half a degree Celcius over those 100 years, I would accept that as evidence of global warming.

    It still wouldn’t prove that the temperature increase is “unusual”, or “unprecedented”, let alone that it was “anthropogenic”. But at least you would have me convinced that temperatures are rising.

    Regards,
    Trevor

  24. EN Smith, cheers, tried the gin recipe – superb. Going to try other spirits for the next few evenings, do you think it will work with Rum and coke and ice? lol

  25. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”

    Translation: “Please, Mr. Gore, don’t call our bosses and demand that we be replaced with hard-core warmists.

  26. rbateman (12:16:20) :

    Does it look like sea level rise is more rapid during cooler times? Or am I still blind in one eye and unable to see out of the other.

  27. I was just wondering how these guys can reconcile the “current” ice loss in Antarctica with the “current” 30 year cooling trend on that continent? Particularly when AGW theory states that Antarctica will actually gain ice due to increased precipitation….

  28. The earlier GRACE results were published in Velicogna & Wahr (2006)…

    Measurements of Time-Variable Gravity Show Mass Loss in Antarctica
    Isabella Velicogna1,2* and John Wahr1*

    Using measurements of time-variable gravity from the Gravity Recovery and Climate Experiment satellites, we determined mass variations of the Antarctic ice sheet during 2002–2005. We found that the mass of the ice sheet decreased significantly, at a rate of 152 ± 80 cubic kilometers of ice per year, which is equivalent to 0.4 ± 0.2 millimeters of global sea-level rise per year. Most of this mass loss came from the West Antarctic Ice Sheet.

    1 University of Colorado, Cooperative Institute for Research in Environmental Sciences and Department of Physics, University Campus Box 390, Boulder, CO 80309–0390, USA.

    2 Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 300-233, Pasadena, CA 91109–8099, USA.

    They found that the WAIC was losing ~148 km3 per year of ice mass and that the EAIS was stable from 2002-2005.

    This chart summarizes their results. This chart summarizes their results. The green series is the EAIS and the red is the WAIS.

    The total ice volume of Antarctica is about 20 to 25 million km3… 90% in the EAIS and 10% in the WAIS. A 148 km3/yr ice loss from the WAIS represents 0.007% per year. A 152 km3/yr ice loss from all of Antarctica represents 0.0008% per year.

    So, if the PGR was overestimated, the EAIS (90% of Antarctica) is gaining ice mass and the WAIS (10% of Antarctica) is losing less than 0.007% of its ice volume per year.

  29. Tom:

    2″ in 40 years. That’s .05″ / year.
    .05″ turns out to be the thickness of a dime.
    So, the sea level rise turns on a dime.
    So, in 8009, Sacramento, Ca. will be lapped by breakers.
    Projecting the NASA trendline, of course, 6000 years into the future.
    Not to worry, by then the IPCC will have grown from the Intergovernmental Panel to the Interplanetary Panel.

  30. “I have picture of a Ca. coastal city showing rock formations and the sea level, taken 60 years apart. You cannot tell the difference.
    Whatever melting has taken place in the last 60 years, it’s trivial.”

    Exactly, I live in coastal Nova Scotia, at the mouth of the Bay of Fundy. I regularly go for walks on the salt marshes that provided hay for the Acadians that settled this area 300 years ago. http://obpl.com/hy-mrsh.html or this one, http://museum.gov.ns.ca/arch/infos/infoaca2.htm

    You can still walk the dykes that they built farther up the Bay, http://www.acadian-home.org/IMAGES/Present-day-dike-Hortons-Landing.gif

    That green kool aid must taste really good, our province has been sucking it back for years.

    Your taxes at work, no time for reality, sigh.

  31. The Pineapple Upside Down Hockey Stick cake goes flat. In Search of-Mannian.
    So, everything that they say, invert it.
    Then apply the Flatfied correction.
    Global Cooling cancels Global Warming.
    Sea Levels are rising-dropping faster than anyone had previously forgotten they had imagined.
    The Arctic Sea Ice is melt-recovering faster than anyone had mis-predicted.
    Hurricanes in the Atlantic are forecast-disappearing faster than you can say bibbity-bobbity-boo.
    The coming Ice Age meets Global Warming at Copenhagen, and an immense burst of light takes place as doesn’tMatter meets neverMind.
    Enough power will be produced to run CERN for the next year, drop cord not included.

