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Post by marchesarosa on Sept 6, 2010 20:51:16 GMT 1
From Thomas Fuller, WUWT Re the GRACE paper: The paper referred to ..says the Eastern Antarctic has lost 57 billion tons a year–plus or minus 52 billion tons. Hmm. I think we need a few more orbits, myself. Having a margin of error as large as the original figure doesn’t inspire confidence. ... You can always tell when they’re trying to scare you–they talk about firm figures for how much ice is melting, without the data needed to put it into perspective. 57 billion tons certainly sounds like a lot of ice. However, as a percentage of the total it is not even an asterisk. Antarctica has 150 million billion tons of ice… Do you remember that iceberg that calved off Antarctica in March? (Calving is a perfectly normal event, and has nothing to do with climate change.) The one the size of Rhode Island? It was estimated at 860 billion tons. “A 2008 study estimated that Antarctica loses about 1.6 trillion metric tons of ice each year, but gets nearly that much back as annual snowfall. The icy continent may suffer a net ice loss of about 100-200 billion metric tons per year, but Scambos said the exact figure remains uncertain.” (Live Science, Is Antarctica Falling Apart? March, 2010). In essence, what we have here is a new satellite using new tools to take measurements. The data recovered is analyzed using guesses and inferences. Their analysis is presented with a margin of error as large as the amount of ice they say is melting from Antarctica. The loss is is less than 1% of the normal annual melt. Other measurements, consistent with climate theory, have consistently shown the Antarctic gaining, not losing ice. wattsupwiththat.com/2010/09/06/grace-under-fire/#more-24490See, Havelock, even the SCIENTISTS are unclear what is happening. So long as THEY are uncertain I take it that it is OK for ME to be uncertain, too.
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Post by lazarus on Sept 7, 2010 0:35:33 GMT 1
Hold on a sec ... yep I think I've spotted the problem.
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Post by lazarus on Sept 7, 2010 0:44:11 GMT 1
Mary,
What paper is Tom (I’m not a scientist and do not claim to know) Fuller referring to? It isn't clear from this unqualified blog but I suspect it has been taken out of context.
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Post by marchesarosa on Sept 7, 2010 1:17:21 GMT 1
It has been discussed on the WUWT blog you so despise since 20th July. Looks like several teams are looking at the same GRACE data. GRACE’s warts – new peer reviewed paper suggests errors and adjustments may be largewattsupwiththat.com/2010/07/20/graces-warts-new-peer-reviewed-paper-suggests-errors-and-adjustments-may-be-large/Quinn, K.J. and Ponte, R.M. 2010. Uncertainty in ocean mass trends from GRACE. Geophysical Journal International 181: 762-768. There is also this press release Melting rate icecaps Greenland and Western Antarctica lower than expected02 September 2010 by M&C The Greenland and West Antarctic ice caps are melting at half the speed previously predicted. This finding has emerged from research by a joint US/Dutch team from the Jet Propulsion Laboratory, TU Delft and SRON. The scientists have published their findings in the September issue of Nature Geoscience. www.tudelft.nl/live/pagina.jsp?id=7a6c3d15-1c1e-4869-b378-840a000c6803&lang=en
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Post by marchesarosa on Sept 7, 2010 1:46:45 GMT 1
Lazarus
Why did you not highlight the previous sentence in the abstract you quoted - which is the source of the uncertainty that the other papers discuss?
As both present-day changes in the ice/water thickness and glacial isostatic adjustment affect space geodetic measurements, it is difficult to untangle the relative contributions of these two processes.
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Post by marchesarosa on Sept 7, 2010 1:56:25 GMT 1
I think Tom's article refers to the Paper whose abstract you quoted. You are right, he does not quote the name of the paper. He should have. They usually do. But Anthony Watts gave the details of the other two papers I linked to on WUWT, the first as early as 20 July and I linked to it in a post of mine on the BBC Science Bpard a while back.
The Grace Satellite was not properly calibrated at first and sources of error were identified. GRACE uses gravity measurements as a proxy for isostatic rebound, if I remember rightly.
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Post by lazarus on Sept 7, 2010 1:57:31 GMT 1
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Post by havelock on Sept 7, 2010 9:26:51 GMT 1
Did you read the abstract of their actual paper? (http://www.nature.com/ngeo/journal/v3/n9/full/ngeo938.html ) "Global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous. The viscoelastic solid Earth has been responding to this unloading of large ice masses with a rise of the land masses, in a process termed glacial isostatic adjustment. In addition, significant changes in the land/ocean water distribution occur at present. As both present-day changes in the ice/water thickness and glacial isostatic adjustment affect space geodetic measurements, it is difficult to untangle the relative contributions of these two processes. Here we combine gravity measurements and geodetic data of surface movement with a data-assimilating model of ocean bottom pressure to simultaneously estimate present-day water transport and glacial isostatic adjustment. We determine their separate contributions to movements in the geocentre, which occur in response to changes in the Earth’s mass distribution, with uncertainties below 0.1 mm yr−1. According to our estimates, mass losses between 2002 and 2008 in Greenland, Alaska/Yukon and West Antarctica are 104±23, 101±23 and 64±32 Gt yr−1, respectively. Our estimates of glacial isostatic adjustment indicate a large geocentre velocity of −0.72±0.06 mm yr−1 in the polar direction. We conclude that a significant revision of the present estimates of glacial isostatic adjustments and land–ocean water exchange is required." I'm glad to see that you now recognise the value of models in climate science. Marchesarosa - you are aware that the paper that discusses the loss of ice at the arctic is using models to estimate that the loss is half the rate predicted aren't you? Do you accept that models have their place in climate science?
