tag:blogger.com,1999:blog-8216971263350849959.post3086699689470316748..comments2023-08-07T16:41:49.660+02:00Comments on Die Klimazwiebel: Climate models and the laws of physicseduardohttp://www.blogger.com/profile/17725131974182980651noreply@blogger.comBlogger68125tag:blogger.com,1999:blog-8216971263350849959.post-36800198001910922352010-03-15T12:56:26.478+01:002010-03-15T12:56:26.478+01:00@ 56
Role of clouds in climate sensitivity
Perha...@ 56<br /><br />Role of clouds in climate sensitivity<br /><br />Perhaps I'd rather written that the behavior of clouds mostly determines the difference between models. Other feedbacks, like water vapor and lapse rate, seem to be more in agreement throughout the models.<br />This is an interesting <a href="http://ams.allenpress.com/perlserv/?request=get-document&doi=10.1175%2FJCLI-3243.1#i1520-0442-18-2-237-f01" rel="nofollow">paper</a>. Figure 1 there shows that the response of cloud cover simulated by two models can be opposite. These two models display almost the extremes in climate sensitivity (smallest and largest), in the previous IPCC Report 2001eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-17029878335677646872010-03-15T00:06:16.807+01:002010-03-15T00:06:16.807+01:00@ 66
Björn,
I am not sure whether I understood pr...@ 66<br />Björn,<br /><br />I am not sure whether I understood properly your question about external drivers. The external drivers, what we call forcings, are prescribed in the simulations, they are not calculated interactively by the model. These usually are the solar irradiance, atmospheric concentrations of greenhouse gases, volcanic eruptions or land use. However, the external drivers may depend on the model use. For instance, a climate model that includes a carbon cycle model would accept as external driver the prescribed anthropogenic emissions of CO2. The CO2 would be then distributed in the climate system (atmosphere, ocean, biosphere) interactively, depending on the temperature, precipitation, ocean dynamics, primary production by the biosphere, etc.<br /><br />The simulation plots were prepared by myself. You can access the data <a href="http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php" rel="nofollow">here</a>. They are written in netcdf format, a format quite usual for large climatic data sets. One would need to spend a certain amount of time to get acquainted with the software to handle those data. There are several public software packages. <br />Other than that <a href="http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch10.html" rel="nofollow">last IPCC Report, chapter 10 </a>contains a good collection of plots of climate simulationseduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-35758265475423502282010-03-14T22:43:22.708+01:002010-03-14T22:43:22.708+01:00Thanks, Marco. Very instructive, indeed, to look ...Thanks, Marco. Very instructive, indeed, to look at source data. Quite remarkable are the artefact in Simulation 1 at the lower right corner of the picture, that does not show up in the other Simulations. At closer inspection, there are several regions where the simulations differ by 3°C, although the average tends to be close together.<br /><br />Are there more examples on the net like this?<br /><br />Eduardo: I have read the Greg Holloway paper on ocean modeling by two thirds and i am quite confused. He is looking for an ocean modeling where the entropy does not decrease over time, except external drivers. Is this the right concept? I mean, can you externalize the drivers in an open system to such an extent that they are not considered as a part of the system?<br /><br />Kooitu: Thanks for the very valuable information on climate models. Unfortunately, I can see only the abstract in the PNAS paper. Eduardo has my eMail address, in case you would be ready to send it to me in full text.<br /><br />I will come back to the last three bullet points but need some sleep now.Unknownhttps://www.blogger.com/profile/18092055723308277951noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-27176580948115812472010-03-14T15:07:47.426+01:002010-03-14T15:07:47.426+01:00@Eduardo:
Your link had an inadvertent %22 at the ...@Eduardo:<br />Your link had an inadvertent %22 at the end, giving a dead link. Here is the functional link:<br />http://wires.wiley.com/WileyCDA/WiresArticle/wisId-WCC24.htmlMarcohttps://www.blogger.com/profile/07262670367947223521noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-2022321860600432492010-03-14T11:25:45.661+01:002010-03-14T11:25:45.661+01:00Commenters that may want to have more closer look ...Commenters that may want to have more closer look into climate models may find <a href="http://wires.wiley.com/WileyCDA/WiresArticle/wisId-WCC24.html%22" rel="nofollow">this review by Nanne Weber</a> interestingeduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-29231937228335498582010-03-13T23:48:18.531+01:002010-03-13T23:48:18.531+01:00@ 62
