tag:blogger.com,1999:blog-8524070301101240472.post3920530421743606724..comments2023-09-28T08:13:11.489-07:00Comments on Only In It For The Gold: Eschenbach has Half a PointMichael Tobishttp://www.blogger.com/profile/08229460438349093944noreply@blogger.comBlogger27125tag:blogger.com,1999:blog-8524070301101240472.post-2910226565067251942013-10-18T03:10:58.361-07:002013-10-18T03:10:58.361-07:00You may find this interesting,
Who is Willis Esch...You may find this interesting,<br /><br /><a href="http://www.populartechnology.net/2013/10/who-is-willis-eschenbach.html" rel="nofollow">Who is Willis Eschenbach?</a><br /><br />As of 2012 Mr. Eschenbach has been employed as a House Carpenter.<br /><br />He is not a “computer modeler”, he is not an “engineer” and he is certainly not a “scientist” (despite all ridiculous claims to the contrary).<br /><br />"A final question, one asked on Judith Curry’s blog a year ago by a real scientist, Willis Eschenbach…"Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-49582752307477234212010-06-03T01:56:39.329-07:002010-06-03T01:56:39.329-07:00Martin said...
Willis, you'll have to spell it...Martin said...<br /><em>Willis, you'll have to spell it out for me...</em><br /><br />Sure. The effective sample size is equal to:<br /><br />n_eff = n * (1 - r - .068/sqrt(n)) / (1 + r + .068/sqrt(n))<br /><br />where "n" is the sample size and "r" is the lag-one autocorrelation. As autocorrelation goes up, the effective sample size (and thus the number of degrees of freedom) goes down.Willis Eschenbachhttps://www.blogger.com/profile/14276840691598976175noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-74506857712590242932010-05-31T00:20:45.422-07:002010-05-31T00:20:45.422-07:00Willis, you'll have to spell it out for me...Willis, you'll have to spell it out for me...Martin Vermeerhttps://www.blogger.com/profile/04537045395760606324noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-58013218842661997642010-05-29T02:56:55.422-07:002010-05-29T02:56:55.422-07:00Martin said...
Willis, Michael, I agree. BTW Willi...Martin said...<br /><em>Willis, Michael, I agree. BTW Willis I don't know where you got DoF = 1 from. Michael's estimate based on the smoothing she is seen to be doing, makes sense although it is an upper bound... I would think n/6 though.</em><br /><br />I got it from the paper that I cited. Please read the Nychka section, which spells out the exact details.Willis Eschenbachhttps://www.blogger.com/profile/14276840691598976175noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-46675678011734614002010-05-27T18:49:47.720-07:002010-05-27T18:49:47.720-07:00Mark, well yes, precisely my point. But if one int...Mark, well yes, precisely my point. But if one interprets the acceleration seen as climatological -- i.e., a small part of a much longer global warming trend -- then such extrapolation would make some sense. And reduces to absurdity.<br /><br />Or do you object to using a quadratic rather than, e.g., a physically more sensible exponential (which would give higher values still)? Yes, then I agree. I am reminded of Loehle's latest CO2 thingy.Martin Vermeerhttps://www.blogger.com/profile/04537045395760606324noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-58779607526073167532010-05-27T14:11:02.776-07:002010-05-27T14:11:02.776-07:00Martin, I agree with everything you say except thi...Martin, I agree with everything you say except this<br /><br />"Another thing I have a problem with is the estimate of 0.17 +/- 0.05 mm/yr^2 she gives for the combined effect of Greenland and Antarctica. That would produce 1.4 meters by 2100... without even looking at the other contributions. I don't buy it."<br /><br />That would only be true if you extrapolated the quadratic to 2100. Why would anyone extrapolate a quadratic fit based on a sample of 7 years of data out to 91 years beyond the sample end-points? In either direction?!Markhttps://www.blogger.com/profile/16914264739638166750noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-17738692114588940142010-05-27T10:54:26.434-07:002010-05-27T10:54:26.434-07:00Actually, if one posts a good idea here, some hung...Actually, if one posts a good idea here, some hungry grad student will see it, write it up, and publish.Aaronhttps://www.blogger.com/profile/05150805906414546377noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-46188649508904657192010-05-27T00:47:10.882-07:002010-05-27T00:47:10.882-07:00Willis, Michael, I agree. BTW Willis I don't k...Willis, Michael, I agree. BTW Willis I don't know where you got DoF = 1 from. Michael's estimate based on the smoothing she is seen to be doing, makes sense although it is an upper bound... I would think n/6 though.<br /><br />One way to get an idea of the number of DoF in the data is to look at the residuals (relative to the parabolic fit) and see how often they wiggle between positive and negative.