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Post by rsmith7 on Sept 7, 2010 9:56:44 GMT 1
"Do you accept that models have their place in climate science?"
Yes....as long as they're viewed as the flimsy extrapolation tools they are - and the raw data is accurate and uncorrupted - which it isn't. Slingo, the Met Office guru admitted it was "exactly the same models they use for weather forecasting" that they used for climate forecasting. I nearly fell off my chair. Met office weather forecast: 24hrs - pretty accurate 48hrs - pretty iffy 72hrs - very iffy 96hrs+ - rollocks
Yet they use this model to predict 100 years from now. Comedy gold....if it weren't so serious.
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Post by marchesarosa on Sept 7, 2010 10:48:40 GMT 1
msg 22 Havelock Yes, I am aware the GRACE data is supposed to be “calibrated” by means of models. We are back to the same old problem. Are the models reliable? GRACE may or may not provide the best data there is about ice mass in Antarctica but what about all the “adjustments” that are subsequently made to them which are made upon assumptions and not upon observations? It’s a mess! People spin the results whatever way they wish. From the comments on WUWT “The big problem here is that the satellite data has to be adjusted for mantel rebound from the last glaciation 12,000 years ago. Guess how this is done ? A computer model of course. Based on fairly naive , simplistic models about viscosity of the underlying rock etc. These models are total speculation since there is no hard evidence against which to calibrate them. There may or may not be some teething troubles with the satellites but if I wanted to doubt the results of these claims I would look at the models first. These claims are not made “based on satellite data” they are based on pure speculation from uncalibrated models.” Models are only as good as the assumption fed into them. GIGO. Mr Smith has it right. The important point that Tom Fuller was making here wattsupwiththat.com/2010/09/06/grace-under-fire/#more-24490 is not concerned with the accuracy of the adjustment models per se, however, but that the massive and frightening NUMBERS that are bandied about re ice loss (and gain) are meaningless without stating the whole that they are being compared with. 52 billion tons of ice is only a tiny fraction of what is lost when an iceshelf calves. It is an even tinier fraction of the annual replenishment of snow on Antarctica or the annual loss and gain of ice. It is a fleabite of no immediate concern to anyone; of no immediate concern for thousands of years in fact even if it WERE true! Yet the scaremongers jump on it. Fuller is just providing the counterbalance. What are they getting into bed about? as my mother would say.
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Post by havelock on Sept 7, 2010 10:55:19 GMT 1
marchesarosa - you seem to have misunderstood my point. I am not commenting on postings on a blog but on the actual science and would appreciate your views on this aspect. I was not referring to the calibration of GRACE using models but the models used in the paper (whose abstract I quoted) that have estimated the slower rate of ice loss. The specific phrase is "Here we combine gravity measurements and geodetic data of surface movement with a data-assimilating model of ocean bottom pressure to simultaneously estimate present-day water transport and glacial isostatic adjustment." It is the model of the ocean bottom that has led them to believe that the ice loss rate is not as rapid as was thought.I believe that this is good news (shame that the ice is still shrinking) - do you also believe this model based research is portraying an accurate picture? [editted to include link to actual abstract www.nature.com/ngeo/journal/v3/n9/full/ngeo938.html]
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Post by marchesarosa on Sept 7, 2010 18:13:28 GMT 1
"do you also believe this model based research is portraying an accurate picture?"
We are told that the latest version of estimated ice-loss is only half that of the previous.
Since we don't "know" in any real sense what the previous estimate was, what difference does it make that the ice loss is now deemed only half what it was before?
Ice melts, refreezes and it snows. That's all we know for sure.
I don't really bother about it. It is not a matter that preoccupies me. Especially when, thanks to the people who take the trouble to express the purported ice loss in term of the TOTAL mass of the ice-cap, we learn that it is an infinitesimal amount. A mere flea bite.
I think people who try to model change in such a massive geographical feature are on a hiding to nothing. They could be more profitably employed, surely?
I know we should be "pleased" that the purported ice lose is "less", but basically, it is only the model that has changed NOT the reality, isn't it?
Sea level rise has not accelerated noticeably recently by accounts from round the world. It is more or less the same tiny annual increase as it has been since measurement began and can easily be coped with. Coast and harbour infrastructures are replaced over time whether or not the sea level rises. We will cope.
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Post by lazarus on Sept 8, 2010 2:07:11 GMT 1
We are told that the latest version of estimated ice-loss is only half that of the previous. Mary I think you have missed the point of this paper. It is only concerned with measurements from GRACE which measures gravity. Models try to calculate ice mass and loss by changes in gravity. This is quite a difficult thing to do because as the ice is lost the ground rebounds. But GRACE is not the only system of measurement, ICEsat 1 & 2, Radar and laser measurements etc. Here is one method; www.awi.de/en/news/press_releases/detail/item/tifex/?cHash=9cfde6812f66a39d2a276fee728ba986All come to the same conclusion, that the ice is melting and they are very certain of the reason why. But the real point is that the 2007 IPCC predictions for sea level rise did NOT include figures for melting ice cap because there was too much uncertainty at the time. That is why sea level rise has actually been greater than IPCC predictions. By the next report, with the help of such research such as you mention, hopefully the estimates for sea level rise will be more accurate.
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Post by louise on Feb 28, 2011 17:36:26 GMT 1
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Post by Progenitor A on Feb 28, 2011 17:57:49 GMT 1
How fast were they going before? If thet are going faster, could it be because there is a greater mass pressing downhill?
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