Reiner, I will watch the video with a bit mo...@ 62<br /><br />Reiner, I will watch the video with a bit more time.<br />In geological times, the atmospheric CO2 concentrations has been higher than today. thirty millions years ago, it was roughly 1500 ppm (parts per million), declining to about 400 ppm for the last few millions of years. In the past million years it has oscillated between the glacial value of 180 ppm and the interglacial value of 280 ppm. The glacial-interglacial transitions take place over a few thousands of years. Today the increase from 280 ppm to 380 ppm has occurred in just 100 yearseduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-47986303982443098162010-03-13T22:57:34.030+01:002010-03-13T22:57:34.030+01:00Eduardo 60
Sorry, I know it is a long video, and ...Eduardo 60<br /><br />Sorry, I know it is a long video, and I did not watch all of it. At some point one of the two makes the assertion that CO2 levels have been historically much higher than they are today. I think they refer to a timespan of millions of years though.@ReinerGrundmannhttps://www.blogger.com/profile/12759452975366986236noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-71971572711432935472010-03-13T22:37:22.179+01:002010-03-13T22:37:22.179+01:00Björn would like to see how different are simulati...Björn would like to see how different are simulations started with with different initial conditions but otherwise driven by the same greenhouse gas forcing. <a href="http://coast.gkss.de/staff/zorita/mpi_a2_surftemp.jpg" rel="nofollow">Here</a> you an find the climate change signal simulated by the MPI model under scenario A2. This is one of the most pessimistic scenarios, so the signal-to-noise ratio is large. By noise I mean the variability induced by the different initial conditionseduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-53638247430484888382010-03-13T22:26:56.783+01:002010-03-13T22:26:56.783+01:00@ 59
this is a 1 hour video clip! it will take me...@ 59<br /><br />this is a 1 hour video clip! it will take me some time to answer your question, but perhaps you can phrase it here for our readers as well?eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-12244235244499697352010-03-13T22:03:08.008+01:002010-03-13T22:03:08.008+01:00Eduardo 12
You state historical levels of CO2 have...Eduardo 12<br />You state historical levels of CO2 have never been higher. What do you make of the statements by Lindzen and Dowlatibadi <a href="http://www.tvo.org/TVO/WebObjects/TVO.woa?videoid?71356252001" rel="nofollow">here</a>?<br />Is this a similar problem as with historical temperature records?@ReinerGrundmannhttps://www.blogger.com/profile/12759452975366986236noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-78917243805412574322010-03-13T12:38:49.999+01:002010-03-13T12:38:49.999+01:00Bjorn (#57)
> + Climate models using Reynolds ...Bjorn (#57)<br /><br />> + Climate models using Reynolds equations are non-linear equations up to second order, i.e. quadratic terms.<br /><br />It is not simple. In atmospheric models, we must somehow incorporate the effect of clouds, and various attempts are made. Such sub-grid scale phenomena that we regard as turbulence are expressed as Reynolds terms in the equation of large-scale motion. There are models at various levels of closure, and the second order is one of them.<br /><br />>+ Time steps of integration vary between 15 min. (Kooitu) and 6h (AR4), but are not stable against changes in integration methods and parameters (Eduardo, Corinna).<br /><br />The value of time step is determined by the necessity of computational stability. It is different case by case. I said 15 min. as an example compatible with 100 km horizontal grid interval. Wind speed of 100 m/s is possible, so the time step must be less than 1000 seconds to achieve computational stability.<br /><br />We do not usually output numerical data at all time steps, but monthly or daily statistics. For the coordinated experiments related to IPCC AR4, participants agreed to make output files at the common time intervals, and the shortest of them was 6 hours. For the AR5-related experiments, 3 hours.<br /><br />>+ Climate models can not represent orographic details in oceans and mountains.<br /><br />It can represent coarse-grained orography larger than the grid interval. (In terms of wave length, twice the grid interval, as corinna mentioned.) Effects in smaller scales may be represented like Raynolds stress, but it is a crude approximation.<br /><br />>+ Climate models so far can not reproduce long-term periodical climatic patterns such as the PDO. (I believe this is related with the issue above!)