  32. re E.M.Smith (11:19:18) ‘… proxies can be tricky things to domesticate’
    Which is why one should only keep the tame ones.
    The ones that can be handled most easily.
    The ones that are most malleable.
    The ones that can be made do what you want them to do.

  33. The GRACE satellites do not measure changes in ice loss directly but measure changes in gravity, which can be caused both by ice loss and vertical uplift of the bedrock underlying the ice.

    Isn’t there an active volcano in Western Antarctica ? … that could be causing a vertical uplift of the bedrock ??

  34. rbateman (11:46:41) : Where are AGW’s pictures of rising sea levels? There aren’t any. Because the sea levels are NOT rising.

    I thought sea levels were still rising (steadily at same rate) as per CSIRO but then encountered David Stockwell’s sea level by altimeter showing fall since 2006 – but data still stops short of today – it could have turned direction again. As to TOPEX/Jason, draw a trend line for TOPEX and another for Jason, and the trend is definitely flattening.

    rbateman, as to your NASA pic, I don’t understand where that fits into all the above. Can you help? Does it stop at 2005 because of the evidence David Stockwell shows? Where should it be now?

    So what is “THE TRUTH”? heh?

  35. Sadly, oh, sadly, Paul Hudson (of recent fame for his good BBC article giving skeptics an inch) has returned to the fold and his recent piece does the correct genuflecting again and his first commenter says thank you for returning to the fold.

    However, I’d still like to hear other skeptics’ opinions on his comments:

    … Well, as odd as it may seem, global warming may well be responsible [for increased Antarctic sea-ice], according to Jinlun Zhang, an oceanographer at the University of Washington.

    He has pieced together a complex computer model that helps explain why Antarctic sea ice is growing even with signs that ocean and air temperatures are on the rise. The key is that warming temperatures can lead to more stratified ocean layers…

    [etc]

  36. There’s something bugging me about the concept of Post Glacial Rebound (PGR) in Antarctica…

    Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum. Starting about 20,000 years ago, the ice began slowly thinning and retreating. As the ice mass decreases, the bedrock immediately below the ice rises, an uplift known as post glacial rebound.

    If “Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum”… Why isn’t there a huge unconformity in the ice cores? There’s no section missing from the ice cores. At least not from the ice cores that have been used for temperature and CO2 reconstructions.

    If Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum,” several thousand years of ice deposition should be missing from the Votok and other ice cores starting in the Holocene… But there isn’t any missing section.

    I suppose that the Antarctic ice sheet extended farther north, since sea levels were lower during the Pleistocene… So, ice cores closer to the coast should have encountered unconformities… But it doesn’t seem likely to me that Antarctica should have experienced much in the way of PGR.

    There are also some publications that suggest that parts of the EAIS might have actually been thinner (or even ice-free) during the Last Glacial Maximum than it is now…

    Geology; December 2001; v. 29; no. 12; p. 1103-1106

    Bunger Hills, East Antarctica: Ice free at the Last Glacial Maximum

    D.B. Gore1, E.J. Rhodes2, P.C. Augustinus3, M.R. Leishman4, E.A. Colhoun5 and J. Rees-Jones6
    1 Department of Physical Geography, Macquarie University, Sydney, New South Wales 2109, Australia
    2 Research Laboratory for Archaeology and the History of Art, Oxford University, 6 Keble Road, Oxford OX1 3QJ, UK
    3 Departments of Geography and Geology, University of Auckland, Auckland 1030, New Zealand
    4 Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
    5 School of Geosciences, University of Newcastle, New South Wales 2308, Australia
    6 Oxford Authentification Ltd., Boston House, Grove Technology Park, Wantage, Oxfordshire OX12 9FF, UK

    Optically stimulated luminescence dating of glaciofluvial and glacial-lake shoreline sediments indicates that the Bunger Hills area, in coastal East Antarctica, was largely ice free by the Last Glacial Maximum (LGM). Deglaciation commenced as early as 30 ka, and the southern hills were completely exposed by 20 ka. The sediments do not record evidence of an LGM readvance. Previous reconstructions of LGM ice limits for the area are incompatible with this new evidence.

