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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 1151 to 1200 out of 1297:

  1. @MA Rodger 1141
    You state: “The constant 0.5 imbalance is "almost" (Christy also says "much more" which is a poor description - "more" yes, "much more" no.) the same size as the occasional fluctuations, his examples being monthly wobbles of +/-1.0 & +/-1.5.”
    But Christy’s examples, which you appear to accept, take for instance evaporation of 24 average increasing to compared to 27 over a monthly which is actually a 12.5% change in the amount of heat lost through evaporation. That is clearly not small and that is just a monthly rather than annual, let alone centennial fluctuation of one of the many variables of both inputs (eg amount of solar radiation) and outputs.
    Christy’s diagram does NOT imply 0.5 units is retained. His diagrams show in=out.
    I think Christy believes one possible reason for the difference is explained by the extra heat being lost in the troposphere. This backed up by Steven C Sherwood and Nidhi Nishant “ tropospheric warming does not reach quite as high in the tropics and subtropics as predicted in typical models”.

  2. Rupisnark @1151 ,

    how does evaporation qualify as an input or output of the planet?

    "Top Of Atmosphere" [TOA] is normally taken as the planetary boundary, concerning the gaining of heat/energy and the losing of heat/energy (i.e. concerning the equilibrium or disequilibrium of energy flux re global warming or cooling).   Evaporation & condensation move the heat around within the boundary ~ this plus convections of ocean and atmosphere do variably affect the distribution of heat/energy . . . but this is all part of the "averaging" which contributes to the TOA energy flux.

    The multi-decadal average is the determinant of climate change.  Dr Christy is obfuscating.

  3. rupisnark @1151,
    The basic message is as Eclectic @1152 says, Christy is trying to pull the wool over your eyes. It may be he has managed to pull the wool over his own eyes as well. That would square with him being in denial over climate change.
    And Eclectic @1152 is correct to say that AGW is a phenomenon at the TOA but Christy is not discussing TOA. He is indeed obfuscating.

    Your first point, that global evaporation can vary by large amounts month-to-month (Christy quoted examples of 24 and 27 'units' in his talk, a variation peak-to-peak of some 12%, a little more variation than his words in GWPF Note 17 - "In other words, evaporation might be 24 one month, but it might be 26 the next."), looking at actual monthly variation, the maximum variation of measured global monthly precipitation over decads (there's a graph of it 1980-2011 on this web-page) is about 12% peak-to-peak. Thus to say such a variation could occur "one month" to "the next" is pure exaggeration. The typical variation month-to-month is far far smaller.
    And it is far far smaller doubly-so. Your point that 12% is a big value is twice incorrect. As they say '100% of naff-all is still naff-all.' And the typical variation month-to-month in surface heat flux due to precipitation is naff-all relative to the total precipitation which in turn is a small component of the total surface heat flux.
    And your inference that such variation in precipitation would be even larger at longer timescales, "annual, let alone centennial fluctuation" is not correct. Over longer timescales the variations will tend to average out, although there will be trends caused by the likes of AGW.
    You also suggest that longer term fluctuation could exist in "the many other variables of both inut (eg amount of solar radiation) and output." The solar cycle resilts in TSI wobbling by 1Wm^-2 peak-to-peak. In Christy-units that would be 0.07 units peak-to-peak (of the 11-year cycle) but when averaged out over longer periods the measure would be far far smaller. That this is a minor effect climate-wise is evinced by the absence of any noticable 11-year climate cycle.

    Your second point is that "Christy’s diagram does NOT imply 0.5 units is retained." I don't know why you would suggest such an implication. In GWPF Note 17 Christy states "The extra carbon dioxide we have added to the atmosphere amounts to about an extra 0.5 of a unit of the 100 downwelling from the air." So if the CO2 is there, surely the 0.5 units are there. I see no evidence of any implication that the forcing is not permanent.
    You further suggest that there is "extra heat being lost in the troposphere" which might provide "one possible reason," this proposal "backed up" by an area of the upper troposphere that has not warmed in line with modelled projections. I don't follow the logic. By what mechanism would a cooler part of the upper troposphere constitute a sink for a heat flux of 0.5 Christy-units?

  4. Dr. Christy has a long history of presenting irrelevant, cherry-picked (tiny parts of the Sierras to argue that snowfall isn't decreasing, temps in Alabama which is relatively unchanged relative to other regions of the US), over-averaged (averaging rainfall over the US, ignoring that some regions are changing drier, others changing wetter), unnormalized (temp. extreme records without normalizing for the length of the observations at each station), and/or deceptively graphed data (his temp. record graph, which uses a variety of choices that all exaggerate variability in models/observations while his own look better than they actually are). And yes, I can point to concrete examples of each of those, most directly in the various testimonies he's submitted to Congress.