<br /><br />I think, and I said, that they do reproduce PDO. But the phase of the oscillation is usually random (This is a rough expression, technically it should be rather called "chaotic"), so the reproduction is not useful as prediction. But, in cases where we can give a very good initial condition of the state of the ocean, my colleagues find predictability up to several years.<br /><br />T. Mochizuki et al., 2010: Pacific decadal oscillation hindcasts relevant to near-term climate prediction. PNAS, 107, 1833 - 1837.<br />http://www.pnas.org/content/107/5/1833<br /><br />The rest is difficult for me. I think that whether the climate model is ergodic or not has theoretical significance only. The equally difficult but more practically relevant problem is whether we can separate short- and long- time scale phenomena and can cosider the short-term phenomena like Reynolds stress to the long-term phenomena.<br /><br />Ko-1 M. (Kooiti Masuda)Unknownhttps://www.blogger.com/profile/13437041108856598560noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-38669364096148515442010-03-13T11:09:53.830+01:002010-03-13T11:09:53.830+01:00Dear Kooitu,
I liked your sentence "The situ...Dear Kooitu,<br /><br />I liked your sentence "The situation is more complex than the favorite targets of theorists of complex systems." It is for certain that my concerns are of more theoretical nature and it is always the challenge to get the theories right in a practical case. I'll try to read the paper Eduardo was suggesting over the week-end.<br /><br />Summary observations on climate models, please correct me if I am wrong:<br /> + Climate models using Reynolds equations are non-linear equations up to second order, i.e. quadratic terms.<br /> + Time steps of integration vary between 15 min. (Kooitu) and 6h (AR4), but are not stable against changes in integration methods and parameters (Eduardo, Corinna).<br /> + Climate models can not represent orographic details in oceans and mountains.<br /> + Climate models so far can not reproduce long-term periodical climatic patterns such as the PDO. (I believe this is related with the issue above!)<br /> + Climate model prediction capability is not essential in order to compute climate sensitivity (Georg).<br /> + Climate models so far have not displayed non-ergodic behaviour. (Some mathematicians have argued that while a system with ~20 observables may show chaotic behaviour, a system with 200.000 observables might organize itself in predictive, large-scale patterns. Since I have never heard of that idea in the past ten years, I believe that it was a dead end.)<br /> + Relaxation times of climate models are chosen of the order of few years or decades, hence below some of the periodical climate patterns.<br /><br />I would like a new thread to be started with a more thorough discussion of Georgs (#56) claim, but this is not the right place here.Unknownhttps://www.blogger.com/profile/18092055723308277951noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-48156496030147140342010-03-12T06:29:36.731+01:002010-03-12T06:29:36.731+01:00Hola Edu
I havent checked the paper but ONLY the d...Hola Edu<br />I havent checked the paper but ONLY the differences between different broadband radiation schemes are larger than 2*CO2 radiative forcing. Since this was Corinna's criterium we are done with climate modelling independent of problems with cloud modelling.<br /><br />"The behavior of clouds is very determinant of the climate sensitivity. "<br /><br />It is the most important single uncertainty but it doesnt determine climate sensitivity. Again, several W/m2 of differences in energy balance are due alone to the problems with subtropical low level clouds. Though I certainly wished that the models improve there as I wish that there improve in sea ice thickness, representation of Eckman pumping or precipitation in the Indian Monsoon I cannt see why these clouds are now the key in climate modelling.Georg Hoffmannhttp://www.scienceblogs.de/primaklima/noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-8745700816834212822010-03-11T23:31:24.538+01:002010-03-11T23:31:24.538+01:00#Kooiti MASUDA said,48 & Bjorn (#45)
To add:...#Kooiti MASUDA said,48 & Bjorn (#45)<br /><br />To add: The climate models are based on the Reynolds equations, these are develeoped from the Navier-Stokes equations by a perturbation approach, splitting up every variable into a mean and a turbulent disturbance. The resulting equations are equations for the mean (typically interpreted as a mean related to grid resolution, e.g averaged over 200km). These equations include quadratic perturbation terms, which do not vanish after averaging (eg. u´v´). Strictly speaking, these are additional unknowns for which we do not have equations (we can develop some, but they include new unknowns, higher order perturbations ...). This is the turbulence closure problem, which is solved by parameterisation of the turbulent perturbations: we relate them e.g. to the shear in the mean field. We have many different methods in use to parameterise turbulence and the models are actually quite sensitive to the choice of the parameterisation. To find out what actually is done in terms of turbulence parameterisation in the IPCC models is actually quite difficult, there is no documentation of the actual setups in the IPCC report and the runs are unpublished (some might have been published afterwords). However, to my understanding the turbulence parameterisations used in IPCC models are actually extremely simple, but may be others which were directly involved in the IPCC model runs can answer this better.