    Quaternary Science Reviews
    Volume 21, Issues 1-3, January 2002, Pages 203-231
    Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles

    Philippe HuybrechtsCorresponding Author Contact Information, E-mail The Corresponding Author

    Alfred-Wegener-Institut für Polar-und Meeresforschung, Postfach 120161, D-27515 Bremerhaven, Germany

    Abstract
    New experiments were performed with three-dimensional thermomechanical models of the Greenland and Antarctic ice sheets to simulate their behaviour during the glacial cycles, to reconstruct their thickness and extent at the Last Glacial Maximum (LGM), and to estimate their glacio-eustatic contribution to the global sea-level stand. The calculations used improved ice-dynamic and isostatic treatments, updated datasets on higher grid resolutions, and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations. Results are discussed from a reference run with standard parameters that is compared with available glacial-geological observations, and from a series of sensitivity experiments focusing on isostatic adjustment, thermomechanical coupling, climatic forcing, mass-balance changes, and basal melting rates and viscosity changes of Antarctic ice shelves. For the Antarctic ice sheet, we find that volume changes are closely linked with grounding line changes of the West Antarctic ice sheet. At the LGM, the grounding line extended close to the continental shelf break almost everywhere. Ice over central East Antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations. For the Greenland ice sheet, melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the Eemian. At the LGM, the Greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas. For a plausible range of parameters, the experiments indicate that at the time of maximum sea-level depression (21 kyr BP), the Antarctic ice sheet contributed 14–18 m to the sea-level lowering, and the Greenland ice sheet 2–3 m, significantly less than the older CLIMAP reconstructions. Whereas both ice sheets were at 21 kyr BP close to their maximum extent, the experiments also indicate that their maximum volumes were reached only by 16.5 kyr BP (Greenland) and 10 kyr BP (Antarctica), equal to an additional sea-level lowering of, respectively, 0.4 and 3.7 m. Holocene retreat was essentially complete by 5 kyr BP in Greenland, but is found to still continue today in West Antarctica before reversing to growth during the next millenium. The models were found to reproduce gross features of the ice sheet’s history since the LGM in reasonably good agreement with available glacial-geological data, although observational control on ice thickness changes remains very limited.

  37. “E.M.Smith (11:42:41) :

    If the land is going up in Antarctica and in places like Greenland and Scotland, doesn’t that imply that the land has to “come from somewhere”? And if it comes from somewhere, doesn’t that somewhere have to go “down”?”

    You are quite right. When an icecap weighs down the crust the displaced material flows outwards and forms a “forebulge” around the icecap. When the ice melts the material slowly flows back. The “hole” where the ice was fills in and the bulge around it subsides. This is the reason Scotland and Scandinavia is rising while southern England, Netherlands, Northern Germany and most of Denmark is sinking. It’s the same in North America, most of Canada is rising while the southeastern US is sinking. You can easily see this on a map, a sinking coast typically has “rias”, drowned river valleys. There are any number of these from New Jersey southward. The maximum sinking rate is near the Chesapeake, as one might guess and then decreases southward to zero somewhere in the Caribbean.

  38. NSIDC shows increasing total Antarctic sea ice for the past 30 years:

    Some months show much higher rates of increase. Global total sea ice is also increasing (I’ve lost the link if anyone has it ?).

  39. How exactly do the “grace satelites work. I mean they appparently use models to determine what they actualy measure. Models mean “guess”. We guess how much the tides affect each and every measurement grace makes, we guess how orbital changes effect each and every measurement, we guess how much tidal effects on land effect measurements of gravity, we guess how much density changes in the mantle effect gravitational measurements, This could go on, and on , and on.

    Educated guess, well sure, but we know scientist are not immune to political results based on current and future funding.