<br /><br />Another thing I have a problem with is the estimate of 0.17 +/- 0.05 mm/yr^2 she gives for the combined effect of Greenland and Antarctica. That would produce 1.4 meters by 2100... without even looking at the other contributions. I don't buy it.<br /><br />About submitting a comment, why not. And why not together with an experienced scientist, might improve your luck. It is important to get things like this in the record. Alternatively, write <br />to Isabella, she might consider a corrigendum.<br /><br />We (scientists) always criticize contrarians for not doing science, but when they try, and happen onto something, I think we have a duty to acknowledge it. Who knows, the attitude might be contagious.Martin Vermeerhttps://www.blogger.com/profile/04537045395760606324noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-79216412645294691082010-05-26T22:41:09.181-07:002010-05-26T22:41:09.181-07:00Willis' suggested explanation is exactly where...Willis' suggested explanation is exactly where I would look. <br /><br />I suspect, specifically, that they are treating the smoothed series as having n degrees of freedom whereas it ought to have (I think) n/12.Michael Tobishttps://www.blogger.com/profile/08229460438349093944noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-48078424821608281962010-05-26T22:24:28.630-07:002010-05-26T22:24:28.630-07:00Mark said...
Willis, you claim that for the "...Mark said...<br /><em>Willis, you claim that for the "the overall record is so short (six years) that there is no statistically significant difference between a quadratic and a linear fit. Thus we cannot yet say if there is acceleration."<br /><br />However in the 2009 paper <br /><br />http://www.agu.org/journals/gl/gl0919/2009GL040222/<br /><br />Velicogna considered the statistical significance of the acceleration<br /><br />"[17] To verify that the improvement obtained with the quadratic model is significant we used an F-test [e.g., Berry and Feldman, 1985]. The F-test show that the improvement obtained with the quadratic fit is statistical significant at a very high confidence level (99%)."<br /><br />If you can see something seriously wrong with that I suggest you submit a comment to GRL.</em><br /><br />I haven't had much luck, despite very good statisticians agreeing with me, with comments to GRL. However, let me go over the problem.<br /><br />Velicogna et al. figure their statistics based on their fit with the "filtered" data. This is the data shown in red in Figure 1 of their paper. Unfortunately, they have ignored the effect of autocorrelation on their statistics. The filtered series that they use is extremely autocorrelated, which means that their statistics are extremely wrong.<br /><br />Michael Tobis, you say:<br /><br /><em>[Willis] shows no signs of having the statistical skills to take this on. It wouldn't help me personally nor would it add credibility to any point I was trying to make.</em><br /><br />You need to be cautious about your estimation of the skills of people you have never met. In particular, you, and the authors of the paper, should take a hard read of Doug Nychka's paper, ""Confidence intervals for trend estimates with autocorrelated observations" available <a href="http://homepage.mac.com/williseschenbach/.Public/Nychka_autocorr.pdf" rel="nofollow"><b>here</b></a>.<br /><br /><br />The short version is that autocorrelation reduces the number of degrees of freedom. Doing a filter like Velicogna et al. did reduced the number of degrees of freedom in their test data to approximately ... 1. As a result, their tests are meaningless. They used the right test (an F-test on the adjusted R^2 values), but they used 74 (and 73) degrees of freedom in the test, which gave them an incorrect answer.<br /><br />w.Willis Eschenbachhttps://www.blogger.com/profile/14276840691598976175noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-87422702570460496372010-05-26T18:25:56.791-07:002010-05-26T18:25:56.791-07:00No, MT, I'm not really suggesting that you and...No, MT, I'm not really suggesting that you and Willis co-author a paper. Velicogna presents evidence for accelerating mass loss from Greenland and Antarctica in the period 2002-2009. I am not competent to assess the statistical analysis, but they look convincing to a non-expert like me and have passed peer review. Therefore I am inclined to accept her finding, notwithstanding expressions of casual skepticism from you and Willis.<br /><br />(I would make the comment that a lot of the variability in the mass vs time plots is a seasonal variation, which can be removed, Doubtless there are statistical traps and subtleties in such a removal.)