<br /><br />The smallest scale which can be resolved by a numerical model is 2-times the grid resolution, hence a model with 100km resolution must parameterize all phenomena smaller than 200km.corinnahttps://www.blogger.com/profile/04276992257045005331noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-56033563174900313222010-03-11T23:01:57.321+01:002010-03-11T23:01:57.321+01:00#49, Amateur
I guess you refer to their paper
G...#49, Amateur<br /><br />I guess you refer to their paper <br /><br />GLOBAL WARMING: FORECASTS BY SCIENTISTS VERSUS SCIENTIFIC FORECASTS*<br />Kesten C. Green and J. Scott Armstrong<br /> <br />which can be downloaded (as well as another paper, which I have not read)<br />http://www.forecastingprinciples.com/index.php?option=com_content&task=view&id=26&Itemid=129/WarmAudit31.pdf<br /><br />I came across this paper about a year ago and found it also very convincing. It seems that they are experts on research about forecasting and have developed standard principles and procedures to follow for expert forecasting. After reading their paper I had the strong feeling that it is very need for the responsible persons organizing the IPCC process to study their work further and get in contact with experts on forecast research to organize the assessment more professional: We natural scientist tend to be a bit naive in social science, management, policy and decision making and overestimate our ability to be objective generally strongly.<br />However, this is not really my field and I felt not qualified to introduce their work here. May be we should discuss this in a separate thread?corinnahttps://www.blogger.com/profile/04276992257045005331noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-79052722307378139522010-03-11T14:22:35.482+01:002010-03-11T14:22:35.482+01:00@ 45
Dear Björn,
perhaps you may want to have a l...@ 45<br />Dear Björn,<br /><br />perhaps you may want to have a look at this paper on ocean modelling. <br />http://coast.gkss.de/staff/zorita/holloway_SurvGeophys.pdf<br /><br />To my knowledge the dynamical properties of climate models have been seldom studied from this theoretical point of vieweduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-36253624317101331512010-03-11T14:12:52.876+01:002010-03-11T14:12:52.876+01:00@44
Dear Björn,
1) yes, so far all models are wei...@44<br />Dear Björn,<br /><br />1) yes, so far all models are weighted equally to estimate a range of possible temperature responses in the standard IPCC figures. Actually the calculation of these ranges is not very formal: a multiplication of the simulated ranges by all models by a factor. This should represent the limited model sampling, i.e. just 20 , instead of a full model sample covering all sources of uncertainty. It is known that this approach is not optimal, so hopefully the next IPCC report will improve on this.eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-42782443784401232502010-03-11T14:06:09.924+01:002010-03-11T14:06:09.924+01:00@ 43,47
Corinna and Goerg,
I would tend to agree...@ 43,47<br /><br />Corinna and Goerg,<br /><br />I would tend to agree with Corinna here that the simulation of the energy balance is really important. The behavior of clouds is very determinant of the climate sensitivity. If and how cloud cover changes with temperature is one of the big unknowns and it would be reassuring that climate models could reproduce the mean cloud cover and its variability.eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-3992485770394972062010-03-11T14:00:06.130+01:002010-03-11T14:00:06.130+01:00@ 42
TCO,