  40. EM Smith, ocean basins rising or sinking, I do not know. We have only had 10,000 years or so of rapidly rising sea level, which would tend to, over how long?, reverse any rebound from low sea levels. How much earth is deposited into oceans via rivers? How much water enters the atmosphere from space? ???? so many?, so much to learn

    I am easily irratated by those who KNOW, and want to determine costly public policy.

    Cheers

  41. “Liz (12:02:42) :

    EN Smith, cheers, tried the gin recipe – superb. Going to try other spirits for the next few evenings, do you think it will work with Rum and coke and ice? lol”

    Don’t try it with tequila…I still haven’t found my pants.

    JimB

  42. “Trevor:
    “…You can’t have it both ways, alarmists. Either warming causes an increase in ice, or it causees a decrease. But you guys have a long history of taking whatever WEATHER happens to be occuring, anywhere on the planet, and blaming it on global warming. If temperatures increase, it’s global warming. If temperatures decrease, it’s global warming. If ice increases, it’s global warming. If ice decreases, it’s global warming. If sea levels rise, it’s global warming. Is sea levels fall, it’s global warmng. If hurricanes increase, it’s global warming. If hurricanes decrease, it’s global warming. If the upper atmosphere warms more than the surface, it’s global warming. If the surface warms more than the upper atmosphere, it’s global warming. If species die, it’s global warming. If species thrive, it’s global warming.”

    Well said. I’ve sent your post to a few of my “alarmist friends”, as it does a great job of summing up their typical responses anytime we enter a discussion about this.

    JimB

  43. Lucy Skywalker (13:32:05) :

    The melting should relate to the sea levels/warming.
    I really cannot tell you why NASA has no graph beyond 2005 on that site.
    Perhaps it’s the rate of rise/melting/warming is not as significant as predicted by some.
    Which relates back to West Antarctic Sheet melting/ice loss. The rates of increase are immersed in the noise of land-mass movements and expansion-contraction of warming/cooling oceans.
    It’s a Signal to Noise Ratio thing, Lucy.
    The other thing about NASA is that Congress has not been exaclty kind to them regarding funding and demands they place on them.
    I had thought that after the Hubble thing and the public outcry to save it, that we had demonstrated to Congress that we value what they do.
    I would like to hear NASA’s side of it. Are they swimming in data they have not the funds to process? I wonder.

  44. I know that by doing diferential GPS measurements you can improve accuracy. But mm accuracy? realy? Also, GPS is not very accuriat for vertical measurements. it seems to be about 3times worse than horizontal measusements.

    I suppose these guys are smart, and compensated for all that, but seems a little odd.

  45. There is a substantial literature on glacial isostasy and its effects on local and global sea level and Earth Rotation.

    Search on names like WR Peltier, Kurt Lambeck and RI Walcott as examples. There are many more as well.

  46. rbateman (11:46:41) :

    Yes, exaclty. What rising sea levels?
    Where are the before & after pics?

    You obviously missed Anthony’s post Maldivians sink to new low with an underwater publicity stunt. Clear proof that sea levels have risen dramatically recently, probably more than Gore or Hansen could hope for. ;^)

  47. Skeptic Tank (11:10:03) :

    “Nope! There are GEICO rejects that work for the US government and the ones that couldn’t get on there, work at the UN.”

    Warming Alarmism. So easy a caveman can do it.

  48. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”

    Antarctic ice has been growing for 30 years. Global sea ice is now increasing. How could this be in any way contributing to sea level rise? Unless of course researchers with “take home messages” have discovered a fourth phase for the water molecule, new “AGW ice” with a higher specific gravity than liquid water.

    I can see a few other possible explanations for tiny uplift on the west Antarctic continent besides rebound as ice melts. Has there been a similar measurement on the east of the continent to detect the depression from 30 years of increasing ice? What about the underwater volcanoes recently found off west Antarctica? Any chance boring old tectonics may have a role?

