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How reliable are climate models?

What the science says...

Select a level... Basic Intermediate

Models successfully reproduce temperatures since 1900 globally, by land, in the air and the ocean.

Climate Myth...

Models are unreliable

"[Models] are full of fudge factors that are fitted to the existing climate, so the models more or less agree with the observed data. But there is no reason to believe that the same fudge factors would give the right behaviour in a world with different chemistry, for example in a world with increased CO2 in the atmosphere."  (Freeman Dyson)

Climate models are mathematical representations of the interactions between the atmosphere, oceans, land surface, ice – and the sun. This is clearly a very complex task, so models are built to estimate trends rather than events. For example, a climate model can tell you it will be cold in winter, but it can’t tell you what the temperature will be on a specific day – that’s weather forecasting. Climate trends are weather, averaged out over time - usually 30 years. Trends are important because they eliminate - or "smooth out" - single events that may be extreme, but quite rare.

Climate models have to be tested to find out if they work. We can’t wait for 30 years to see if a model is any good or not; models are tested against the past, against what we know happened. If a model can correctly predict trends from a starting point somewhere in the past, we could expect it to predict with reasonable certainty what might happen in the future.

So all models are first tested in a process called Hindcasting. The models used to predict future global warming can accurately map past climate changes. If they get the past right, there is no reason to think their predictions would be wrong. Testing models against the existing instrumental record suggested CO2 must cause global warming, because the models could not simulate what had already happened unless the extra CO2 was added to the model. All other known forcings are adequate in explaining temperature variations prior to the rise in temperature over the last thirty years, while none of them are capable of explaining the rise in the past thirty years.  CO2 does explain that rise, and explains it completely without any need for additional, as yet unknown forcings.

Where models have been running for sufficient time, they have also been proved to make accurate predictions. For example, the eruption of Mt. Pinatubo allowed modellers to test the accuracy of models by feeding in the data about the eruption. The models successfully predicted the climatic response after the eruption. Models also correctly predicted other effects subsequently confirmed by observation, including greater warming in the Arctic and over land, greater warming at night, and stratospheric cooling.

The climate models, far from being melodramatic, may be conservative in the predictions they produce. For example, here’s a graph of sea level rise:

Observed sea level rise since 1970 from tide gauge data (red) and satellite measurements (blue) compared to model projections for 1990-2010 from the IPCC Third Assessment Report (grey band).  (Source: The Copenhagen Diagnosis, 2009)

Here, the models have understated the problem. In reality, observed sea level is tracking at the upper range of the model projections. There are other examples of models being too conservative, rather than alarmist as some portray them. All models have limits - uncertainties - for they are modelling complex systems. However, all models improve over time, and with increasing sources of real-world information such as satellites, the output of climate models can be constantly refined to increase their power and usefulness.

Climate models have already predicted many of the phenomena for which we now have empirical evidence. Climate models form a reliable guide to potential climate change.

Mainstream climate models have also accurately projected global surface temperature changes.  Climate contrarians have not.

Various global temperature projections by mainstream climate scientists and models, and by climate contrarians, compared to observations by NASA GISS. Created by Dana Nuccitelli.

A 2019 study led by Zeke Hausfather evaluated 17 global surface temperature projections from climate models in studies published between 1970 and 2007.  The authors found "14 out of the 17 model projections indistinguishable from what actually occurred."

There's one chart often used to argue to the contrary, but it's got some serious problems, and ignores most of the data.

Christy Chart

Basic rebuttal written by GPWayne

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Dana Nuccitelli: Principles that models are built on.

Last updated on 9 September 2019 by pattimer. View Archives

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Argument Feedback

Please use this form to let us know about suggested updates to this rebuttal.

Further reading

Carbon Brief on Models

In January 2018, CarbonBrief published a series about climate models which includes the following articles:

Q&A: How do climate models work?
This indepth article explains in detail how scientists use computers to understand our changing climate.

Timeline: The history of climate modelling
Scroll through 50 key moments in the development of climate models over the last almost 100 years.

In-depth: Scientists discuss how to improve climate models
Carbon Brief asked a range of climate scientists what they think the main priorities are for improving climate models over the coming decade.

Guest post: Why clouds hold the key to better climate models
The never-ending and continuous changing nature of clouds has given rise to beautiful poetry, hours of cloud-spotting fun and decades of challenges to climate modellers as Prof Ellie Highwood explains in this article.

Explainer: What climate models tell us about future rainfall
Much of the public discussion around climate change has focused on how much the Earth will warm over the coming century. But climate change is not limited just to temperature; how precipitation – both rain and snow – changes will also have an impact on the global population.


On 21 January 2012, 'the skeptic argument' was revised to correct for some small formatting errors.


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Comments 1201 to 1250 out of 1297:

  1. Deplore_This , yes everyone with reasonable climate knowledge has heard of Dr Judith Curry ( and I myself visit her blog several times a month . . . it's a sort of upmarket version of WUWT  blog ).   Dr Curry's commentary is an excellent object lesson for those who wish to exercise their critical thinking!    She is one of the very very  few climate-contrarian scientists (a dying breed, it appears).

    Now, I notice your rapid-fire uploading of long posts at 1:23 AM and 1:24 AM and 1:25 AM.    Clearly these were pre-selected & prepared to go, and were not really a response to Scaddenp.

    And as you say: "... I've read criticism of the validity of ..."    And there is the nub of your problem, Deplore_This.