    It's well worth taking any climate statement from Christy with both a large grain of salt and a careful examination of the evidence presented.

  5. @rupisnark 1151

    Christy's offers his usual distortions that he's been giving for decades. His core argument is that climate models exaggerate bulk tropospheric warming, especially in the topics, and this results from climate models over-estimating climate sensitivity (over-estimating CO2-induced warming). His conclusion is wrong, and the discrepancies he points out are primarily not due to model error, but instead primarily due to errors in inputted forcings for the models, along with internal variability and observational uncertainty (ex: Christy showing tropospheric warming estimates contaminated by stratospheric cooling). So the models aren't greatly over-estimating climate sensitivity.

    If you want an introduction to this subject, then I recommend reading "A response to the “Data or Dogma?” hearing", "Fact sheet for “Causes of differences between model and satellite tropospheric warming rates”", along with the papers with the following DOI numbers: 10.1175/JCLI-D-16-0333.110.1038/NGEO297310.1002/2017GL073798

    Here is a list of some of the problems:

    1) If bulk tropospheric warming was muted relative to surface warming, especially in the tropics, then that would be a sign of a muted negative lapse rate feedback. That would increase climate sensitivity, not decrease it, contrary to what Christy claims. And there's plenty of evidence of a multi-decadal, positive water vapor feedback.
    2) If Christy's position was right, then we'd expect to see a strong model vs. observational analyses discrepancy pre-1999. But we don't. We instead see it post-1999, as one would predict if the issues were with errors in inputted forcings over that period, not over-estimated climate sensitivity.
    3) The models don't greatly exaggerate temperature responses to volcanic eruptions in the way one would expect if Christy were right about over-estimated climate sensitivity.
    4) A number of papers showed that errors in inputted forcings largely explained residual post-1999 differences between surface analyses vs. models; that would also imply a contribution to post-1999 bulk tropospheric discrepancies as well.
    5) Christy has a decades-long history of too hastily jumping to model error as an explanation, when the actual explanation was something else. This includes the notorious case in which he claimed models over-estimated satellite-based bulk tropospheric warming, when actually Christy screwed up the sign of the diurnal drift correction for his UAH satellite-based analysis.

    There are other problems with Christy's position, but I think that list should be enough to get you started.


    [DB] Hot-linked reports and DOI's.

  6. By logic, any model has the potential to be short a certain number of variables.  Yet, without them, it is difficult to grasp functionality of a field of science.

    One of the often missed factors in any scientific study is that we can only assume that what we observe over a long period of time has a consistant variable.  For example, in the early 1970's we observed that polar north migrates at a rate of 7 miles per year towards Russia.  Today, we find that it now is further moving at a rate of 34mpy  (Source:

    It the source provided above, it also provides a model.  Can anyone find something that it's not accounting for?

  7. Worth reading about the subject: latest update at Real Climate. CMIP 3 seems to be doing quite good.

  8. Dr Michael Mann produced his "iconic" hockey stick graph ( model ) while working with the IPCC ,  which showed an exponential increase in global temperatures predicted .Dr Tim Ball publicly stated " Mann belongs in the state pen , instead of Penn State , because his model is a fraud , and his work was paid for by American taxpayers .Mann sued Ball for libel , in the supreme court of Canada ( Ball is Canadian) .Mann refused to show his raw data to the court , after 8 years of proceedings .Mann was charged with contempt of court for this . Ball was awarded all court costs , because  he won the "Truth decision". Why was this climate change "trial of the century not " widely publicized ? It does not fit the government's agenda ! See the entire details at " Principia Scientific" . 


    [PS] Multiple breaches of comments policy

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

  9. Whilst the comment @1158 has been snipped, it may be worth pointing out to the commenter OH YES that the court case for libel by Mann against Ball and co-defendants  'Frontier Centre for Public Policy' resulted in 'Frontier' apologising and settling out-of-court while the action against Ball was terminated by Ball pleading that his aging witnesses who would enable him to argue hs case were dead and dying and that he himself was old and irrelevant and so no damage was caused by him to Mann that could justified the much delayed court action against such a vulnerable defendant. Those in denial over AGW have little difficulty in denying the actual legal situation and so feel they can celebrate the 'dismissal' of the libel action as a victory.

  10. I want to know if the climate models take the latent heat of melting ice into account ? Now the temperature in 80 N area is moderated at 0 C in the summer. (see 80 N graph of DMI) If all ice has gone the temperature will increase very fast. Because it looks like the models are interpolating the observed temperatures , they do not see the latent heat of 334 KJ/kg of melting ice. This amount of energy will be replaced by sensibile heat of water 4,18 KJ/kg.K. Also the specific heat of water is almost twice the specific heat of ice 2.108 kJ/kg.K This also explains why the Arctic Amplification only happens from  October tot April, because it's below zero and thus not part of the fusion water/ice at 0 C. I read in many papers that AA is not well understood. But I'm sure this is the main cause; It's the specific heat of ice in the Arctic compared with specific heat of water in the rest of the world.