climate models historically stem from s...@ 42<br />TCO,<br /><br />climate models historically stem from short-term weather prediction models, which is quite reasonable, I think. These models are complicated, so why start from scratch when there was already a tool that could be augmented for longer term climate projections. Later additional submodels were incorporated: ocean, sea-ice, vegetation, carbon cycle, etc.<br /><br />There are also a slight different type of climate models, so called Intermediate Complexity Models, that try to capture the basic elements of climate dynamics by-passing a detailed micro-representation of all processes, but I would say that in the end they are versions of general Circulation models which have been simplified, parametrizing any of the small-scale processes. Parametrizing means here to find a simple closure scheme for the processes that are not resolved explicitly, as in turbulence models.<br /><br />Your comments seem thoughtful. perhaps we need a new model paradigm for the climate system. One problem is that there is to my knowledge no holistic theory of climate, based in basic global conservations or maximization laws, like say entropy production or similar. To define such a model by-passing the description at microlevel would be quite difficult. <br /><br />Also, in the end we would face again the problem of validation. How can a climate model be tested and validated against observations? This applied to all type of climate models.<br /><br />-To reproduce the present mean climate is not enough, as the model can have been overfitted to reproduce the observations. <br />-To compare with short term chaotic weather trajectories does not give any information, since weather is not predictable after a few days, and so models and observations can perfectly provide different answers even if the models are correct. <br />-To compare with longer (centennial) evolutions, which would be driven by external forcings instead of being chaotic is not possible either because we dont have the observations.<br /><br />Ideas are welcome..eduardohttps://www.blogger.com/profile/17725131974182980651noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-91204459794162968012010-03-11T11:01:32.061+01:002010-03-11T11:01:32.061+01:00Dear experts,
In reading on the web about climate...Dear experts,<br /><br />In reading on the web about climate models, more than once I have come across the names of J. Scott Armstrong and K.C. Green. In my layman's eyes they make a lot of sense, esp. when talking about do's and don'ts in model building.<br />However, in your messages on this excellent blog not once mention is made of the two of them. Can anyone of you inform me on the value of their ideas and views, of which a lot can be found on www.theclimatebet.com ? Thanks!Amateurnoreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-45041945867163977762010-03-11T01:41:01.466+01:002010-03-11T01:41:01.466+01:00@Bjorn (#45)
I should first clarify distinction b...@Bjorn (#45)<br /><br />I should first clarify distinction between actual climate models and analogical thinking I made using the concept of chaos.<br /><br />The actual climate model is based on Navier-Stokes equations. Roughly speaking, fluid motion smaller than the resolvable scale (an example for the part of atmosphere: horizontal grid interval 100 km, time step 15 minutes) are treated as something like diffusion. But fluid motion at the scales larger than this are computed explicitly.<br /><br />The representation of weather in climate models is "chaotic" in the sense that growth of small difference in initial condition is compatible with the chaos theory. But it is not sure whether concepts of the chaos theory such as "attractor" are really applicable here. The situation is more complex than the favorite targets of theorists of complex systems.<br /><br />I said that we think that only avarages and covariances of short-time-scale phenomena (weather, sometimes ENSO or PDO) matter to long-time-scale phenomena. This is not an explanation of how climate models work. This is explanation of how we interpret output of climate models.<br /><br />When we have two runs of the same model with slightly different initial conditions, the phase of weather phenomena will likely be different. We often do "ensemble experiments" containing many such runs. By taking averges of many runs, we expect that the effect of peculiarity of each realization is reduced, and that such statistical properties (not explicitly defined) of weather phenomena that are relevant to climate are better represented. This is not a rigorous theory but a working hypothesis.Unknownhttps://www.blogger.com/profile/13437041108856598560noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-74505246071583955922010-03-11T00:47:07.241+01:002010-03-11T00:47:07.241+01:00@Corinna
