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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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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)

At a glance

So, what are computer models? Computer modelling is the simulation and study of complex physical systems using mathematics and computer science. Models can be used to explore the effects of changes to any or all of the system components. Such techniques have a wide range of applications. For example, engineering makes a lot of use of computer models, from aircraft design to dam construction and everything in between. Many aspects of our modern lives depend, one way and another, on computer modelling. If you don't trust computer models but like flying, you might want to think about that.

Computer models can be as simple or as complicated as required. It depends on what part of a system you're looking at and its complexity. A simple model might consist of a few equations on a spreadsheet. Complex models, on the other hand, can run to millions of lines of code. Designing them involves intensive collaboration between multiple specialist scientists, mathematicians and top-end coders working as a team.

Modelling of the planet's climate system dates back to the late 1960s. Climate modelling involves incorporating all the equations that describe the interactions between all the components of our climate system. Climate modelling is especially maths-heavy, requiring phenomenal computer power to run vast numbers of equations at the same time.

Climate models are designed to estimate trends rather than events. For example, a fairly simple climate model can readily tell you it will be colder in winter. However, it can’t tell you what the temperature will be on a specific day – that’s weather forecasting. Weather forecast-models rarely extend to even a fortnight ahead. Big difference. Climate trends deal with things such as temperature or sea-level changes, over multiple decades. Trends are important because they eliminate or 'smooth out' single events that may be extreme but uncommon. In other words, trends tell you which way the system's heading.

All climate models must be tested to find out if they work before they are deployed. That can be done by using the past. We know what happened back then either because we made observations or since evidence is preserved in the geological record. If a model can correctly simulate trends from a starting point somewhere in the past through to the present day, it has passed that test. We can therefore expect it to simulate what might happen in the future. And that's exactly what has happened. From early on, climate models predicted future global warming. Multiple lines of hard physical evidence now confirm the prediction was correct.

Finally, all models, weather or climate, have uncertainties associated with them. This doesn't mean scientists don't know anything - far from it. If you work in science, uncertainty is an everyday word and is to be expected. Sources of uncertainty can be identified, isolated and worked upon. As a consequence, a model's performance improves. In this way, science is a self-correcting process over time. This is quite different from climate science denial, whose practitioners speak confidently and with certainty about something they do not work on day in and day out. They don't need to fully understand the topic, since spreading confusion and doubt is their task.

Climate models are not perfect. Nothing is. But they are phenomenally useful.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

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 shown 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. Sea level rise is a good example (fig. 1).

Fig. 1: 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. A 2019 study led by Zeke Hausfather (Hausfather et al. 2019) 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."

Talking of empirical evidence, you may be surprised to know that huge fossil fuels corporation Exxon's own scientists knew all about climate change, all along. A recent study of their own modelling (Supran et al. 2023 - open access) found it to be just as skillful as that developed within academia (fig. 2). We had a blog-post about this important study around the time of its publication. However, the way the corporate world's PR machine subsequently handled this information left a great deal to be desired, to put it mildly. The paper's damning final paragraph is worthy of part-quotation:

"Here, it has enabled us to conclude with precision that, decades ago, ExxonMobil understood as much about climate change as did academic and government scientists. Our analysis shows that, in private and academic circles since the late 1970s and early 1980s, ExxonMobil scientists:

(i) accurately projected and skillfully modelled global warming due to fossil fuel burning;

(ii) correctly dismissed the possibility of a coming ice age;

(iii) accurately predicted when human-caused global warming would first be detected;

(iv) reasonably estimated how much CO2 would lead to dangerous warming.

Yet, whereas academic and government scientists worked to communicate what they knew to the public, ExxonMobil worked to deny it."

Exxon climate graphics from Supran et al 2023

Fig. 2: Historically observed temperature change (red) and atmospheric carbon dioxide concentration (blue) over time, compared against global warming projections reported by ExxonMobil scientists. (A) “Proprietary” 1982 Exxon-modeled projections. (B) Summary of projections in seven internal company memos and five peer-reviewed publications between 1977 and 2003 (gray lines). (C) A 1977 internally reported graph of the global warming “effect of CO2 on an interglacial scale.” (A) and (B) display averaged historical temperature observations, whereas the historical temperature record in (C) is a smoothed Earth system model simulation of the last 150,000 years. From Supran et al. 2023.