<br /><br />Velicogna's analysis is based entirely on the short time series she has available. The acceleration may continue in the future or it may not. This analysis on its own cannot tell us which is the more likely.Markhttps://www.blogger.com/profile/16914264739638166750noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-23324227108675568072010-05-26T08:11:20.498-07:002010-05-26T08:11:20.498-07:00Willis' point and my original half-approval we...Willis' point and my original half-approval were about the existing scale of the melt, not about acceleration.<br /><br />I think the GRACE record by itself looks unconvincing as evidence of acceleration. I find V's point 17 surprising and probably ought to roll up my sleeves and look into it.<br /><br />I think there's little doubt that there is acceleration, but still the actual acceleration, i.e., a quantitative measure of the second derivative of mass vs time, is very uncertain. <br /><br />The early data is very coarse but indeed supports this point of view as Paul suggests.Michael Tobishttps://www.blogger.com/profile/08229460438349093944noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-21012581712364211042010-05-26T07:53:48.323-07:002010-05-26T07:53:48.323-07:00The works cited by Skeptical Science in my comment...The works cited by Skeptical Science in my comment above show clear (to me at least) GPS evidence of acceleration in isostatic rebound starting in 1990 which they relate to GRACE and find consistent with mass loss. Does this have any bearing on the statistical analysis you and willis find questionable? <br /><br />Paul MiddentsPaulhttps://www.blogger.com/profile/13742905742181959851noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-33938015326799739352010-05-26T06:42:26.909-07:002010-05-26T06:42:26.909-07:00Let me try to make it clear.
Willis wants us not t...Let me try to make it clear.<br />Willis wants us not to worry. <br /><br />I <em>don't</em> want us not to worry.<br /><br />Both of us, and Martin who has been a very perceptive commentator here in the past, think the GRACE record is too short to indicate acceleration.<br /><br />The paper itself claims that the record is sufficient.<br /><br />I am not particularly expert in this flavor of statistics. (It's not the way Norbert Wiener used statistics at all.)<br /><br />I think many scientists, in our field as well as many others, tend to be too cook-booky about how to use statistics. I suspect this may be a case in point.<br /><br />Do I intend to coauthor a comment with Willis? Seriously? <br /><br />No. He shows no signs of having the statistical skills to take this on. It wouldn't help me personally nor would it add credibility to any point I was trying to make.<br /><br />Please understand that whether the claim in V's point 17 is valid or not is pretty much orthogonal to whether we should worry about acceleration in Greenland. <br /><br />I agree 100% with what Martin said above.Michael Tobishttps://www.blogger.com/profile/08229460438349093944noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-20329580398827890322010-05-26T04:51:00.014-07:002010-05-26T04:51:00.014-07:00Michael,
there could well be statistically signif...Michael,<br /><br />there could well be statistically significant acceleration on a six year time scale -- but that wouldn't be climatologically relevant. It would be natural variability. And I suspect it would go away if the autcorrelation structure of the data were properly taken into account.<br /><br />The only significant thing that GRACE can give us from this one short mission is the rate of mass loss itself, assuming it was zero before AGW started in earnest. Say this amounts to 0.5 mm of sea level per year. That is 5 cm per century, or 12000 years to melt all of Greenland -- as Willis says. Now of course we have at present 0.8C above pre-industrial. If temps stay constant at that level, then also the rate of melt will stay constant; but you know and I know that that's not going to happen. And then we're looking at decimetres by 2100, for Greenland alone.<br /><br />The nonlinearity of this is decadal. We're gonna need that GRACE follow-up mission.Martin Vermeerhttps://www.blogger.com/profile/04537045395760606324noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-10902434347043472702010-05-25T21:47:16.100-07:002010-05-25T21:47:16.100-07:00So, MT, you'll be a co-author on Willis's ...So, MT, you'll be a co-author on Willis's comment? :-) It's a bit beyond me, I'm afraid.Markhttps://www.blogger.com/profile/16914264739638166750noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-65709490291639350072010-05-25T19:47:03.503-07:002010-05-25T19:47:03.503-07:00I really have my doubts about the statistical anal...I really have my doubts about the statistical analysis in this paper. <br /><br />Of course we expect acceleration on the basis of our understanding of the physics of the situation. But that's not what this flavor of statistics is about. It's about just looking at the data. Now, I think that approach is overrated in our field, but that's beside the point. <br /><br />Visually, the "acceleration" is not compelling. Usually the issue with statistics is that the eye sees correlations that aren't there, not the other way around.