"I could not identfy top ten models ...@Corinna<br />"I could not identfy top ten models with an error range about 1-1.5 C, may be you can?"<br />I was focusing on ocean results. <br />Yes we can. <br />ECHAM5 looks nice, some others as well. The errors are quite interesting and often linked to subtropical low level clouds. <br /><br />Your criteria as quality control doenst make sense to me. The problems with these clouds above rapidly produce errors of a couple of W/m2. Though I cannt see in what respect exactly this problem affects the ensemble of feedback processes controlling finally the climate sensitivity. <br /><br />If I remember right just using different broad band radiation schemes is adding up to a couple of W/m2 (so just diefferent parameterisation of band width and shape and stuff like this). Only line-by-line models give nearly perfect corroboration.<br /><br />In general I dont think that one single metrik (like SSTs) is a good criteria for a quality control. It is more the connection between different processes and mechanisms.<br /><br />@Bjoern<br />No, the results of simple models are not more reliable. What I wanted to say was that a simple model can obviously easily been tuned to give the right mean temperature. But it's basic physical behaviour (e.g. climate sensitivity) does not depend on having the mean temperature right.Georg Hoffmannhttp://www.scienceblogs.de/primaklima/noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-88548736676447976492010-03-10T22:28:48.627+01:002010-03-10T22:28:48.627+01:00@corinna
Your point on errors over ocean is quite...@corinna<br /><br />Your point on errors over ocean is quite disturbishing but convincing.Unknownhttps://www.blogger.com/profile/18092055723308277951noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-23748435223395820292010-03-10T22:25:16.871+01:002010-03-10T22:25:16.871+01:00@Kooitu Masuda #38
You mentioned that weather is ...@Kooitu Masuda #38<br /><br />You mentioned that weather is chaotic, and I couldn't agree more. The question was, however, whether climate models reproduce chaotic behaviour, not whether the wheather is chaotic. As Anna pointed out recently, it is not the full Navier-Stokes equations but the simplified Reynolds equations that are used for climate models.<br /><br />Let us delve on the type of simplification: The Navier-Stokes equations describe a fluid that is subject to turbulence on each spatial scale. As a consequence, there are no mathematical and no numerical solution to the full Navier-Stokes-Equations, only approximations.<br /><br />Maybe one of the professional climate modelers could comment on what simplifications are actually made. (Unfortunately, I won't be able to do this on my own tonight.)<br /><br />My guess is that the simplifications have to do with cutting off small-scale turbulence. Why I believe so: this would greatly reduce computation complexity.<br /><br />If I am right, it means that exactly the necessary "noise" is thrown away that would otherwise ensure ergodicity, in other words, that "the short-time-scale phenomena affect the long-time-scale phenomena only via their simple statistics such as averages and covariances". In any case, I still think that we are in deep trouble when using models that have not been checked thoroughly for its mathematical behaviour.Unknownhttps://www.blogger.com/profile/18092055723308277951noreply@blogger.comtag:blogger.com,1999:blog-8216971263350849959.post-45110845809630625862010-03-10T21:40:50.412+01:002010-03-10T21:40:50.412+01:00@Eduardo / Georg #39+40
Ad 1)
Not sure whether y...@Eduardo / Georg #39+40<br /><br />Ad 1) <br />Not sure whether you both overlooked the most crucial point, at least in my opinion. "Good" and "bad" GCM were used with equal weights by the IPCC in the AR4 in order to predict climate sensitivity, altogether 23 models with different quality from useful to dreadful waste of time. However, the UNWEIGHTED AVERAGE climate prediction was used by the IPCC in its statement of what is current knowledge in climate sciences. When I first noticed, I got quite upset and thought this procedure is utterly un-scientific.<br /><br />Ad 2) <br />Counter-example: A finite element simulation of a car crash tells you that a crash at 35 km/h does not produce any substantial effects on a certain car type. In the crash test of the corresponding prototype, the car gets fully destroyed, however, at 35 km/h. Would you like to drive that car at 80 km/h?<br /><br />The analogy is that a model should not be trusted to represent valid physics if it is not able to reproduce past climate.<br /><br />Ad 3) <br />Georg, you are fully right. However, the individual model's backtesting results are displayed in the appendix 8 (?) of the AR4, so you could check where exactly a model produced too much warming and where too much cooling. I somewhat share Ed's concerns on open ocean climate backtesting errors.<br /><br />Ad 4)<br />Georg: Are you sure that simpler models could produce more reliable results than complex ones? If CO2 absorbs heat and radiation, there should be a warming effect in the troposphere, a cooling effect in the stratosphere and an increase in (vertical) convection. I doubt whether simple models could help better in modeling vertical convection than sophisticated ones.Unknownhttps://www.blogger.com/profile/18092055723308277951noreply@blogger.com