tag:blogger.com,1999:blog-8216971263350849959.post7827896769001168168..comments2023-08-07T16:41:49.660+02:00Comments on Die Klimazwiebel: Sea-level riseeduardohttp://www.blogger.com/profile/17725131974182980651noreply@blogger.comBlogger51125tag:blogger.com,1999:blog-8216971263350849959.post-11524885909394000472010-04-17T13:13:16.731+02:002010-04-17T13:13:16.731+02:00Eduardo (#50),
in this case thermal expansion cou...Eduardo (#50),<br /><br />in this case thermal expansion could be modeled as a low pass filter (PT1): a thermal diffusion resistor between the surface at T and the heat capacity of the mixed layer and its mean temperature T_ml. <br /><br />In addition with an inertial model like this there is no obvious need for pre-smoothing data. Let's see how well it fits (hope I find the time soon).wflammehttps://www.blogger.com/profile/18260929727390446009noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-87398207515465867172010-04-15T16:30:51.362+02:002010-04-15T16:30:51.362+02:00@ 48
wflamme,
ja, völlig einverstanden. Viellei...@ 48<br /><br />wflamme,<br /><br />ja, völlig einverstanden. Vielleicht liegt der Knackpunkt beim Wort 'lag'. Ich meine damit, dass die Response nicht unbedingt simultan sein soll, sondern eher verteilt in der Zeit mit einer gewissen Abklingzeit. Ich sehe aber auch nicht, warum der Einfluss von T oder dT/dt erst nach einer Zeitverschiebung sich bemerkbar machen sollte. In diesem Fall sollte man auch nicht vergessen, dass die Daten mit einem ca 30-jährigen low-pass Filter geglättet worden sind, was es noch problematischer macht, von einem 12-jährigen lag zu sprecheneduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-84168859518904111742010-04-15T09:30:33.386+02:002010-04-15T09:30:33.386+02:00@Georg #30
"The improvement due to dT/dt see...@Georg #30<br /><br />"The improvement due to dT/dt seems quite impressing to me and certainly worth to explore."<br /><br />Try to fit the data to this model, which is as arbitrary as the VR one:<br /><br />dH/dt = a log(T/T0) + b arctan(dT/dt)<br /><br />or<br /><br />dH/dt = a (T - T0)^2 + b dT/dt<br /><br />You may find an even better fit, but would it tell you anything about the quality of the model?<br /><br />A model does not necessarily get better because 5 data points can be fitted well to it.Unknownhttps://www.blogger.com/profile/18092055723308277951noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-56875032128855524432010-04-14T18:51:44.888+02:002010-04-14T18:51:44.888+02:00Eduardo (#46)
Ok, aber erstmal reden wir von eine...Eduardo (#46)<br /><br />Ok, aber erstmal reden wir von einem Lag, die Wärme wird an der Oberfläche eingebracht und wird dort in jedem Fall eine Expansion verursachen. Damit wir aber netto erstmal keine Expansion feststellen, muß irgendwo (durch eingebrachte Wärme) Wasser entsprechend kontrahieren. Welches Wasser soll das denn sein? <br />Die Ausdehnung kann zwar kleiner sein, wenn vorwiegend kaltes Wasser erwärmt wird, aber eben nicht Null und erst recht nicht negativ.<br /><br />Zweitens, selbst wenn solches anomalisches Wasser gefunden würde, was sich bei Erwärmung kontrahiert, wie kommt die Wärme von der Oberfläche genau zu diesem Wasser, ohne daß sich das Oberflächenwasser zunächst entsprechend erwärmt?<br /><br />Drittens, welche weitere Magie stellt sicher, daß sich die beiden Effekte Ausdehnung und Kontraktion gegenseitig immer so aufheben, daß man zunächst keine Veränderung zu bemerken glaubt?<br /><br />Viertens stellt der Ausdruck dT(t-tau)/dt ja nichts anderes dar als ein Totzeitglied (Proportionalglied mit verzögerter Antwort). Nach einem Temperatursprung stellt man also eine Weile nichts fest, dann eine entsprechende Volumenveränderung.