  49. Jeff in Ctown (Canada) (14:11:57) :

    I know that by doing diferential GPS measurements you can improve accuracy. But mm accuracy? realy? Also, GPS is not very accuriat for vertical measurements. it seems to be about 3times worse than horizontal measusements.

    I suppose these guys are smart, and compensated for all that, but seems a little odd.

    We can only hope that GPS is that accurate even in the vertical measurement. I shudder every time I hear that “scientists” are making compensations for anything.

  50. Re: Robert M. (10:38:58) – lol – thanks for a good laugh

    Re: Sean (10:07:54) — good to see people are thinking about this

    Re: E.M.Smith (11:19:18) — I’m exploring it further:

    Vaughan, P.L. (2009). (DRAFT) Combined Oscillations of Terrestrial Polar Motion, Solar System Dynamics, & the Lunar Nodal Cycle.

    http://www.sfu.ca/~plv/DRAFT_VaughanPL2009CO_TPM_SSD_LNC.htm

    As you can see (if you have the time/patience to read through it line-for-line), I next have to incorporate info about nutation cycles.

    Related:
    Some around here might find this noteworthy:

    Vaughan, P.L. (2009). 11.1 Year Cycle in Solar System Dynamics.

    http://www.sfu.ca/~plv/VaughanPL2009_11.1aCycleSSD.htm

    (freshly updated – more updates forthcoming…)

  51. ******************
    Konrad (14:48:46) :
    I can see a few other possible explanations for tiny uplift on the west Antarctic continent besides rebound as ice melts. Has there been a similar measurement on the east of the continent to detect the depression from 30 years of increasing ice? What about the underwater volcanoes recently found off west Antarctica? Any chance boring old tectonics may have a role?
    ********************
    Glad I saw your post. I was thinking the same thing. Ground in various regions around the world rise and fall without any involvment from ice. Once again, we have a proxy that responds to more than one independent variable.

  52. I read somewhere that the high level of GPS accuracy comes from leaving the receiver/recorder system at a stable location, like the bare rock of a nunatak peak, and leaving it there for weeks to months. Every reception reduces the error by a small amount. Given enough measurements, mm. accuracy may be possible. Can our new hire at the GPS Co. put the question to the old hands at coffee break?

  53. Lucy Skywalker (13:40:36) “However, I’d still like to hear other skeptics’ opinions on his comments:

    “… Well, as odd as it may seem, global warming may well be responsible [for increased Antarctic sea-ice], according to Jinlun Zhang, an oceanographer at the University of Washington.

    He has pieced together a complex computer model that helps explain why Antarctic sea ice is growing even with signs that ocean and air temperatures are on the rise. The key is that warming temperatures can lead to more stratified ocean layers…”

    2 words:
    Barkin
    Sidorenkov

    (…btw I don’t consider myself a ‘skeptic’, but rather a ‘non-alarmist’.)

  54. John Nicklin (14:47:51) :

    Do you live in the Maldives? I don’t.
    But there a plenty of other low-lying Islands to examine.
    Los Angeles is known to be sinking, but you don’t hear of advancing tides taking out major portions of that city. At 1″ per century, coupled with 2″ in the last 40 years, the sea has risen with respect to LA a shocking 3″.
    Wow.
    LAX – Los Angeles International Airport 100′ elevation.
    The airport will be inundated at present sinking/sea rise in 16,000 years.

  55. Trevor (12:01:08) “You can’t have it both ways, alarmists. If [....], it’s global warming. If [....], it’s global warming. If [....], it’s global warming. [...]“

    Nice – almost ROTFL here, at the 2+2=5 “simplification”.


    Meanwhile, belief in truth & reality remains an option for some …

    Sidorenkov, N.S. (2003). Changes in the Antarctic ice sheet mass and the instability of the Earth’s rotation over the last 110 years. International Association of Geodesy Symposia 127, 339-346.

  56. East Antarctica is a craton ” A core of stable continental crust within a continent and composed wholly or largely of Precambrian rocks with complex structures.”,i.e. is relatively stable geologically, has 90% of the continents ice and growing. The geology of West A is vastly different,geologically active with mountain building with slopes that grow glaciers that tip into the sea (like the west coast of North America).
    So all of this ‘shock,horror’ about WA loosing ice is a bit precious,sure get the RATE of loss a bit more accurate but you cannot compare stable EA with mountainous WA and expect the same ice retention…….one continent two vastly different geologies.