    The internal evidence of your many posts, is that you have not bothered to learn the fundamental science of climate yet.  Once you have done so, then you will be able to (A) make an informed decision whether or not to attempt the various complexities of climate modeling (with or without access to a supercomputer)

    . . . and (B) see right through the ludicrous nonsense of "the 500" scientists you mentioned

    . . . and (C) see right through Dr Curry's vague obfuscatory sophistry.

    It is a red-flag sign, that you have allowed yourself to be taken in by the simply unscientific propaganda exhibited by "the 500".    But Dr Curry's propaganda is a different matter ~ she uses a more subtle approach (analogous to what the hypnotherapists call "the Indirect method" ).   If you yourself are strongly motivated to believe her - which indeed you are - then she seems to make sense.   That is, she seems to make sense until you educate yourself past the "veneer" level of climate science.  And then, using skepticism and critical thinking, you will see the fatal flaws in her presentations.

    #  My apologies for sounding patronizing ~ but you really do need to learn the climate science first.   Don't be an Ivar Giaever, who succumbed to Motivated Reasoning, and reckoned that half a day or so on the internet sufficed for him to lecture the climate experts on their multitude of errors.   ( Yes, there are many humorous events to be found in the sphere of climate science ! )


    [TD] I deleted Deplore_This's lengthy cut and paste about Curry, because only a tiny fraction of it was directly relevant to the Models topic of this thread. Despite the baiting that Deplore_This is doing, please let's try to stick to the thread topic. Thanks.

  2. Deplore_This:

    You have now reached the point where moderators are starting to cut stuff.

    You posted a long story from E&E. You are hitting all the main climate denier sites. Well done. You are selecting to quote places that confirm your bias.

    FYI, I started learning about this stuff in the 1970s. I read a lot of the primary literature long before there was an IPCC. I can tell when someone is trying to fool me.

  3. My opinion is that the lady that protest too much might be Curry.

    From the WIKI page on GCMs: "Versions designed for decade to century time scale climate applications were originally created by Syukuro Manabe and Kirk Bryan at the Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, New Jersey.[1]"

    Further:"In 1956, Norman Phillips developed a mathematical model that could realistically depict monthly and seasonal patterns in the troposphere. It became the first successful climate model.[2][3] Following Phillips's work, several groups began working to create GCMs.[4] The first to combine both oceanic and atmospheric processes was developed in the late 1960s at the NOAA Geophysical Fluid Dynamics Laboratory.[1]"

    It is obvious that Fluid Dynamics are at the foundation of all the current coupled atmosphere-ocean GCMs. I find that the dissatisfied search for a specific university course on such models is perhaps disingeneous. They are an area of research, very much at the edge of knowledge. People who participate in them have already obtained graduate degrees in fluid dynamics, applied mathematics and a variety of other fields. I doubt that there are university courses on specific protein folding methods, short of outlining the basic principles and current state og knowledge. However, those who want to orient themselves in that field will easily come across the areas of knwoledge they should master first. Then they can try to go hack it at the cutting edge.

    Curry does a favorite trick of hers by exploiting the fact that GCMs are not very good at delivering regional results, something well known in the modeling community, to suggest that they have no usefulness. In any case, the claim that fluid dynamics expertise is absent in the modeling community has no merit.

  4. Yes, the "search" for a class on "Make your own GCM" is certainly odd.

    I'll bet if I did a search through university catalogues for courses on "How to program a Word Processor", I would not find much at all. To use that as evidence that word processing software is not useful - hey, I"m a word processing skeptic! - would not be an effective argument.

    I could then switch to listing people that have found bugs in word processing programs as evidence that "word processing is not settled", or that "you can't trust word processors".

    Yet somehow, each day people use word processing softare to create all sorts of useful texts. (They seem to create some awful ones, too, but that is another story...)

  5. Bob Loblaw @1204 ,

    The "search" for a course on DIY  GCM's is not just certainly odd  ~ it is positively hilarious.

    But maybe technology is moving faster than I thought.  And I had better check Amazon for stocks of those long-promised pocket-size quantum supercomputers (powered by cold fusion, I hope).   Doubtless these miniaturized marvels would be quite expensive at first ~ but perhaps early adopters will be issued with a bonus App for a GCM or two.

    Our moderator seemed to think that the good Deplore_This  was doing some "baiting" ( aka "trolling" ? ).    Never in a million years would I have thought such a thing . . . but it might explain the underlying motivation of this recent "encounter" at SkS, and it would explain the confused rambling denialism that he/she is throwing up.  And explain the DK-like complacency.

    Phillipe C @ 1203 ,

    your suggestion that the Lady in Question might be the good Dr Curry, is, surely, a tad ungentlemanly?   After all, the literary style is somewhat different ~ though I suppose I could be wrong on that (or the style might have had an extensive makeover per Grammarly or similar App).

    Still, it will be interesting if there are more developments.  I always hope there will be something new to learn, from every "challenge" to mainstream climate science.   Admittedly, my hopes have always been dashed ~ but some day there may be a grain of wisdom to be found among the bucketloads of BS.

  6. Deplore_me. Hmm, some disappointing stuff there - it is very disappointing when the best predictor of person's beliefs on a purely scientific question is which side of the US cultural wars they on - but if you are prepared to invest in courses to get answers, then that is great and makes me hopeful. While I am tempted to respond to your answers, I doubt that would either productive or on topic, so sticking to topic.

    Assuming you get a model by some means and figure out the workings, it would be interesting to know how you would use it. In particular,  what kinds of answers could you imagine your investigations producing that would change your mind. It would be good to be thinking about this and getting the necessary domain knowledge so that you are not misled. Many "skeptics" go after straw-men - trying to take apart claims that modellers and scientists never made. (eg modellers claim no skill in decadal level of prediction). EdGCM would be a good starting point.