  11. Frank:

    Short answer is "yes". It takes energy to melt ice. It takes energy to evaporate water. Freezing and condensation involve the opposite energy conversion. Subllimation (solid-->gas or gas-->solid) is also considered.

    All of this is part of the conservation of energy, which is incorporated into the models.

    Your statement "...because it's below zero and thus not part of the fusion water/ice at 0 C" makes no sense, Perhaps you can clarify.

  12. I am an anthropogenic climate change skeptic because I’ve read criticism of the validity of the climate temperature models referenced by the IPCC. I am not a climate researcher by training or profession and to satisfy my scientific curiosity I’ve been trying to find a university course in climate temperature modeling including CO2 sensitivity analysis. From my undergraduate degree I have an extensive background in operations research, mathematics, computer science and basic physics and chemistry courses for Engineers. So I can’t imagine there is any computer modelling that will be beyond my ability.

    I’ve looked at the undergraduate and graduate curriculum for the top US environmental science universities and have found only one course on climate modeling. Penn State offered METEO 523 in Spring 2020 and only 6 of 30 seats were filled and the course has been since dropped.

    Can anyone suggest a climate modeling course I can pursue? Sorry to ask here but I’ve spent a lot of time searching and have come up short.

    Thank you.

  13. Deplore_This: I don't understand how you could have trouble finding courses. David Archer at U. of Chicago has an online course that starts today. It was the fourth result from my Duck Duck Go search for climate modeling course class online.

  14. Deplore_This, also from that simple search of the internet I quickly found a course at the U. of Washington, Swedish e-Science Education (taught in English), several by MIT, University of California Santa Cruz...

  15. Deplore_This, you could also simply search the internet for climate modelling textbook, and you'll get a plethora of books.

  16. Deplore_This: Not exactly sure what you mean by "climate temperature models referenced by the IPCC" but I assume you mean the GCMs used by CMIP to predict future climate (of which temperature is but variable that can be extracted). If this is the case, then note that these are the best means we have available to predict future climate, but by themselves say nothing about the validity of anthropogenic climate change. They could be completely wrong do to some fundimental algorithmic error which would affect their ability to infer the future, but say nothing about the accuracy of the physic of anthopogenic climate change.

    The science does depend on other models (but not necessarily computer models), especially the radiative properties of gases and the Radiative Transfer Equations in particular. These have real-world applications and the detailed work was initially done by USAF because laser-guided bombs depend on them.

    There are rather more direct ways of checking validity of science (eg empirical evidence). You can also directly measure the increase in surface irradiation. I rather suspect that you would agree that an increase in surface irradation because sun increased its output would warm the planet. The GHE can do that too.

  17. I would also recommend that read the chapter in the IPCC WG1 report on evaluation of climate models before getting too far into the course. (chp 9 in the latest report).

  18. @Dayton 1163, 1164 and 1165
    @ scaddenp 1166 and 1167

    Thank you for the responses. However, I had previously found and reviewed on my own the course syllabuses for your suggested courses before posting.

    Reading the syllabuses of these courses they include basic discussions of what GCM is but not how to do it. None of these courses give the student the opportunity to construct and run GCM and measure their predictive capability by hindcasting.

    I am candidly stating that I am a skeptic of these models and I’m trying to understand the science. I have been frustrated that everything I find is a consensus opinion on these models but I haven’t found anything that allows me to get under the hood and see how the models work for myself and to evaluate the predictive sensitivity of these models.

    I’m not looking for a book. I’m retired and have the time and the money to pay for the best university course I can take. I have the academic qualifications and professional technical knowledge and experience to dig deep into this. My problem is I haven’t found one. I’ve reviewed the curriculum of the top environmental science university programs and I haven’t found a single course. I am asking for a recommendation.

    Thank you again for your response but I still don’t know where to find a course that achieves my objective. I appreciate any assistance you can provide.

  19. Deplore_This: I strongly suggest you take some courses instead of merely reading the syllabi. if you refuse to do that, thinking you know too much already, then go ahead and skip the courses and dive into an open source model:

  20. Deplore_This: You should use one of the textbooks to inform you as you play with that model.

  21. Deplore_This: Perhaps the ISCA framework is what you want.

  22. Deplore_This: I suspect you incorrectly believe that "climate models" are different from climate theory, which is why you do not want to take any of those courses that are not devoted to what you incorrectly think of as climate models. General Circulation Models (GCMs) are just instantiations of those theories in those courses and textbooks. So by learning those theories you will be learning about what you call "climate models." Please try reading Tamino's "Not Computer Models."