  57. Please, can someone give me some advice. I am considering attending a meeting of my state’s “Legislature’s Public Utilities and Technology Interim Committee’s meeting this Wednesday in the a.m. Roy Spencer (Heartland Institute) and Jim Steenburgh (U of Utah) have been invited to give presentations. If I were to go, I’d like to take copies of the best article that would sway the opinions of this group of lawmakers that AGW is a fraud foisted upon the public and their pockets.

    Any suggestions? If so, please give a web link to the article. Again this meeting is Oct 21st in the morning. Thanks for your help.

  58. “JimB (13:59:53) :

    “Liz (12:02:42) :

    EN Smith, cheers, tried the gin recipe – superb. Going to try other spirits for the next few evenings, do you think it will work with Rum and coke and ice? lol”

    Don’t try it with tequila…I still haven’t found my pants.

    JimB”

    Me too, and I had a mytery NZ$300 EFTPOS debit that night as well. Oh, lsoing your pants and that myster debit was caused by global warming, or was it the other way around? Hummm….it was a rather large quantity of tequila, so I am told.

  59. Every scientist after spending hundreds of thousands of dollars needs to announce some exciting conclusions before he can ask for more money. This is another example. The end result is the ice is continuing to melt as it has for the last 20,000 years. Oh hum.

  60. Sioned L
    You might try this site (wattsupwiththat.com) and the references to the phoney “hockey stick” and the “loss” (or destruction?) by the British university group of the world wide temperature data supporting their claimed last 100 years of the earth’s temperature rise of 0.7C. Both are key arguments in the IPCC reports and are collapsing.

  61. Paul Vaughan (16:32:09) :

    Trevor (12:01:08) “You can’t have it both ways, alarmists. If [....], it’s global warming. If [....], it’s global warming. If [....], it’s global warming. [...]“

    Nice – almost ROTFL here, at the 2+2=5 “simplification”.

    But two plus two can equal five, for extremely large values of two.

    These days, of course, any value of ‘two’ that is ‘adjusted’ by Al Gore Warmists will almost certainly be ‘three’ anyway, or course. So it’s even worse than we thought – it’s six!

  62. Trevor:

    From the article linked to by Lucy above.

    Water-logged sea ice also may explain why sea ice in the Antarctic is increasing. This occurs when the weight of accumulated snow presses down on a slab of sea ice until it’s nearly submerged. When that happens, waves cause ocean water to spill on top of the ice and into the snow, forming a layer that eventually freezes and becomes “snow ice.”
    So, global warming is not only thought responsible for the melting of Arctic ice over the last few decades, but the observed increase in the ice at Antarctica, too.

    http://www.bbc.co.uk/blogs/paulhudson/2009/10/the-polar-ice-conundrum.shtml

  63. Paul Vaughan:

    “Nice – almost ROTFL here, at the 2+2=5 “simplification”.


    Meanwhile, belief in truth & reality remains an option for some …”

    Not sure I understand you here Paul. Are you saying that *I* am guilty of oversimplification, and not believing in truth and reality? Or that the alarmists are guilty of same?

  64. Wondering Aloud (10:26:13) :

    “WAGN ? I think I would avoid accronyms with WAG in them. Although there are a number of networks like the GHCN in which WAG would be an appropriate one.”

    I was thinking the same thing, regarding WAG Network. I mean, sheeze. I want to respect the science here, but…c’mon!

  65. Each year, the earth moves 15 centimeters, or 6 inches, further away from the Sun. Thus, assuming the distance by which the radius increases is constant, back in 1 BC, the earth was 1000′ closer to the Sun than it is today, or slightly less than a quarter of a mile (4 NYC blocks).

    If the distance between the earth and the Sun increased by 300,000 miles a millennium, as these global warming quacks claim in their article, then in 100,000 years, the earth would be 123,000,000 miles from the Sun, and temperatures would be slightly warmer than those encountered on Mars and we would have long since frozen to death, even if everyone helped prevent global freezing by driving a Hummer.