    Oh and I am in NZ, working in more or less the equivalent of the USGS though our science structures are very different to US.

  7. @ Eclectic, @Bob Lowlaw, @Philippe Chantreau, The moderator

    Your sophomoric comments memorialize your lack of credibility and reflect poorly on all of the proponents of this website and to some extent to the entire climate science profession. Your adolescent giddiness that you can slander me and the moderator will strike my response that challenges your opinion demonstrates that in your little sandbox here you are not practicing science. If Judith Curry was your Professor I’m sure she’d be embarrassed at your unprofessional and juvenile behavior.

    From my perspective your behavior here demonstrates that she is right “We've lost a generation of climate dynamicists. These are the people who develop theories and dig into data on the system and really try to find out how the system works. We've ceded all that to climate models, and the climate models are nowhere near good enough. The climate models were designed to test sensitivity to CO2. They don't even do a very good job at that…we've lost a generation of climate dynamists, and that's what worries me greatly.”

    And in the end, you’ve all failed to answer my question so what is your reason for being here.

    Good day.

  8. @scaddenp 1206

    Thank you for your response. Candidly a reason for your disappointment evades me. As I stated in my post 1195 to you I’m trying to evaluate the validity of the GCMs referenced by the IPCC against the criticism of scientists like those posted in 1193 and 1194. All I find from the climate science community are responses like those above who merely state your sources aren’t credible, read this and you’ll understand what we do and if you don’t agree with us you’re a flat earther.

    I’m not looking to create a GCM but to understand what they are, their structure, their fidelity and the assumptions that go into the GCMs used by the IPCC. To state it simply I am questioning the validity of the IPCC’s consensus opinion and am trying to find a way to evaluate it myself. I thought that I would take it to the next level and look at the underlying models themselves. I’m not on a career track in the climate science profession I’m merely looking to satisfy my personal curiosity. I thought I would take a university course that climate scientists use to learn the development and use of GCMs and posted here for recommendations. No one here has recommended one yet so I think my only recourse is to contact Penn State and see if course material is available from their last course on GCM.

    BTW I’m in the US retired from the wireless equipment manufacturing business. I visited NZ 20 years ago for a broadband wireless system we supplied. The landscape is remarkable; the emerald green of Ireland painted over the rock of Gibraltar and I found the people friendly (that is once I realized that wearing the shirt of the national rugby team of Scotland was a big mistake).

    Thanks again for your response.

  9. Philippe C , I may have to back-pedal on my skepticism about your Questionable Lady hypothesis.  There does indeed seem to be a Curry worship of almost Sub-Continental dimension.  Perhaps the good Doctor has a Mrs Hyde facet to her personality?

    Deplore_This , your truculence & tone-policing are a red flag.   So much so, that your "search for a GCM course" seems merely a pretext for your postings.

    Yet if you do have a genuine concern about the value of climate models, then please express those concerns in your own words.  Without doing a "cut and paste" from the typically vague and non-substantive rhetoric which is the standard output of Dr Curry.

    You seem not to be aware that the GCM's are not the basis of climate science nor are they the basis of expectations of continued global warming & the consequential major problems.   The basic physics / paleo climate evidence / and the past 150 years of empirical evidence of climate response to rising atmospheric CO2 . . . all combine to give adequate grounds for policymakers to take urgent action to reduce CO2 emissions.

    Climate models can sometimes be used as a test bed for certain sub-components of climate or energy fluxes.  And they can (famously) produce a large range of interesting projections.  But their pragmatic usefulness for projections, is low for the present & near future.

    And that should be very obvious to you, when you take note of the wide range of Equilibrium Climate Sensitivity which is generated by the typical models.   In other words, Deplore_This , you will largely be wasting your time if you pursue "a course in GCM's" .   You really really  do need to study the basic science of climate.

  10. @ Eclectic

    You obviously don't realize that you've just proven the point that I made in my post at 1207.

  11. D_P @1210 ,  alas you are too non-specfic in your reference.

    If you meant "The climate models ... don't even do a good job"  ~ then that is stating the obvious.

  12. 1176 Deplore_This

    You seem to be hitting on the same frustrations I am in regard to getting straight information about the climate models and how they are used. It turns out that you can do a free download of many of the codes used in implementing the climate models, and with the make utilities of most Unix systems (including Linux), actually compile and run them. Don't hold your breath, however, in understanding the "nuts and bolts" of the programs or even how to set up and submit a job on those systems. The only people who get that kind of help are the techie types recently hired by a government contractor specifically to do such number-crunching. 

    Anyway, I will answer your questions as best I can, realizing that I may not know much more about the AGW community than you do. First, I believe that the development and testing of today’s climate models is generally legitimate and done to meet the needs of climate and environmental researchers. Of course, these models were not done single-handedly, but with a team consisting of individuals with several different areas of expertise. Over the decades, they have worked out quite well, and I believe that the statements made by the SkS staff at the top of the page are generally correct.

    However, I believe there is something important concerning these models that the AGW community in general is not telling us. I would like to tell you more, but would rather not do so in this forum. If you are interested please send a message to the (temporary) email address and I will send you a return message from the more “permanent” email account I would like to use.

  13. Eclectic @1174

    Please explain what you mean by the bigger context, and paleological evidence.  Also, please explain how your CO2 "control knob" is supposed to work.