  23. I agree that over the past century, the state-of-the-art of modeling and simulation has grown by leaps and bounds, especially since the development of supercomputers in the 1980s. They have been valuable tools for research and development in general, not just climate science. It should be noted, however, that such models are meant to aid scientists in their understanding of certain phenomenon, possibly identifying causes and even making short-term general predictions. They are NOT meant for government use to generate long-term predictions (which no model can do reliably), and use them as a basis for carbon taxes and regulations.

    In order for a model to accurately predict climate change, it must take into account the dynamics of atmospheric fluid motion, realizing that the atmosphere is not in thermal equilibrium. [If it were in thermal equilibrium, there would be a uniform temperature and humidity over the entire surface with no winds nor storms.] This involves solving the time-dependent equations of mass balance (equation of continuity), momentum balance (Navier-Stokes equation), and energy balance which is what is done in the climate General Circulation Models. This is a set of partial differential equations that are first order in time which are generally solved in time by some type of finite difference method given the initial conditions. Note that the terms "forcings" and "feedbacks" aren't even in the vocabulary. Therefore, if there is H2O vapor in the air, its greenhouse effect is accounted for in the energy balance equation. If there is CO2 in the air, its greenhouse effect is also accounted for in the same energy balance equation. The contributions from the H2O greenhouse warming will, of course, be much greater than those of the CO2 warming, but there is nothing to indicate that CO2 has any "control knob" effect.

    The only model that predicts AGW and the CO2 control knob is the one used by Lacis et. al. 2010, the staff here at SkS, or wherever AGW is preached. This is 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. Furthermore, it assumes (through the Clausius-Clapeyron equation) that H2O in its vapor state and condensed states are in constant thermal equilibrium with each other, which is also false. At this point, AGW advocates generally understand the (invalid) argument as to how CO2 becomes the controlling GHG even though it is much weaker than H2O vapor, so I won't repeat it here. In general, those who preach the doctrine that a non-condensable GHG can only be a “forcing” and a condensable GHG can only be a “feedback” have been duped by the fallacies and self-inconsistencies of this “carbon-in-control” model. Another false manifestation of this model is the frozen earth scenario where all CO2 is eliminated, and as a result, there is no non-condensable GHG in the atmosphere to provide the temperature forcing needed to put H2O vapor, the stronger GHG, in the air. As a result, the entire terrestrial greenhouse effect collapses since there isn’t any of either GHG in the atmosphere, thereby leaving an iceball of an earth behind. Aside from the highly anti-intuitive nature of this prediction, it would be totally impossible to test it.

    So what should we do about this CO2 control-knob theory? Do we say "It's what the science says, so we must accept it since we are scientists.", or do we do some critical thinking and say "It took several false assumptions to make the control knob argument, so there are very likely problems with it."?


    [DB]  As this iteration of this user account is new, please read the Comments Policy linked near each Comment Box.  Pay particular attention to the prohibition against sloganeering and note that assertions made must be accompanied by citations to credible evidence, with the more egregious the claim the higher the Burden Of Proof is upon you, the asserter, to fulfill that burden.  Simply saying "ugh-ugh" is insufficient.  Please compose future comments to better comport with the Comments Policy.

    Sloganeering snipped.

  24. ClimateDemon @1173 ,

    Your "CO2 control knob" ideas fall flat, because you have made the critical mistake of looking at climate models only.

    If you look at the bigger context, and examine the paleological evidence, then it becomes very evident CO2 has exerted a major "control knob" effect on planetary climate.  That is also reinforced by the empirical evidence of modern historical data.

  25. @Dayton 1169, 1170, 1171 and 1172

    Thank you for your response. I have spent considerable time studying climate theory and when it comes to predicting future climate change everything I’ve seen is that they are all based upon AOGCM climate simulation models like those evaluated in the IPCC WG1 report you referenced. I am trying to take it to the next level to actually understand and scrutinize the models themselves.

    Rather than teaching myself with an open-source model and a text book I am looking to enroll in a university course that will “provide instruction on development of climate models and… the use of climate models for understanding the dynamics of the climate system processes and behavior”. This is the description for METEO 523 at Penn State:

    This is the only course I’ve found on the subject and unfortunately this course is no longer offered. So I am asking if anyone on this board has a recommendation of a similar course that I can enroll in.

    Thank you again for your help.

  26. @ ClimateDemon 1173

    Thank you for your response. I have a background in Operations Research developing and using models and simulations for other disciplines. This is partly why the models used for climate change predictions are of interest to me. I see that parts of your comment has been censored but my understanding is that AOGCM climate simulation models are in fact used to generate long-term predictions which in turn are used to justify carbon taxes and regulations. This is why I am challenging the validity of the models.

    I think I’m posting in the correct article which states the science is:
    “While there are uncertainties with climate models, they successfully reproduce the past and have made predictions that have been subsequently confirmed by observations.”