<br />Das anomale Wasser entwärmt sich also plötzlich wieder und transferiert die Wärme wieder zurück in die oberen Schichten, wo sie die gewünschte (aber verzögerte) Ausdehnung bewirken. Noch mehr Magie.<br /><br />Fünftens findet dieser Rücktransfer von Energie dann so statt, daß sich die erwärmten oberen Schichten irgendwie doch nicht erwärmen, denn nach dem Temperatursprung bleibt die Oberflächentemperatur ja unverändert.<br />Also noch viel mehr Magie.<br /><br />IMO gehört ein kaputter Ansatz geschrottet, nicht kaputtrepariert.wflammehttps://www.blogger.com/profile/18260929727390446009noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-76055866195730764202010-04-14T17:28:32.238+02:002010-04-14T17:28:32.238+02:00@ 46
'IMO ist es ziemlich egal, wie sich die W...@ 46<br />'IMO ist es ziemlich egal, wie sich die Wärmeenergie nun verteilt, wenn man im Wesentlichen von einer temperaturproportionalen Ausdehnung ausgeht ...'<br /><br />In both cases water would expand, but the magnitude may be different, since the expansion coefficient depends on temperature, pressure and salinity. For instance, at 20 C it is 5 times <a href="http://www.kayelaby.npl.co.uk/general_physics/2_7/2_7_9.html" rel="nofollow">larger</a> than at 0 C. So, in theory, it makes a small difference if the whole heat is concentrated in the upper warm layers or penetrates into the colder layers.eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-55155122944967331912010-04-14T15:23:16.918+02:002010-04-14T15:23:16.918+02:00Eduardo,
IMO ist es ziemlich egal, wie sich die W...Eduardo,<br /><br />IMO ist es ziemlich egal, wie sich die Wärmeenergie nun verteilt, wenn man im Wesentlichen von einer temperaturproportionalen Ausdehnung ausgeht ... also ob zB die obersten 100m um 2 Grad wärmer werden oder die obersten 200m um 1 Grad sollte keinen bedeutenden Unterschied machen. <br /><br />Mal hier geguckt:<br />http://ocp.ldeo.columbia.edu/climatekidscorner/whale_dir.shtml<br /><br />Das Temperaturprofil links und das Dichteprofil rechts zeigt keine offensichtlichen Anomalien, das dichteste, tiefste Wasser ist auch das kälteste. Dh egal welches Wasser erwärmt würde, es würde netto immer eine Ausdehnung bewirken, weil es kein Wasser gibt, das sich unterhalb seines Dichteanomaliepunktes befindet und bei dem eine Erwärmung eine Kontraktion bedeuten würde.wflammehttps://www.blogger.com/profile/18260929727390446009noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-55128335653822591812010-04-14T10:35:18.786+02:002010-04-14T10:35:18.786+02:00Danke , Georg. ich hatte es nicht gesehen.
Theore...Danke , Georg. ich hatte es nicht gesehen.<br /><br />Theoretisch koennte doch ein lag zwischen Flux und dH/dt existieren, da die thermische Ausdehung auch vom Druck und T abhängt, und Temperaturänderungen eine gewisse Zeit brauchen würden, um sich in die Tiefe zu verteilen. Im Klimamodell aber ist die Beziehung zwischen Flux und dH/dt in der Tat simultaneduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-78063894108529295892010-04-14T01:47:12.385+02:002010-04-14T01:47:12.385+02:00fyi: r pielke sr. is also criticizing the VR 2009 ...fyi: r pielke sr. is also criticizing the VR 2009 paper http://pielkeclimatesci.wordpress.com/2010/04/13/continued-misconception-of-the-concept-of-heating-in-the-pipeline-in-the-paper-vermeera-and-rahmstorf-2009-titled-global-sea-level-linked-to-global-temperature/gregornoreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-19141186452895763552010-04-13T15:00:18.012+02:002010-04-13T15:00:18.012+02:00Very entertaining thread, indeed!