  66. May not the scientists and others tramping about the polar areas or driving snowcats and setting up permanent camps, along with regular cruise ships visiting with hundreds of humans breathing CO2 all over the ice caps, have something to do with loss of ice? It must have some effect if not switching off a light when leaving a room is soon to be a criminal act.

  67. @Troels Halken. Love it when engineers show up.
    My 2001 model Garmin handheld GPS has consistently been accurate to within 1 meter. When I hunt in the mountains of Montana, I stand beside my vehicle, record its location on the GPS, turn off the GPS, throw it in my pack and go. From time to time I record other waypoints. When it’s time to return to the vehicle, usually after dark, I get the GPS a clear view of the sky and tell it to go to the truck. Haven’t missed the truck yet. Haven’t walked off any cliffs either. Don’t try this without also carrying a map and compass. No sense in becoming a statistic.

  68. Dave Middleton (13:41:59) :

    “There’s something bugging me about the concept of Post Glacial Rebound (PGR) in Antarctica…

    “If Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum,” several thousand years of ice deposition should be missing from the Votok and other ice cores starting in the Holocene… But there isn’t any missing section.”

    Dave, I think you’re missing something here. Just because there’s less ice over Antarctica now than during the Last Glacial Maximum does not mean that an entire layer of ice just melted away. I don’t think ice ever melts in the interior of Antarctica. What happens is, the weight of ice from later years compresses the ice below it and pushes the edges outwards toward the coasts, where it eventually calves off and becomes icebergs. But some portion of the ice from each year remains, buried under tens of thousands of years of additional ice, in the interior of the continent. During the Last Glacial Maximum, the water surrounding Antarctica was cold enough that the ice didn’t calve off as much, so the extent of the ice became greater. But also, the larger extent allowed the ice in the interior to build itself deeper. When the Last Glacial Maximum ended, the ice didn’t just melt away from the interior. Instead, rising water temperatures of the oceans surrounding Antarctica caused more of the coastal ice to melt, and break off. The smaller extent of the ice sheet could no longer support the tremendous weight of ice on top of the continent, and so everything spread out more, which, of course, exposed more ice to the coastal areas, where it too could melt. Eventually, the warming that ended the LGM caused the total extent and depth of ice over Antarctica to decrease significantly, but NOT by melting large volumes of ice in the interior.

    Does that make more sense?

  69. Re: tallbloke (20:51:20)
    There will be updates to that page (unless some kind of unwelcome interference prevents them…)

  70. jeez (22:04:13) :
    Trevor:

    From the article linked to by Lucy above.

    Water-logged sea ice also may explain why sea ice in the Antarctic is increasing. This occurs when the weight of accumulated snow presses down on a slab of sea ice until it’s nearly submerged. When that happens, waves cause ocean water to spill on top of the ice and into the snow, forming a layer that eventually freezes and becomes “snow ice.”
    So, global warming is not only thought responsible for the melting of Arctic ice over the last few decades, but the observed increase in the ice at Antarctica, too.

    Anybody have any idea how much snow cover would be necessary to nearly submerge floating sea ice? My impression is that even in coastal areas snowfall annually is in the 2’to3′ range, which at the temperatures of Antarctica would be equivalent to maybe 2 or 3 inches of water or less. This wouldn’t seem to provide enough mass to submerge sea ice.

  71. Since when has GPS been able to measure anything down the the millimeter level? I have no doubt there is a post glacial rebound…I just question the accuracy of the measurements.

    The capability has existed for a long time. I worked a surveying project over twenty years ago, establishing baselines at closed landfill sites for MNPCA,that was speced at 5mm+/- 3ppm. We used 4 units which cost about $100K each[ two on known reference points, two on the unknowns ] with 1 hour occupation times and about 2 weeks of post processing of the data. Newer equipment and techniques make it faster, but still require fairly sophisticated and specialized skills to achieve that level of accuracy.

Comments are closed.