<br /><br />So I find it peculiar.Michael Tobishttps://www.blogger.com/profile/08229460438349093944noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-29654317531533272702010-05-25T17:27:34.676-07:002010-05-25T17:27:34.676-07:00Willis, you claim that for the "the overall r...Willis, you claim that for the "the overall record is so short (six years) that there is no statistically significant difference between a quadratic and a linear fit. Thus we cannot yet say if there is acceleration."<br /><br />However in the 2009 paper <br /><br />http://www.agu.org/journals/gl/gl0919/2009GL040222/<br /><br />Velicogna considered the statistical significance of the acceleration<br /><br />"[17] To verify that the improvement obtained with the quadratic model is significant we used an F-test [e.g., Berry and Feldman, 1985]. The F-test show that the improvement obtained with the quadratic fit is statistical significant at a very high confidence level (99%)."<br /><br />If you can see something seriously wrong with that I suggest you submit a comment to GRL.Markhttps://www.blogger.com/profile/16914264739638166750noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-1833077137343192252010-05-25T11:46:36.999-07:002010-05-25T11:46:36.999-07:00There's another oddity, which is the differenc...There's another oddity, which is the difference between the Velicogna 2006 and 2010 results. These vary quite widely, with a number of them being fairly small, while others are on the order of 200 gigatonnes.<br /><br />The changes are so large that about half (19 out of 41) of the month to month changes are of different<b> signs </b>in the two datasets.<br /><br />I don't understand this at all. You would think that ocean leakage and PGR would affect all of the months about the same ... but the effect is not constant in any way.<br /><br />Since 200 gigatonnes is about the size of the yearly loss, that's a huge difference. I find this very curious. Anyone have any explanations for that?Willis Eschenbachhttps://www.blogger.com/profile/14276840691598976175noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-77404904440069350502010-05-25T10:45:21.650-07:002010-05-25T10:45:21.650-07:00Michael, first, thanks for your take on my essay. ...Michael, first, thanks for your take on my essay. A few points.<br /><br />First, when someone says "“If this activity in northwest Greenland continues and really accelerates some of the major glaciers in the area — like the Humboldt Glacier and the Peterman Glacier — Greenland’s total ice loss could easily be increased by an additional 50 to 100 cubic kilometers (12 to 24 cubic miles) within a few years”, that's called guessing. There's a couple "ifs" and a "could easily" in there, which means we're no longer talking about facts. Yes, if it continues, and if it really accelerates then loss could easily be increased. But it is equally true to say that if it doesn't continue and if it decelerates that loss could easily be decreased. That's called guessing, and to me has no place in science.<br /><br />Second, the first Velicogna figure says "The results shown here have not been corrected for PGR or for the effects of hydrological or oceanic leakage." So it is not clear exactly how accurate the figures are.<br /><br />Third, per the second Velicogna figure, the apparent (although not significant) acceleration is all in the first two years. For the last four years of the record, there is no apparent acceleration. A quatdratic fit to those years is indistinguishable from a linear fit.<br /><br />Fourth, the overall record is so short (six years) that there is<b> no statistically significant difference between a quadratic and a linear fit.</b> Thus we cannot yet say if there is acceleration. The lineal nature of the last four years of data argues against it. So as you say, acceleration is not a "slam dunk". It will be some years before we can even determine if there is an acceleration or not, much less get an estimate of its size. <br /><br />So it is irresponsible for a scientist to say the loss is accelerating. That is nothing but hype and alarmism. We don't know that it is accelerating, it is just another guess.<br /><br />My point was much simpler, however. Acceleration or not, the size of the ice loss is trivial. <br /><br />All the best,<br /><br />w.Willis Eschenbachhttps://www.blogger.com/profile/14276840691598976175noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-21450443946274990992010-05-24T20:49:17.972-07:002010-05-24T20:49:17.972-07:00Hmm, well, that acceleration may or may not be sta...Hmm, well, that acceleration may or may not be statistically significant but it sure does put WE's assertions on much shakier ground. That's what you get for taking any of those people at face value, Michael.