For me, working ...Very entertaining thread, indeed!<br />For me, working in engineering, it is quite obvious that you don't fit data to a non-physical function if you are planning to extrapolate.<br />If you are going to extrapolate you are infinitely better off with a physical model. If that is not possible, the second choice would be to fit data to a model which at least behaves nicely. Your model must give resonable results with all reasonable inputs. Never use a model with such unphysical behaviour in the extremes.<br /><br />But hey, it's climate science.<br /><br />Jonas B1Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-66856926358925277312010-04-13T13:14:50.545+02:002010-04-13T13:14:50.545+02:00#40 George
The orbital forcing conditions were ve...#40 George<br /><br />The orbital forcing conditions were very different during Eeminan, <br />the summer radiation at 65 N (which is the key variable for an ice age) was about 60-70 W/m**2 higher than it is today. This is the kind of signal you have to have to melt a significant amount of land ice on Greenland. The anthropogenic warming is not even coming near to such a regional signal.corinnahttps://www.blogger.com/profile/04276992257045005331noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-53243322750824113612010-04-13T12:28:43.339+02:002010-04-13T12:28:43.339+02:00A time lag for thermal expansion simply doesn'...A time lag for thermal expansion simply doesn't make sense physically, even for a coarse model. The same applies to a negative value for thermal expansion. AFAIR, the second term should be around 1.5%/K * thickness_mixed_layer.<br /><br />One should fit that and then focus upon improvement of the first term (if at all) IMO.wflammehttps://www.blogger.com/profile/18260929727390446009noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-69440255974318505672010-04-13T12:27:55.059+02:002010-04-13T12:27:55.059+02:00@Eduardo
Yes, ofcourse, I agree. 0.12°C per year ...@Eduardo<br /><br />Yes, ofcourse, I agree. 0.12°C per year is many times the expected trend and apparently far away from the region where the model does something reasonable.<br />You have more experience with such kind of statistical models but isnt it quite normal that you can find parameter intervalls where the models produce crap?<br /><br />@Leigh Jackson<br />Besides of the papers published in the last about 4 years (you can easily google that) for me the key argument are paleo data.<br /><br />The Eemian had a SL about 4-6Meter higher, the change was very fast and probably fueled by Greenland and West Antarctica. <br />Deglaciation from the last glacial maximum had sea level changes in the order of > 1 meter per century. I cannt see why this cant happen today with Greenland. The LGM was about 5°C cooler than today. A middle of the road scenario gives about +2°-3°C end of the century.<br /><br />Furthermore Greenland is even under pre-industrial climate at a place where it shouldnt be. This means the GIS is maintained by its height and albedo at a place where it woulnt grow once its gone. It is therefore unstable.Georg Hoffmannhttp://www.scienceblogs.de/primaklima/noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-44324440687458083402010-04-13T11:44:32.644+02:002010-04-13T11:44:32.644+02:00@ 36
Georg,
would you agree with the following ...@ 36<br /><br />Georg, <br /><br />would you agree with the following calculation? <br />With the parameters a=0.56 cm/yK and b=-4.5 cm/K, we just need to let the global temperature increase exponentially from the equilibrium level T0 with the time constant 0.12 y(-1), about a trippling every 8 years. At that rate, the increase in temperature a(T-T0) exactly cancels the derivative term bdT/dt, so that sea-level rate is zero.eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-16588692941943267152010-04-13T11:26:03.919+02:002010-04-13T11:26:03.919+02:00@Georg H
Rahmstorf applies his model to a period o...@Georg H<br />Rahmstorf applies his model to a period of 1100 years. These approximations matter.<br /><br />As it stands, my paper would have a simple message: "Rahmstorf is a fool." The paper would be rejected because this is not a new finding.<br /><br />I'll see whether I can be more constructive. As it stands, I have identified a number of errors that one would not tolerate in an undergrad paper. I have yet to find a statistically sound estimate of the impact of temperature on sea level.richardtolhttps://www.blogger.com/profile/14239680555557587153noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-39572619101377402162010-04-13T10:40:02.536+02:002010-04-13T10:40:02.536+02:00Georg 36
"If this paper is the only informati...Georg 36<br />"If this paper is the only information we have pointing to sea level rise between 50-150cm I am pretty sure nobody would care about. But it is not."<br /><br />Could you give some examples, please?Leigh Jacksonnoreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-79216566769848920222010-04-13T09:33:44.505+02:002010-04-13T09:33:44.505+02:00@Eduardo