 Updated 30th May 2024 to include Supran et al extract.

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

Last updated on 30 May 2024 by John Mason. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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.

Denial101x videos

Here are related lecture-videos from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Dana Nuccitelli: Principles that models are built on.

Myth Deconstruction

Related resource: Myth Deconstruction as animated GIF

MD Model

Please check the related blog post for background information about this graphics resource.

Fact brief

Click the thumbnail for the concise fact brief version created in collaboration with Gigafact:

fact brief


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Comments 476 to 500 out of 903:

  1. If the temperatures end up outside the range of the models, then that would be interesting. Remember every model run represents a possible future climate given those forcings. I would expect Ar5 to be better absolutely. It will probably reflect ongoing research into the aerosol effect and size of current aerosol forcing.
  2. The models are unreliable because there is an implicit assumption that backradiation from a cooler atmosphere is capable of either (a) warming or (b) slowing the rate of cooling of a (significantly) warmer surface. In a new extension of the work of Einstein and Planck, computations on blackbody radiation have show conclusively that this is a physical impossibility. For any given temperature, a surface emits at a peak frequency (proportional to the absolute temperature) this cut-off frequency being determined by Wien's Displacement Law - see Wikipedia. (There is a maximum a bit above the peak as the distribution is strongly attenuated.) Coherent radiation which the Earth's surface receives and which has frequencies above the maximum (ie SW solar insolation) will all be converted to thermal energy which can be stored and subsequently emitted with the appropriate (lower) IR frequencies, or diffused into the atmosphere or transferred by evaporation. Such transfers by these thermodynamic means reduce the remaining energy available for radiation. This is why the Earth's surface does not act anything like a perfect blackbody. However, radiation which has frequencies significantly below the peak in the emitting spectrum cannot be converted to thermal energy and thus has no effect. It is immediately emitted with the same spectrum and intensity, thus leaving no energy behind. It might as well have been reflected because the end result is similar. This is why frost lying in a shady spot does not get melted all day long by backradiation, even if the ground and air are slightly above freezing point. This is why a gas will not absorb when an emitter is radiating (spontaneously) until that emitter is warmed above the temperature of the receiving surface. (Spectroscopy confirms this.) So it is a fact of physics now proven (and never disproven) that the assumed warming effect of backradiation cannot happen. Thus an atmospheric greenhouse effect assumed as a result of radiative transfer is a physical impossibility. Those who are well read will know of the "Computational Blackbody Radiation" note to which I am referring which was written by a widely published Professor of Applied Mathematics whose name has (predictably) been somewhat slurred due to misinterpretation and lack of understanding. Having had over 45 years experience in Physics I can vouch for the accuracy of his results in such computations which I realise may well be above the heads of many readers here.
  3. Doug Cotton?
  4. That's the first name that came to mind - style is much the same.
  5. What an incoherent blabbermouth..
  6. Doug Cotton @477, the theory you have just proposed is complete nonsense, and in contradiction to inumerable experiments conducted primarily by the USAF to understand the behaviour of IR radiation in order to design effective heat seeking missiles, and FLIR cameras. If you expect us to believe us, you need to refer us to the actual scientific papers explaining the experiments you purport prove your theory, and giving the experimental results. Failing that, we will recognize it for the con it is, and continue to believe that IR lamps will warm a surface, contrary to the theory you have proposed.
  7. However, radiation which has frequencies significantly below the peak in the emitting spectrum cannot be converted to thermal energy and thus has no effect. It is immediately emitted with the same spectrum and intensity, thus leaving no energy behind. It might as well have been reflected because the end result is similar.
    Anyone can go into their kitchen and disprove this canard. Please, Mr Cotton, tell me then how the humble microwave oven is able to heat my dinner. The microwave radiation, according to your obscure physicist's incorrect theory, is incapable of adding energy to my lunch, which naturally emits (dimly) in the longwave infrared band. After exposure to the microwave radiation, my lunch is warmer than it was before, but you say this is not possible... Perhaps microwave manufacturers are all in the worldwide conspiracy?