    So I am trying to understand what are these uncertainties as well as how well these models hindcast by acquiring an understanding of and hands on use of these AOGCM. I was looking for a university course that teaches this subject to climate researchers.

    You threw me off course by stating that models that accurately predict climate change are a set of differential equations because I haven’t seen that courses in differential equations or even calculus for that matter are course requirements for degrees in atmospheric sciences. So my questions are how are climate researchers taught to use and evaluate these models? And what course can I take that teaches the models that are used to generate long-term predictions which in turn are used to develop public policy?

    Thank you again for your help.

  27. Climate models are around 0.5 million line of code created by discipline experts for each of the climate processes. Starting from scratch to write your own is somewhat ambitious. Note that they are not statistically based so I am skeptical that a background in stats or operations research would help you much. The background requirement is numerical solution to systems of partial differential equations. No shortage of courses of these.

    I cannot comment on US university or course, but going into serious atmospheric sciences here would be based on undergraduate degree in physics and maths. The numerical solution of systems of partial differential equation is specialist area of mathematics - numerial analysis. Our institute (geology/geophysics) typically has mathematicians, programmers and subject specialists working together on problems of this kind of class.

    I still think predicting the base level of future isnt that hard. If surface irradiation increases, then surface gets warmer. The complicated bit is by how much will feedbacks magnify that effect. (Equilibrium Climate Sensitivity) And yes, predictions of future are based  are done by AOGCMs. However, there are also paleoclimate constraints on climate sensitivity. Too crude compared to models but good enough to cause serious concern. Again, the WG1 report is good place to find the papers on emperical constraints on climate sensitivitiy.

  28. @scaddenp 1177

    Thank you for your response. I don’t know what an AOGCM computer model looks like under the hood which is why I am looking for a university course on them. I have a minor in math, I took differential equations, I’ve taken Physics in Engineering school, I’ve not only written computer code but in my career I’ve project managed the creation of multi-million dollar IT systems. I wasn’t planning on writing a half million lines of code but I haven’t seen anything yet that would make me believe I would be in over my head working with an AOGCM model. But I haven’t been successful finding a way to actually work with one.

    I am somewhat confused by your comment. I would think there would be a plethora of courses on climate modeling otherwise how would all of the climate scientists learn how to construct and evaluate them? We have legions of climate researchers at the EPA, who taught them?

    I understand the paleoclimate approach but I am specifically interested in understanding the more sophisticated AOGCMs, specifically their fidelity on climate sensitivity. I’ve gone through the WG1 report and read the results and conclusions. But there are scientists who disagree with their conclusions. To understand the competing arguments I’m trying to educate myself on the models they are using and how they are used. I thought that taking a university course on the subject would be a good approach but not finding one I am stuck. How do the climate researchers at the EPA get the knowledge of which expert and model to believe? What course would they take?

    Thank you again for your help.

  29. Deplore_This: You are finding few courses because you are looking too narrowly for courses labeled specifically "Climate Modelling." As scaddenp explained, there are many components of GCMs, and they are used also independently from GCMS. Also, GCMS use theories, models, and computer code from multiple sub-disciplines.

    So nearly any course you take in atmospheric science will give you some knowledge about GCMs. If you try to take a course specifically about GCMs, you will need to have that prerequisite knowledge in order to gain the insight you say you want to gain. Just look at the Penn State meteorology course list, for example. In addition to the Modelling the Climate System course you wrote is "no longer offered," are many other courses that include solidly relevant knowledge for climate models. (By the way, universities do not offer all listed courses in every academic period. So that course unlikely is discontinued, because unlikely they would list it at all. It might happen to not be offered right now when you want it.) Just one example is course METEO 520: Geophysical Fluid Dynamics, whose prerequisites are vector calculus and differential equations.

  30. Deplore_This: Your own description of your background makes it sound like you are unlikely to benefit much from a specialized course in climate modeling, due to your lack of the prerequisite knowledge. So again I urge you to take some other courses, or if you really are dead set on diving into specifically GCMs (versus other types of models and theories), then get a textbook. Before you even attempt to write code for a GCM, or even look at the code of a GCM, experiment with the easier to use human-computer interface of the EdGCM project, whose underlying GCM is the actual GISS Model II GCM. If you want to look at the code of that underlying GCM, you can get it here.

  31. Deplore_This: The very first thing you might do is take Module 4: Introduction to General Circulation Models, from the Earth in the Future series.

  32. Deplore_This: Tim Osborn has an excellent web page Climate Models for Teaching.

  33. @Dayton 1179, 1180, 1181 and 1182

    Thank you for your responses. All of the other courses that reference GCM's that I've seen don't give me the opportunity to get under the hood of the models and determine for myself how they work. Your suggested Module 4: Introduction to General Circulation Models How Good are GCM's? is a perfect example. So is Tom Osborn's page. There are explanations but there is no way I can hands on understand the nuances of the models and confirm their observations.