    [TD] Among a huge number of other resources, there is the wonderful and easily understandable 2009 AGU talk by Richard Alley, The Biggest Control Knob: Carbon Dioxide in Earth's Climate History. Steve Easterbrook wrote a good summary, but you really should watch Alley's one hour video. Then read Lacis et al. (2010), Atmospheric CO2: Principal control knob governing Earth's temperature. Alley gave (yet another!) excellent talk six years later, this time just half an hour and to the NAS, 4.6 Billion Years of Earth’s Climate History: The Role of CO2. Among several relevant posts here at SkS is How Do We Know More CO2 Is Causing Warming? Please post your comments in an appropriate thread.

  14. "Candidly a reason for your disappointment evades me." Well the right wing dog whistles and then repeating the GWPF nonsense with claims you should have been able to refute unaided given your IPCC reading had you looked at it critically. 

    I repeat that it is great idea to understand the models, but only if you are going into without the biases of trying to find something which would aid your disbelief and with no clear idea as to what might change your mind. 

    If your preference for Curry is because she expresses similar political belief to yourself and not her publishing record in climate models, then I dont think we have much to discuss, and certainly not on this thread.

  15. It is an interesting thought that somebody who uncritically references both a GWPF publication (ie Briefing Paper No 24) that attempts to trivialise the usefulness of climate models (as @1193) and the 2019 Dutch denialist petition to the UN that attempts to reverse the global consensus on AGW  (as @1194) would somehow obtain a deep enough understanding of the limitations of GCMs to form a useful judgement on ECS from a rather basic course on the subject, especially given that such a judgement could be gained more simply by other means.

    The CLINTEL petiton (CLINTEL is basically an attempt to create a Dutch version of GWPF, the latter having been quite successful in masquerading as an educational charity and finding fertile ground within influential parts of right-wing UK politics) and the GWPF publication both contain the same bold assertion which is fundamental to their denialist argument that GCMs cannot be relied upon.

    "The world has warmed at less than half the originally-predicted rate, and at less than half the rate to be expected on the basis of net anthropogenic forcing and radiative imbalance. It tells us that we are far from understanding climate change." CLINTEL petition.

    "There is growing evidence that climate models are running too hot and that climatesensitivity to carbon dioxide is at the lower end of the range provided by the IPCC." GWPF Briefing Paper No24.

    I would suggest the commenter first considers whether it is correct and proper to present such argument rather than attempting to "get under the hood and see how the models work for myself and to evaluate the predictive sensitivity of these models."

    Operations Research (Operational Research my side of the pond) is only narrowly about the mathematics so I am intrigued that somebody with an "extensive background in operations research" (as per described @1162) would consider 'getting under the hood' as the first response to  having "read criticism of the validity of the climate temperature models referenced by the IPCC."

  16. ClimateDemon @1213 , the bigger context is the paleo evidence ( you can start reading at (SkS) Climate Myths 12 and 13 , and expand out from there.

    The modern empirical evidence ~ a temperature rise of 1 - 1.2 degreesC since industrialization 1850-ish,  all with a 1.4x rise in air CO2 . . . and your own back-of-envelope logarithmic calc extrapolates that to around 2.0 - 2.4 as TCS and hence ECS around 30-40% higher again.   IOW, an ECS of around (roughly) 2.5 -3.5 C.   [Which is way higher than the deluded Lord Moncton "calculates".]    And which also fits with the paleo estimates.

    That all connects well with the "CO2 control knob" (remember to adjust for solar brightening/dimming over time).  Find the right thread, if you wish to comment.

  17. Recommended supplemental reading directly related to the current discussion initiated by Climate Demon...

    Explainer: How the rise and fall of CO2 levels influenced the ice ages by Zeke Hausfather, Carbon Brief, July 2, 2020

    From the article...

    In this explainer, Carbon Brief explores how the last ice age provides strong evidence of the role CO2 plays as a “control knob” for the Earth’s climate. It also acts as a cautionary tale of how the climate can experience large changes from relatively small outside “forcings”.

  18. Steve Easterbrook has written multiple blog posts describing how computerized climate models are designed, built, tested, maintained, and used. I eagerly await his "forthcoming" book, but in the meantime I suggest everyone interested in that topic peruse his blog posts. For example, there is is his post When is a Model Not a Model?

  19. It is important to understand that GCMs are only a small subset of "climate models," and therefore the evidence that "climate models" provide is far broader and deeper than the evidence that GCMs provide. I highly recommend Naomi Oreskes's book Why Should We Trust Science?, for the broad background on those topics beyond climate science, though she does use some examples from climate science.

  20. I take issue with DeploreThis characterization of my post. I re-read it and I find nothing deserving to be called "sophomoric", "adolescent giddiness" and whatever else was in that flurry of name calling. I was not the one referring Shakespeare in the first place.

    A quote from Curry was provided that laments the lack of fluid dynamic expertise in the modeling community. I pointed to the fact, verifiable, that GCMs have originated and are constantly refined in the top fluid dynamic labs of the country. DeploreThis then repeated the same quote without specifying how merely repeating it made any difference. I will add that Curry's characterization is not accurate, as there is plenty of hard physical science contribution to climate science now, and plenty of data crunching people, data papers, etc. Does she provide a breakdown of papers according to "types" of work that she finds less "dynamicist"? All she has is a vague and general statement designed to create a negative perception without, ironically, real world data, to back it up.

    Further I noted that it is disingeneous to ask for a university course on how to makle a GCM because of the nature of the enterprise. I completely stand by that statement. Nobody is going to go to a business school and ask for for a course in "how to make an Amazon-like mega company." That would be the same type of enquiry in a different domain. I am not surprised that it can't be found. Passed all the name calling, hand-waving, self-rightneousness and indignation, I do not see any cogent argument from DeploreThis as to why that would be a valid enquiry.