I wouldn't change the statistical mo...@Eduardo<br /><br />I wouldn't change the statistical model and take the formulation without any lag. The model is already at the border of overfitting. So it's certainly safer nt to introduce more parameters.<br /><br />I checked in their program for the predictions (the program is called sealevel_predict.m in their supplemental material). This is what they did:<br /><br />" % This is the aT + bdT/dt expression relative to 1951-1980, where lambda = b/a:<br /> reftemp = mean(magicc_temp(116:156,model,sc,cc))- mean(gisstemp(1:41)); % this aligns all model temps for 1880-1920<br /> magicc_dtemp = magicc_temp(:,model,sc,cc)-reftemp + lambda * rateofipcc(:);<br />"<br /><br />So pretty sure they took in fact your eq. 1 for the prediction (and therefore a negative b).<br /> <br />One question, one remark<br /><br />1) Is there a statistical problem when using just three parameters? Obviously they did some testing on that, but I have no experience what that actually means.<br /><br />2) My understanding/reading of the section with the "new b" and a lag tau has changed a bit. It seems to me that they just looking for a possible explanation for the b value without claiming better statistics and a clearly suprior model. It's just fishing for a reasonable explanation for the negative b. Within the framework of such extremely simplified models that seems still acceptable to me. However, it should be clear that in each of the parameter a,b,tau there are hundreds of physical processes squeezed in with many known/unknown thresholds.<br /><br />3) I agree with your conclusion "In no way would I consider these results as something like a serious projection." but I am not sure if Rahmstorf would disagree entirely with this. If this paper is the only information we have pointing to sea level rise between 50-150cm I am pretty sure nobody would care about. But it is not.Georg Hoffmannhttp://www.scienceblogs.de/primaklima/noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-35230065337982472772010-04-13T09:08:47.828+02:002010-04-13T09:08:47.828+02:00@Richard
I think Eduardo's interpretation is ...@Richard<br /><br />I think Eduardo's interpretation is correct.<br />T-T0 is in fact a small term and S does not depend on absolut temperatures but on small deviations from TO.<br />But if you think that Science and PNAS Editors and Reviewers should be "ashamed" why not writing a coommentary on your Taylor development refutation?Georg Hoffmannhttp://www.scienceblogs.de/primaklima/noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-26144462253462332992010-04-13T08:04:01.315+02:002010-04-13T08:04:01.315+02:00@Georg
dS = S(t)-S(t-1)
It is the discrete time e...@Georg<br />dS = S(t)-S(t-1)<br /><br />It is the discrete time equivalent of dS/dt<br /><br />dS is something entirely different than S(t)-S(0)richardtolhttps://www.blogger.com/profile/14239680555557587153noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-82459616488511908662010-04-13T00:35:54.563+02:002010-04-13T00:35:54.563+02:00@ 32
Georg,
I think you can answer yourself: whic...@ 32<br />Georg,<br /><br />I think you can answer yourself: which value of b would you use ? The one estimated with the climate model data would not include the contribution from ice melting and ice-sheet instability, which is what they are trying to estimate. So it must be the one fitted from observations. Which one? You have to choose a pair (lag,b), so we are in the previous situation. I think they choose b=4.5 cm/K because the fit is r=0.987. A value of b=0 and lag 0 would yield a r=0.95, a value of b=-4.5 cm/K and lag 1 would yield r=0.99. VR and claim that the determination of this maximum is robust using at most 8 samples. However, in the main paper they also say that the value of b and the lag cannot be determined simultaneously. So the value of b is just arbitaryeduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-32277644015638177282010-04-12T23:53:50.735+02:002010-04-12T23:53:50.735+02:00@Eduardo
"my reading of the paper is that the...@Eduardo<br />"my reading of the paper is that they use eq (2) for the sea-level projections."<br /><br />I dont think that's correct. Their paragraph "Projections of Future Sea Level" (page 21530) starts like this:<br /><br />"After Eq. 2 (that is your eq. 1) has passed a 3-fold test with simulated and observed sea-level data, we will apply it to the 21st century by using ..."<br /><br />I thought your critique on introducing the tO was that this adds another parameter into a statistical model with too few data (and degrees of freedon respectively). <br /><br />If they in fact used eq 1 (I mean your 1 and their 2) does that change the statistical reasoning and your critique?Georg Hoffmannhttp://www.scienceblogs.de/primaklima/noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-50163499184762029102010-04-12T23:35:12.280+02:002010-04-12T23:35:12.280+02:00@ 25
Wflamme,