    My objective is to understand the models themselves. I apologize in advance if this sounds rude but I really don't care what your opinion is concerning whether I have the sufficient prerequisites to take a course in this subject. Quite candidly, you're wasting your time trying to steer me in a different direction. I know where I want to go and I'm smart enough to determine if I meet the prerequisites for a particular course and to negotiate any shortfall with the school. My question is very simple, do you know of any course that is comparable to Penn State's METRO-523?

    Thank you again for your help and I apologize if I am being too coarse.

  34. Deplore_This: Clearly you are not actually interested in learning anything.

  35. @Dayton 1184

    That’s not very nice or respectful. I thought this was a scientific community. Please just answer my question; do you know of any course that is comparable to Penn State's METRO-523?

    Thank you.

  36. @Dayton

    It's OK if your answer is "no".  That isn't a problem.  No worries.

  37. Looking at CMIP6, I see about 100 different climate models from 49 modelling groups worldwide. Most of climate science is not building AOGCMs. Vast resources are required just to observe climate. I dont do GCMs but the models I work with and maintain involve people learning on the job not products of university courses. I expect the university to provide us with graduates who have the necessary skill base (physics, coding, numerical analysis) to be able to contribute and learn by getting their hands dirty improving the code or adding new features Models are developed by slow evolution.

    On a side note, as far as I can see EPA doesnt do any climate modelling of the AOGCM. I may be mistaken, but it also doesnt strike me as something that would be part of their brief.

    Most people dont have access to the kind machinery required to run an AOGCM.  You would be better getting the code from an earlier generation of models and starting with running that. You might want to look at the isca framework or an old model E. Tom has also suggested the EDCGM which looks an excellent way to learn how these are put together and get a feel for code. Lots of university resources based on it and fits with your desire to understand the models.

    "But there are scientists who disagree with their conclusions" Want to tell more about these people?  I assume you have investigated whether they have the requisite background to make useful criticism and not just reflecting an ideological bias.

  38. You can find the list of participants in the CMIP6 project here (via the map). CMIP models are what inform IPCC reports.

  39. @scaddenp

    Thank you for your response.  I'll look at the CMIP6 and respond to you.  But for now I have a quick question; When you say "us", what organization are you associated with?

    Thank you.


  40. I have a challenge for those who claim that I am making evidenceless assertions. Give me just one example of such an assertion. If you can, please do so and I will and I will make appropriate corrections. Otherwise, please don’t make such claims against me.

    Also, please keep in mind the fact that there are a few items upon which we must be in agreement, or there is no point in attempting to communicate.

    (1) The earth and its atmosphere are not in thermal equilibrium. This is well evidenced by the fact that temperature varies widely over the surface. If the globe were in thermal equilibrium, the surface temperature would be uniform.

    (2) The Clausius-Clapeyron equation is derived for determining the vapor pressure of a substance that is isolated and in thermal equilibrium with its condensed phase. While this equation may be useful in predicting local precipitation over ranges in which there is little temperature change, it is not applicable to global models or effects over which temperatures can vary by 50-60 degrees C.

    (3) We only use mathematical theorems or formulas within the range of their validity. This means we don’t apply the Pythagorean theorem to obtain the longest side of a non-right triangle. Similarly, we don’t use classical equations of motion to predict the motion of a particle traveling at or near the speed of light. Finally, we do not apply the Clausius-Clapeyron equation to the earth and atmosphere system for predicting global effects.

  41. ClimateDemon @1190 ,

    You have made the mistake of promoting "binary" assertions ~ all-or-nothing, black-or-white.  Not "evidenceless"  assertions ~ but illogical assertions.  Illogical, because not sufficiently evidential  i.e. you have chosen to cherry-pick one small area which pleases you, and you have ignored the bigger context that displeases you (and which does not support your assertions).   You have therefore failed to think logically.

    (1)  The globe as a whole is in thermal equilibrium (or very close to it) over duration of time.  Obviously the globe is warming gradually, as evidenced by melting ice and rising sea level.  Surface temperature varies : and the seasonal and historical evidence is that this variation has tight bounds.

    (2)  The Clausius-Clapeyron equation describes physical activities ~ at any local terrestrial site, of varying temperature humidity and pressure.  Obviously these activities operate within bounds, and so can be said to be in a form of equilibrium dynamically within these limits and durations.

    (3)  Because of the above, the C-C equation does apply "to the earth and atmosphere system for predicting global effects"  ~ which have been observed and measured in recent decades.

    ( If my memory serves me, you have fruitlessly questioned these concepts, in other threads in past years. )

  42. Deplore_This:

    I am still unsure as to exactly what you expect to accomplish with respect to climate models. So far, it looks like you have a pre-conception that something must be wrong, and you are on a search for details to support that position. I think you may experience a bad case of confirmation bias, if your postings here are an indication.