  21. There may be some interesting points in this paleo evidence and the “bigger context” described by Eclectic, but it’s not really the issue I am trying to address. What I am trying to address are the current arguments for CO2 being the “control-knob” GHG (despite the fact that H2O vapor is the stronger GHG) which subsequently leads to the claim that humans are overheating the earth with their CO2 emissions, and that our very survival depends on government intervention. Now, in every reference I can find, including the Lacis et. al. 2010 paper and this website, the reason given for CO2 being the controlling GHG is that H2O vapor is condensable whereas CO2 is not. Furthermore, it is asserted without clear grounds that the H2O vapor concentration is given by the Clausius-Clapeyron equation at the current temperature, or IOW at 100% relative humidity. With this constraint on the H2O vapor concentration, it can then be only a feedback to temperature changes. CO2, however, has no such constraint and can actually cause temperature changes simply by adding more of it. This is the argument by which CO2 becomes the controlling GHG even though it is the weaker GHG. Note that without somehow constraining H2O vapor to being a feedback only to temperature change, then the entire basis of AGW collapses since H2O would then be the controlling as well as the stronger GHG. Humans may have some control over the amount of atmospheric CO2, but not H2O vapor since over 70% of the earth’s surface is covered with H2O liquid.

    Therefore, we see that the AGW theory stands or falls on whether or not CO2 is the controlling GHG, and I believe I pointed out (in 1173) some serious problems with the arguments in favor of the CO2 “control knob”. If these problems are not adequately resolved, it would be a real “show-stopper” for the AGW theory.

  22. ClimateDemon, your objections at 1173 were not convincing. When one attempts to overturn a large area of scientific knowledge, they should have extraordinary evidence.

    It seems you are making the argument that water vapor can be injected into the atmosphere and serve as a forcing instead of feedback. If that was the case, it would not get us off the hook with fossil fuels since the problem resides with the general relation:

    CH+O2 ==> CO2+H2O

    Combining hydrogen from the crust with atmospheric oxygen to create additional water hardly seems like a good idea under your scenario.

  23. @Philippe Chantreau 1220

    Talk about self-righteousness indignation.

    Actually there is a university course on GCM.

    And MBA programs use case studies extensively. I earned mine before Amazon but I suspect Amazon is a case study(s) in most current MBA programs.

  24. ClimateDemon, your claim in comment 1173 that "The only model that predicts AGW and the CO2 control knob is the one used by Lacis et. al. 2010" is incorrect. The Lacis model and paper describing experiments with it are merely the most explicit and easily understood (at the time) explanations of specifically that particular point. Please see also, just for example, a video of an NAS lecture by Richard Alley, or of his longer AGU lecture.

  25. Deplore_This: How is it that you cannot see the contradiction of you simultaneously complaining that there are no university courses on climate modeling, and pointing to exactly such available courses? Everybody knows there are courses on climate modeling. What people have been telling you, over and over, is that the vast majority of university teaching of climate modeling is done in courses that are not explicitly and specifically titled "climate modeling."

  26. @Tom Dayton 1225

    If you look at my original post at 1162 you will see that was the only course I found and it is not currently offered. I was asking for recommendations for a similar course at another university and I haven’t received any recommendation from this group.

  27. Deplore_This: Another example of you writing your own contradictions of yourself, is your statement "And MBA programs use case studies extensively. I earned mine before Amazon but I suspect Amazon is a case study(s) in most current MBA programs." Exactly! One case study within courses that use other case studies as well--courses that address broader topics than any one of those case studies, or narrower topics than any of those case studies. Few if any entire courses devoted to, and titled, "how to make an Amazon-like mega company." Which was exactly Philippe Chantreau's point. GCMs, and "climate models" more generally, are covered in most atmospheric science courses, to some degree. Portions of those models are covered exhaustively, and not just as case studies, in many courses that are devoted to those portions of theory and modeling such as courses devoted to radiative transfer.

  28. @Tom Dayton 1227

    You’re speculating. Amazon offers a number of excellent business cases.  In any event, Amaxon is a bad analogy to GCM.

  29. ClimateDemon, allow me to make an introduction:

    Nature has been trying for millenia to push more and more water vapour into the atmosphere, through a process called evaporation. Maybe you have met. The amount of water vapour that is added each year is huuuge.

    Unfortunately, the atmosphere has a nasty habit of condensing that water vapour back to liquid (or freezing to solid) and letting it drop out of the sky as precipitation. It's really, really hard to get it to stay there for anything more than a few days. You can get the atmosphere to hold more if you heat the air up, but that means you need something other than water vapour to force that temperature rise.

    Maybe CO2 would work. I wonder. Maybe someone should look into that.

  30. There really aren't any "climate" models. There are models of earth systems, some being "just" atmosphere, some being "just" ocean, some being "just" biosphere, some being "just" land, and so on. Each of those models has sub-models that can and are created and used outside of those bigger models. Any or all of the above models can be combined into really big models that are attempts to model everything.

    Any of those models--the big ones all the way down to the little ones--can be used to research climate, by running them over climate-scale simulated durations. They can instead be used to research weather by running them over weather-scale simulated durations. Indeed, "climate models" essentially are identical to "weather models." Of course there are important differences, but many of those differences are in how the models are set up and run rather than in the hearts of the models themselves. In particular, climate models are initiallized by running them for a few hundred simulated years until they stabilize, which means until weather cancels itself out, so that boundary conditions dominate intial conditions. Another notable example is that weather models rarely get run with and without injections of greenhouse gases, because changes in greenhouse gas emissions are too small to matter on the time scales of typical uses of weather models.