<br /><br />On a related subject, I had been assuming that the ESA GOCE mission, in theory more sensitive than GRACE due to its much lower operating altitude (requiring aerodynamic fins and an ion engine to compensate for atmospheric drag), would be able to add detail to the ice sheet picture either on its own or via interpolation with GRACE data, but according to a paper I just this doesn't seem to be the case. NASA does have a GRACE follow-on planned, but I don't know whether much more can be expected from it. OTOH, given GRACE plus altimeters plus GPS elvation ground-truthing, it seems to me there's enough to support the fundamental conclusions that have been drawn regardin Greenland.<br /><br />Regarding Grist, failing to understand that the real problem is what happens to the volume of ice loss over the next few decades rather than the next few years strikes me as a forgivable lapse unless, like WE, we prefer to avoid admitting there's any problem until we're watching the ice sheet collapse in the rear-view mirror.Steve Bloomhttps://www.blogger.com/profile/12943109973917998380noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-54650513604223036192010-05-24T18:06:38.910-07:002010-05-24T18:06:38.910-07:00The Antarctic ice mass loss appears to be supralin...The Antarctic ice mass loss appears to be supralinear: <b><a href="http://www.desdemonadespair.net/2010/01/graph-of-day-antarctic-ice-mass-loss.html" rel="nofollow">Antarctic Ice Mass Loss, 2002-2009</a></b>Jimhttps://www.blogger.com/profile/07080844313226790538noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-77681468938800362272010-05-24T17:04:34.428-07:002010-05-24T17:04:34.428-07:00Ice is “ice”, not a “glassy substance”. Glass ha...Ice is “ice”, not a “glassy substance”. Glass has a softening point as does ice. However, ice also has an abrupt melting point. You can pave a floor with glass, and it will be smooth, but you will not be able to “ice skate on it”. Ice is different. Ice near its melting point has the rare ability to flash from solid to liquid. Warming ice under pressure can do this just as surely as stepping on to an ice rink with freshly sharpened skates produces a film of water under the skate blades. Warming ice under pressure can result in the rapid formation of cracks in the ice filled with water. Then, the two sides of the crack can move relative to each other with great ease, putting pressure on other parts of the ice, resulting in “ice dynamics.<br /><br />This is a melting point phenomenon. It initiates abruptly. It will not be like anything we have seen when Greenland was colder.<br /><br />While ice is a poor conductor of heat, Greenland is surrounded by water, including streams of water under it and water vapor over it. Water and water vapor are very good at advecting heat. Greenland will come to 0C pretty much all at once (geologically speaking). Already, moulins are marching up its flanks. Models (with gridding) miss this kind localized hydrology.<br /><br />Recently, the top of Greenland was wet. My guess is that this melt season we will see liquid water and moulins on Greenland as high as 3,000 meters (a thousand meters higher than last melt season. Remembering that water falling through a moulin releases heat, we have the rapid warming of the core of Greenland. <br /><br />I am not worried. As long as the Arctic Sea Ice remains intact, I doubt if sea level rise from Greenland will come close to a cm per year. After the Arctic Sea Ice becomes seasonal, then sea level rise from Greenland ice dynamics could easily become several cm per year. However, the Arctic Sea Ice should remain somewhat intact for the next couple of years.Aaronhttps://www.blogger.com/profile/05150805906414546377noreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-76531166001617106962010-05-24T14:42:34.948-07:002010-05-24T14:42:34.948-07:00The mass loss of the Greenland ice sheet accelerat...The mass loss of the Greenland ice sheet accelerated from the 1980's to 2000 as well, this will not be shown by the GRACE measurements but is evident from the size of <a href="http://cires.colorado.edu/science/groups/steffen/greenland/melt2007/2007.jpg" rel="nofollow">melt area </a>. In terms of the <a href="http://glacierchange.wordpress.com/2010/03/27/petermann-glacier/"Petermann Glacier, this is a slow moving thin floating ice tongue than can collapse but not really accelerate much in its lower 80 km which is the floating part.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8524070301101240472.post-50038072148426376472010-05-24T11:33:14.757-07:002010-05-24T11:33:14.757-07:00Yes, or the total mass balance of the ice.
A fair...Yes, or the total mass balance of the ice.<br /><br />A fair point, see the update above.Michael Tobishttps://www.blogger.com/profile/08229460438349093944noreply@blogger.com