    As has been pointed out, climate General Circulation Models (GCMs) are only a small part of climate science. I suggest that you read Spencer Weart's "The Discovery of Global Warming" to learn more about climate science in general.

    In addition, you seem to be under the impression that GCMs represent a "single" climate model. They do not. A GCM is a collection of many types of climate-related models that are knit together to provide a comprehensive view of climate - much as the science of climatology has many, many areas of specialization that need to be knit togther to form a  full picture. Areas that represent distinct sub-classes of "climate" models include (but are not limited to):

    • radiation transfer. Much detailed work was done in the 1960s, when the military wanted to make sure that their IR-seeking missiles would hit the intended targets. (HInt: their "target" was not "climate")
    • atmospheric dynamics (motions). Especially important for weather forecasting. The general field is "Geophysical Fluid Dynamics" (GFD) and atmospheric motion is only one area of application. The same science is used to model air flow on airplane wings, or fluids in pipes or in-ground oil reservoirs, etc. Each application has its own specific issues, so modelling approaches differ - but there is a lot in common.
    • ocean dynamics. Another application of GFD, Oceans have some different issues from atmospheric motions, though.
    • Surface energy balance issues. Receipt of radiation, partitioning into evapotranspiration, thermal fluxes (to atmosphere, to soil or water). Effects of surface type, vegetation, etc. Often referred to as "microclimate". (This was my area of specialization when I worked in the discipline.)
    • soil heat transfer.
    • cloud physics.
    • and so on.

    And once the climatologists develop their theories, there is the task of finding efficient algorithms to transform the science (usually in some mathematical form) into computer solutions. Generally covered as "Numerical Methods" in the computing science world. Systems of partial differential equations that cah be solved either through finite difference, finite element, or spectral methods. These methods are not unique to "climate science".

    No single university course is going to cover the full level of details of every aspect of climate models - or climatology in general. Different groups that develop GCMs make different decisions on which components of which "climate" sub-models will be incorporated, and how they want to code numerical solutions.

    These difference approaches lead to different results in detail, but the broad picture is the same: CO2 from fossl fuels plays an important role in current temperature trends.

  43. @scaddenp 1187

    Thank you for your response. To answer your question here this is an example of scientists who disagree with the IPCC’s conclusion on GCMs:

    “GCMs are important tools for understanding the climate system. However, there are broad concerns about their reliability:

    • GCM predictions of the impact of increasing carbon dioxide on climate cannot be rigorously evaluated on timescales of the order of a century.
    • There has been insufficient exploration of GCM uncertainties.
    • There are an extremely large number of unconstrained choices in terms of selecting model parameters and parameterisations.
    • There has been a lack of formal model verification and validation, which is the norm for engineering and regulatory science.
    • GCMs are evaluated against the same observations used for model tuning.
    • There are concerns about a fundamental lack of predictability in a complex nonlinear system.

    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. The IPCC climate model projections focus on the response of the climate to different scenarios
    of emissions. The 21st century climate model projections do not include:

    • a range of scenarios for volcanic eruptions (the models assume that the volcanic activity will be comparable to the 20th century, which had much lower volcanic activity than the 19th century
    • a possible scenario of solar cooling, analogous to the solar minimum being predicted by Russian scientists
    • the possibility that climate sensitivity is a factor of two lower than that simulated by most climate models
    • realistic simulations of the phasing and amplitude of decadal- to century-scale natural internal variability

    The climate modelling community has been focused on the response of the climate to increased human caused emissions, and the policy community accepts (either explicitly or implicitly) the results of the 21st century GCM simulations as actual predictions. Hence we don’t have a good understanding of the relative climate impacts of the above or their potential impacts on the evolution of the 21st century climate.”
    -— Judith Curry, the former Chair of the School of Earth and Atmospheric Sciences at my alma mater

  44. @scaddenp 1187

    Here is another example of scientists who disagree with the IPCC’s conclusion on GCMs where more than 500 scientists and professionals in climate and related fields sent a “European Climate Declaration” to the Secretary-General of the United Nations asking for a “long-overdue, high-level, open debate on climate change” and were denyed.

    “There is no climate emergency…Climate science should be less political, while climate policies should be more scientific. Scientists should openly address the uncertainties and exaggerations in their predictions of global warming, while politicians should dispassionately count the real benefits as well as the imagined costs of adaptation to global warming, and the real costs as well as the imagined benefits of mitigation.”

    “Natural as well as anthropogenic factors cause warming. The geological archive reveals that Earth’s climate has varied as long as the planet has existed, with natural cold and warm phases. The Little Ice Age ended as recently as 1850. Therefore, it is no surprise that we now are experiencing a period of warming.”

    “Warming is far slower than predicted. 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.”