  31. @Tom Dayton 1230

    Alright, I’ll simplify this. How to I evaluate the following claim without relying on someone else’s opinion? (I’ve already read the IPCC reports).

    “There is growing evidence that climate models are running too hot and that climate sensitivity to carbon dioxide is at the lower end of the range provided by the IPCC. Nevertheless, these lower values of climate sensitivity are not accounted for in IPCC climate model projections of temperature at the end of the 21st century or in estimates of the impact on temperatures of reducing carbon dioxide emissions.”
    -— Judith Curry, the former Chair of the School of Earth and Atmospheric Sciences at my alma mater

  32. Deplore_This: It is impossible for you, or anyone else, to evaluate that statement "without relying on someone else's opinion." Because science is a collaborative enterprise. Even, and 100% of, the scientists who create GCMs rely on other people's opinions--critically so. Certainly you can reduce your reliance on someone else's opinion, by learning about climate science. Computer simulated GCMs are only a tiny portion of that climate science. And trying to learn climate science by directly trying to learn computer simulated GCMs is an utterly doomed approach. Several people have given you multiple resources for learning enough climate science for you to start to be able to rely less on other people's opinions. You could stop rejecting those suggestions out of hand.

    With regard to the particular claim you mentioned, you could start with the "How sensitive is our climate?" post here on SkS. Read the Basic tabbed pane first, then the Intermediate, then the Advanced. To dig in a bit more, go to RealClimate and type "sensitivity" into the Search box at the top right, then peruse the resulting posts. If you want to jump to cutting edge research on that topic, see the recent RealClimate post about the CMIP6 models.

  33. @Tom Dayton 1232

    You’re speculating. You may not be able to “evaluate that claim without someone else’s opinion” but that doesn’t mean someone more capable isn’t able to. And for climate research to be science it must promote hypothesis that can be empirically tested. If scientists are not allowed to challenge the common body of opinion like those I posted in 1193 and 1194 then it is not science, it’s group think.

    You don’t need to respond here. I am going to post this philosophical argument under the correct category of SkS. I’ll post a link here.


    [DB] Inflammatory snipped.

  34. Deplore_This: Also, you seem to be overweighting the practical importance of the exact value of sensitivity. If you're in a car 200 feet from a rock wall, heading directly toward that wall, it doesn't really matter much if your speed is 50 or 60 miles per hour; the consequences are bad enough in either case that you should be applying the brakes right now. For climate change there is the additional urgency that the problem gets worse as time goes on, so even if sensitivity is on the low end, that merely delays the same bad consequences by an inconsequentially few years. Yet another time urgency comes from the fact that the primary causes (in particular greenhouse gas emissions) and feedbacks (e.g., lower albedo from loss of ice) are impossible to reverse on time scales that will be useful. Ice loss, for example, effectively is permanent on human timescales. Another problem with delaying action is that warming accelerates due to feedbacks, sort of like interest accruing on a loan. The longer you wait to pay, the more money you need to pay.

  35. @Tom Dayton 1232

    BTW I've already been through the climate sensitivity part of SkS.

  36. @Tom Dayton 1234

    Climate sensitivity is absolutely critical to accurately scientifically predict ACC as are the natural causes of CC. Regulatory policy decisions are based on those predictions. But that is a discussion for another article in SkS.


    [DB] Off-topic snipped.

  37. Deplore_This:

    It is not enough to read the IPCC or any other material. You also have to understand it. I have seen nothing in your postings here to suggest that you understand anything at all about climatology or climate models.

    I have see nothing to suggest that you have understood any of the material that you have been pointed to here, or that you understand any of the materail that you have cut and pasted from denial blogs and sources.

    You parrot stuff you don't understand. You accept everything that suits your pre-conceived bias. You reject everything that disagrees with that bias.


  38. @Bob Lowlaw  1237

    You aren't intelligent enough to understand what I know.


    [DB]  Please note that posting comments here at SkS is a privilege, not a right.  This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Moderating this site is a tiresome chore, particularly when commentators repeatedly submit offensive personal attacks, off-topic posts or intentionally misleading comments and graphics or simply make things up. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.
    Finally, please understand that moderation policies are not open for discussion.  If you find yourself incapable of abiding by these common set of rules that everyone else observes, then a change of venues is in the offing.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter, as no further warnings shall be given.

    Egregious personal attack removed.

  39. Deplore_This , 

    Firstly, allow me to thank you for bringing entertainment to this thread.

    Secondly, allow me to state the obvious ~ being what all readers here are thinking ( including you yourself! ).    It is obvious that part of your activity is you indulging yourself in some trolling (but please be calm, because my words are charitable ~ since the alternative diagnosis would be distinctly more unflattering.)

    But I see that you are actually here for two purposes (whether you realize it or not).    For like many people who start off as climate-science deniers and visit SkS, your mind is split in two.   One part knows that it is in the wrong about the science.  And actually would like to learn "climate".   The other part angrily rejects that self-acknowledgement, and wishes to challenge (and troll) the mainstream science position.   [ Here, I won't now go into your subconscious motivations for rejection of the well-established science ~ but you really do owe it to yourself to do some self-examination.  It is sad for anyone to live the "unexamined" life. ]

    One part of your mind knows that it really ought to learn about such important science.  And because in the long run, the science always wins (and history condemns the foolishness of the Flat-Earthers, Geo-centrists, Anti-Evolutionists, et alia.)

    The other part of your mind (call it the Denialist part) wishes to fight on, and cause as many waves as possible.   Inevitably, this ends up with you embarrassing yourself publicly ~ but the Denialist part is too angry to care about that, and rather enjoys making futile waves.