b turns negative when using the obse...@ 25<br />Wflamme,<br />b turns negative when using the observations to fit the statistical model 1. They argue that it is an artifact because now dH/dt is responding to a lagged T and dT/dt. If one uses what they claim is the 'correct lag' then b is positive. <br /><br />My concern is that there is no way of determining the lag and therefore b, from the observations. Their 'goodness of fit', the correlation to observations, just varies in the second decimal place when changing the lag. <br /><br /><br />@ 30 <br />Björn,<br />my reading of the paper is that they use eq (2) for the sea-level projections. The lag, however, would not make a big differences on the long-term - just wait 12 years longer to get the same (T-T0) and dT/dt. The value of b would make a larger difference : b=2.5 or b=4.5, I guess that they took b=4.5 cm/K <br /><br /><br />@ all<br />I also have problems in interpreting physically both models, even more model 2 with the spooky lag. I did not get into that point though. <br /><br />My understanding is that dH/dt is mostly controlled by the net heat flux: if the net heat flux to the ocean is positive, water warms and expands. If the expansion coefficient would be independent of temperature, salinity and pressure, this would be an exact relationship. If the net flux is used to melt land ice, ocean mass also increases. However, the amount of sea-level created by heat-flux into the ocean and very different than the sea-level caused by melting by the same amount of heat. This means that the partition of the net heat flux (ocean or land ice) can cause large changes in the parameters. And this partition will certainly change from the present into the future. This is one point Low and Gregory pointed out. <br /><br />My interpretation of the statistical models is that dH/dt represents the tendency towards a sea-level equilibrium to a putative temperature T0. At this temperature, sea-level would not change; if T is constant but different from T0, ice is melting. The second term, dT/dt would be a proxy for the net heat-flux into the ocean (positive heat flux -> water warms).<br />I think that both terms partially overlap physically: the sea-level restoring movement towards equilibrium with T0 must be driven by a net heat-flux.<br /><br />All in all, I would perhaps consider similar models to play with, always conditioned to a large sample size where I could really test different models in an independent data set. In no way would I consider these results as something like a serious projection.eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-67567446677853468382010-04-12T22:49:47.261+02:002010-04-12T22:49:47.261+02:00@Bjoern
"The amount of ice that can melt is ...@Bjoern<br /><br />"The amount of ice that can melt is finite. There must hence be a leveling off in the increase in H when T >> T0. (The word 'probably' was a polite way to say 'dead sure'.) What exactly now is "T >> T0"? As I said, nobody knows and there is no test in the method applied by VR to find the (systematic) extrapolation error when the response is less than linear."<br /><br />Actually yes, this is shown in the paper (Figure 3 which is the figure above). The model start to fail at a time horizon of about 500 years (and the corresponding T-T0 variations). <br />The improvement due to dT/dt seems quite impressing to me and certainly worth to explore.<br /><br />@Eduardo<br />Is this right that only equation 1 is used in VR09? <br />Eq 2 is just a trial to give some meaning to the negative b, right?Georghttps://www.blogger.com/profile/07807390701146588135noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-47549443486127957712010-04-12T22:25:55.848+02:002010-04-12T22:25:55.848+02:00@Richard
I havent understood your argument until ...@Richard<br /><br />I havent understood your argument until now. Seems trivial to me, but you might correct me.<br /><br />Rahmstorf formula is actually <br /><br />ds=a dT<br /><br />with dT=T-T0 since these are small temperarure changes around the point of developpment.Georghttps://www.blogger.com/profile/07807390701146588135noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-5967771385029047422010-04-12T19:07:41.703+02:002010-04-12T19:07:41.703+02:00@Georg
Suppose
S=f(T)
then the first order Taylor ...@Georg<br />Suppose<br />S=f(T)<br />then the first order Taylor is<br />S=S0 + a(T-T0)<br />taking the first difference<br />dS=a dT<br /><br />Rahmstorf's dS=aT is just wrong, also as an approximation.richardtolhttps://www.blogger.com/profile/14239680555557587153noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-9533326282619609992010-04-12T17:36:14.716+02:002010-04-12T17:36:14.716+02:00eduardo 14
My perspective as a layman is that if t...eduardo 14<br />My perspective as a layman is that if the scientific consensus is that the debate is about whether the sea will rise, at most, 50 cm more or less than 1 metre over the next nine decades, that is more helpful to know than the IPCC 4's blank space on the question.Leigh Jacksonnoreply@blogger.com