    “Climate policy relies on inadequate models. Climate models have many shortcomings and are not remotely plausible as policy tools. Moreover, they most likely exaggerate the effect of greenhouse gases such as CO2. In addition, they ignore the fact that enriching the atmosphere with CO2 is beneficial.”

    “There is no statistical evidence that global warming is intensifying hurricanes, floods, droughts and suchlike natural disasters, or making them more frequent.” “However, CO2-mitigation measures are as damaging as they are costly. For instance, wind turbines kill birds and bats, and palm-oil plantations destroy the biodiversity of the rainforests.”

    “We invite you to organize with us a constructive high-level meeting between world-class scientists on both sides of the climate debate early in 2020. The meeting will give effect to the sound and ancient principle no less of sound science than of natural justice that both sides should be fully and fairly heard. Audiatur et altera pars!”

  45. @scaddenp

    As I stated in my first post 1162 I am an anthropogenic climate change skeptic because I’ve read criticism of the validity of the climate temperature models referenced by the IPCC like those posted in 1193 and 1194. The corrupt media and the bureaucrats at the EPA say it’s settled science but I see no record of balanced climate research or any open debate. It appears that scientists who raise doubts of the validity are shunned and unfunded.

    So my dilemma is how do I know what and who to believe. It is my nature not to blindly believe anything, especially what the government tells me. I thought a solution would be to take a university course in climate modelling so that I could hands on use and understand the development of GCMs and form my own opinion. If this was the 16th century and I’d probably get a telescope to test Galileo’s claim of heliocentrism. I am surprised to find that there aren’t such courses which leads to an even more startling revelation that the majority of the “97% of climate experts agree humans are causing global warming” have never been taught or used a GCM themselves and base their opinion on the opinion of others. To me that looks more like group think than science. And they call us climate skeptics “flat earthers”.

    So my dilemma remains and I’m not sure what to do next. I may contact Penn State and see if course material is available from their last course on GCM. I’m not going down the paleological path because there are other issues there and because the IPCC’s opinion that is used for public policy is based on GCM predictions. I remain open to any suggestions. Thank you again for your help.

  46. @Bob Lowlaw 192

    Thank you for your response. As I stated in my first post 1162 and my post at 1195 I am an anthropogenic climate change skeptic because I’ve read criticism of the validity of the climate temperature models referenced by the IPCC like those posted in 1193 and 1194. I am aware that there are multiple climate models and classes of climate models. According to the syllabus the Penn State course I referenced included multiple climate system components including atmosphere, ocean, land, cryosphere, biosphere, role of parameterizations and model coupling.

    Without repeating my post at 1195 I’ll just state here that I remain open to any suggestions. Thank you again for your response.

  47. Deplore_This:

    Judith Curry is not, I repeat, not, a reliable source of information. She peddles "uncertainty", and much of what she says is simply wrong. Start here:

    and continue here:

    In addition, pretty much anything published by the GPWF is full of crap:

    Same for the Climate Intelligence Foundation:

    You need to find better sources of information. You're paying attention to people that are selling shite to you.

  48. @Bob Lowlaw 1197

    As I stated Judith Curry was the Chair of the School of Earth and Atmospheric Sciences at my alma mater. I don’t know her personally but I know people who do and they tell me she is credible. As a courtesy I reviewed your links and I don’t see anything that refutes that opinion. It appears to me that Judith Curry is a scientist who disputes some of the “group think” and is shunned and unfunded. If the climate science community can not engage in open debate then it is not practicing science. As a climate skeptic I am accused of not believing science but without open debate it is not science.

    Bob, I believe Judith Curry before I believe you. So my dilemma remains and I’m not sure what to do next. Thank you for your response.

  49. Deplore_This:

    Who tells you she is "credible"? On what basis are they credible?

    You have chosen who you are going to believe. That is not the sign of a skeptic. You have bought into the shite they are selling to you. There are lots of places on the internet that will point out the crap you have read that is confirming your bias.

    Go read the Spencer Weart link I posted earlier.

    Have you read the IPCC reports, or do you just read the comments about the IPCC that you get from your "credible" sources?

    I agree with Tom Dayton. You are not here to learn anything.

  50. @Bob Lowlaw 1199

    Quit with your sanctimonious crap. It certainly doesn’t reflect well on your scientific reputation. I came here stating that I’m a skeptic and wanted a recommendation for university course on GCM, not to believe one person over another.

    Judith Curry was the Chair of the School of Earth and Atmospheric Sciences at a well-respected technical university and was obviously imminently qualified to get the job. I’m not going to post people’s names on the Internet to satisfy your curiosity.

    I looked at the Spencer Weart link and I’m already beyond that level. I have read the IPCC reports.

    If you were going to scientifically challenge Judith Curry’s opinions that I referenced you would point to published scientific scrutiny and not just make juvenile comments. The more emotional you become the more you add to her credibility in my eyes.


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