    Ah, we humans are an interesting lot

    . . . often Deplorable, yet always Interesting.

  40. Philippe Chantreau @1222

    I am not trying to overturn anything.  I just want to see the science done correctly.  Also, your comment about me arguing that water vapor can serve as a forcing instead of a feedback shows that you are still thinking in terms of the "control knob" model which I have already shown in 1173 and 1190 to be false.


    [DB] Making things up is unhelpful.

    Sloganeering snipped.

  41. ClimateDemon @1240,

    You cite your comments @1173 & @1190 as providing demonstration that the CO2 'control knob' concept of climate is "false".

    I would suggest there is no such provided demnstration.

    It takes little effort to examine these comments of yours.

    @1173 you compare the role of CO2 and H2O when accounting for the energy balance of the atmosphere and jump to the assertion that "there is nothing to indicate that CO2 has any 'control knob' effect." Appended to that rather incomplete analysis, you cite Lacis et al (2010) as describing "the only model that predicts AGW and the CO2 control knob" but that Lacis et al are wrong because  this "only model" simplifies the climate system too much. In particular, you describe this "only model" using the Clausius-Clapeyron equation and with "the earth's temperature is represented by a single scalar value T." Your final assertion sets out "It took several false assumptions to make the control knob argument, so there are very likely problems with it."

    @1190 you call for people "who claim that I am making evidenceless assertions" to provide "just one example of such an assertion" that you have made. You append to this call three ground rules which you insist all will agree. (i) A world witout a "uniform" surface temperature is not in "thermal equilibruim". (ii) Use of the Clausius-Clapeyron equation cannot be extended to include the large global temperature variations. (iii) An equation should not be used beyond its limits.

    (ClimateDemon, do correct me if I misrepresent the intention of your comments @1173 & @1190.)

    I find these comments disturbing in many ways but let me here provide a little more than "just one example" of "evidenceless assertions" by naming that "only model."

    That "only model" @1173 can only be the one used by Lacis et al (2010) and that is GISS ModleE which nobody in their right mind could ever describe as being:-

    "a highly oversimplified, zero dimensional model in which the earth's temperature is represented by a single scalar value T, and the H2O vapor concentration is determined by the Clausius-Clapeyron equation at temperature T. This means that the entire globe is rigidly held to this one fixed value of temperature and corresponding value of humidity, which we know is false."

    Yet that is what I read @1173.

    Further, the initial consideration @1173, that CO2 and H2O are treated identically within energy balance equations and that of the two H2O is the more powerful GHG, ignores the obvious point that GISS ModelE models the hydrological cycle (thus setting H2O as a feedback) while the levels of those non-condensing GHGs (of which CO2 is the major component) are simple inputs into the model (thus setting CO2 as the primary GHG forcing agent). And that treatment of CO2 & H2O is the same as that in other GCMs. GISS ModelE is/was never "the only model that predicts AGW and the CO2 control knob."

  42. Bob Loblaw @ 1229

    Well how about that! I, too, have a friend whom I would like you to meet — nonequilibrium. At least I believe you are still strangers since you don’t seem to recognize him at all.

    Yes, H2O vapor will condense if cooled, but not the entire earth instantaneously. However, if you use a single-temperature earth model constrained to thermal equilibrium at all times (ie. CO2 control knob model), this is exactly what you are assuming. By not handling these atmospheric problems regarding the atmosphere as the nonequilibrium system that it is, you miss all transient effects and temperature changes seem to happen quite suddenly. Here are a couple of quotes from the SkS Climate Myth 36 page that I believe illustrate my point quite well.

    Eclectic @268 Climate Myth 36

    … Now picture all CO2 suddenly removed from the atmosphere — result: a strong rapid negative feedback. Temperatures plummet, with widespread snow & frost precipitation on land and a fast-spreading layer of ice on the sea [with further sunlight reflection and further spread of sea-ice, to 100% coverage]. Ultimate result: a frozen world (and with minimal H2O in the atmosphere).

    KR @284 Climate Myth 36

    Non-condensible gases set the thermal equilibrium, condensible gases (water vapor) can only act as feedback because they respond so quickly to a temperature change, even if their overall effect is quite large .

    Do the temperature changes and precipitation actually happen that fast? – Not really. What we are seeing here is an artificial discontinuity in temperature due to the neglect of transient effects in the equilibrium model. It’s somewhat like turning on a new refrigerator and expecting the temperature inside to immediately drop to the operating temperature.

    At this point, I would strongly suggest that you and your AGW comrades educate yourselves some more on the fundamental physical laws behind the climate models, and recognize when you are working with equilibrium and nonequilibrium systems. Maybe then you won’t be quite so bamboozled by CO2 control knobs and icebound earths.


    BTW — I'm actually all grown up now so you can knock off the kid talk!


    [DB]  Inflammatory baiting and sloganeering snipped.  You need to up your game by citing credible sources to support your claims.  Assertions are not sources.

  43. ClimateDemon ,

    your posts here have been rather off-topic for this thread.

    Why not return to the comments section of Climate Myth 36 , where in 2016/2017  you were given frequent & extensive explanations on the subject of H2O vapor and non-condensable GHG's role as climate Control Knob.

    That would be the place for you to express any new & convincing arguments which you may have managed to produce since then.


    [TD] Uh oh, good memory, Eclectic! Perhaps ClimateDemon is yet another sock puppet of JeffDylan, MartianSky, cosmoswarrior, and so on?

  44. Among the bazillion courses that cover climate modeling (sinisterly hidden so they can be discovered only by searching the intertubes for climate modeling course class university!) is this free one by David Archer that starts today. Obviously Deplore_This will deny it is relevant to climate modeling, but other folks might be interested: Global Warming II: Create Your Own Models in Python.

    This class provides a series of Python programming exercises intended to explore the use of numerical modeling in the Earth system and climate sciences. The scientific background for these models is presented in a companion class, Global Warming I: The Science and Modeling of Climate Change. This class assumes that you are new to Python programming (and this is indeed a great way to learn Python!), but that you will be able to pick up an elementary knowledge of Python syntax from another class or from on-line tutorials.

  45. Although water vapour's role may be better discussed elsewhere, ClimateDemon has made some rather inaacurate claims about climate models. That makes this on topic (I think) for this thread.

    Rather than creating a strawman using a simple "single-temperature earth model constrained to thermal equilibrium at all times" (which sounds like ClimateDemon is thinking about zero-dimensional equilibrium models only), let's discuss how precipitation and evaporation work in something like a General Circulation Model (GCM). Such models have full hydrological cycles, and atmospheric dynamics very much like a weather forecasting model. In such a model:

    • Evaporation from the surface (land or water) is calculated as a function of surface moisture availabilty, energy availability, atmospheric humidity, and the atmospheric motions that can move vapour away from the surface.
    • Moist air is then moved around until it cools enough for clouds to form, and they grow until droplets (or ice particles) are large enough to fall to the surface - precipitation.
    • Cooling the air enough to create large amounts of precipitation is usually accomplished by moving the air up, where it cools adiabatically.

    Now, the real world does the same thing, and there are typically three primary ways of getting air to rise and cool. This is covered in pretty much any reasonable introductory weather or climate course or book. The precipitation types related to these processes are used to label the precipitation type;

    1. Frontal precipitation, where warm moist air is pushed upwards by colder (more dense) air. Happens in your typical storms.
    2. Orographic precipitation, where warm air is forced up over hills or mountains. West coasts, monsoons, etc.
    3. Convective precipitation, where air is heated enough to rise on its own. Summer afternoon showers and thunderstorms.

    GCMS include all three of those processes.

    Now, ClimateDemon has said "Yes, H2O vapor will condense if cooled, but not the entire earth instantaneously. ", so we need to consider how long we are talking about. So, what amount of time are we talking about for each of those three processes? What is the time lag?

    • In frontal precipitation, these storms form and dissipate over spans of days. Water does not evaporate and linger in the atmosphere for years, decades, or centuries. We can easily see this in the difference between summer and winter. We also see if in things like hurricanes, that start to lose strength mere hours after they move over land and lose their source of water vapour (energy to feed the storm).
    • In orographic precipitation, you need an upwind source of water, so this is usually found where mountains or high land is close to large bodies of water. The rain dumped on Vancouver (Canada or US - take your pick) is probably only a few hours away from the ocean.
    • In convective precipitation, the clouds form in a few hours after the sun rises (the source of energy for evaporation). The precipitation is predominantly later in the day. It is rare for such events to span continuously over several days, let alone years or centuries. Each day is a new day, with new evaporation.

    So, in both climate models (GCMs) and the real world, removal of precipitation from the atmosphere is a very rapid process. Not instantaneous in the life of a fruit fly, but pretty close to instantaneous in terms of geologic time.

    Mother Nature is unable to drive atmospheric moisture levels up enough to increase the water vapour greenhouse effect for any length of time beyond a few days, because Mother Nature is so good at removing it through precipitation.

    The only way to increase long-term global average humidity is to find some other way to warm the global average atmosphere. A way that has more permanance. Then water vapour can increase, and its greenhouse gas properties will act as a feedback on temperature, but it can't do it on its own.

    Water vapour will not drive climate change. The models agree with reality on this one.

  46. Tom Dayton @1224 and 1244

    Thanks for your responses, and please understand that I am not trying to tear down the general integrity or accuracy of the current models.  I do have serious concerns, however, as to how the climate science community is applying these models to conclude that humans are well on the way to toasting the entire earth with their CO2 emissions.  Over the last 5-10 years, however, the only analysis I have been able to find that at least indirectly blames humans for the warming trend during the last two decades of the 20th century is the CO2 control-knob theory as explained on the Lacis et. al. paper.  I did find several different authors, including John Cook, but they all said pretty much the same thing.

    Now, in your statement 1224, you claimed that this was not the only model and paper that predicts the CO2 control knob and AGW.  So, what I need to know is what models and papers are out there that do predict AGW, and specifically who or what the AGW community (including politicians as well as scientist) is referring to when they make swooping claims such as "scientists say that humans are causing global warming".

  47. Bob Loblaw @2445

    Very good!  Now explain how all of this implies that humans are causing global warming.

  48. ClimateDemon, I gave you links to Richard Alley's lectures. There are relevant posts here on SkS as well, which you were given links to, in moderator's comments. There is no point in me or anyone else responding to your requests for information when you refuse to read or watch those resources. It is clear you are merely trolling.

  49. ClimateDemon @ 1247:

    Sure. I'll do that as soon as you explain what caused the financial crisis of 2008, and give a detailed explanation of the factors leading up to the Second World War.

    What's that? Oh, you mean we're not just playing a game of "ask irrelevant questions?".

    I'll take it as a given that you actually have no constructive argument for your previous statements about water vapour.

  50. Tom Dayton @1248

    What makes you think I haven't looked at those sources and a whole lot more.  If they are so relevant, then howcome they don't even pretend to answer my questions.  And no, I am not trolling but it's getting tempting since asking politely isn't working.

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