  8. Tom Curtis & Skywatcher @481 & 482 Regarding gases absorbing, see second paragraph here Regarding frost not melting, anecdotal only here For mathematical proof (which I have studied and agree with and which is not disproved) read Computational Blackbody Radiation. I am only interested in seeing any experiment (eg metal plates receiving backradiation at night) which demonstrates warming. Two identical radiators in open air warming up together will not help each other to warm faster because neither is hotter than the other. If they did you'd have energy creation. When the Earth surface and the first 1mm of the atmosphere are very close in temperature S-B law says there would be very little radiation. Microwaves (and lasers) are red herrings - they are not emitting spontaneous blackbody radiation - which is the subject above. Microwaves are a very special form of waves anyway which mostly only warm things like fat and water molecules up to boiling point only. They are irrelevant regarding backradiation.
  9. Doug Cotton @483, scientists are interested in theories which are wrong in interesting ways, ie, wrong in such a way that you learn something new in trying to refute it. Claes Johnson is wrong in that boring old way of just being absurd. He purports to derive a new theory of black body radiation which differs significantly from Planck's Law and the Stefan-Boltzmann Law, both of which are fundamental to the theory of radiation and have been multiply confirmed by observation. In place of these he offers a theory with no experimental confirmation, which we no will be disconfirmed experimentally because its predictions differ from those of a theory which is well confirmed experimentally; and whose only intellectual virtue is that it would refute a common misunderstanding of the greenhouse effect. That is not an interesting theory. Of course nobody has tried to disprove it, anymore than actual geologists don't waste their time trying to disprove hollow earth theories. I ask you again to link to papers showing experimental confirmation of the theory. Your failure to either do so, or to reject the theory as unempirical nonsense would show you once again to be trolling, and I would ask the moderators to enforce against you the ban for repeating, unmitigated trolling that has led to your prior banning which you are currently violating.
  10. Cotton seems to think objects would be aware, when receiving radiation, the circumstances under which that radiation was emitted, whether blackbody or not. This is desperate, handwaving nonsense to defend a theory which, as Tom says, is not experimentally verified.
  11. skywatcher... the Hermeneutics of Doug's "cut-off frequency being determined by Wien's Displacement theory" is clear. Claes Johnson looked at Wien's displacement law saw the Peak wavelength / frequency described as maximum and interpreted this as a cut-off - although hedged with "heavily attenuated" if you look at his writing. 1/ I can understand how a Swedish native speaker could confuse Maximum in the sense of Peak and in the sense of "the highest value possible". To a mathematical - rather than a physics - the error would be opaque. 2/ the "heavily attenuated" hedge is a bit odd as, as we all know, the distribution of BB radiation falls both above and below the maximum... 3/ none of this actually follows form Prof. Johnsonns conscious-quanta ... which stands alone in it's bizarrness. 4/ Doug does not have the where-withall to either read Prof. Johnsonns material in enough detail to see this nor to understand empirical physics which demonstrate it one way or the other.
  12. Consider for a moment how backradiation is measured (a Pyrgeometer). The thermopile has to be heated by the incoming radiation to generate a voltage at all. According the imaginary 2nd Law postulated by Doug and others, this couldn't happen. And yet a pyrgeometer makes measurements that are completely consistent with what boring textbook versions of thermodynamics postulate. If backradiation cannot warm the surface, then what physics accounts for what a pyrgeometer measures?
  13. Climate-Change-Theory/Doug Cotton - Let's be clear here. Your arguments violate observations and physical laws, and go against even freshman physics. It's just not a viable objection. Please - go read a book or two... such objections are why many 'skeptics' are not taken seriously.
  14. elsa - Redirecting from an off-topic comment on another thread: "They then go on to say "computer models have recently shown that during periods when there is a smaller increase of surface temperatures, warming is occurring elsewhere in the climate system, typically in the deep ocean." To be clear on this, global circulation models incorporating the most accurate physics we have on atmospheric and oceanic circulation under various forcing conditions exhibit behaviors including decade long very low or very steep atmospheric warming, with the inverse generally showing in deep ocean regions. This is entirely consistent with observations of climate behavior under, for example, ENSO extremes (El Nino, La Nina cycles). "That statement, as I pointed out yesterday cannot be true. It is not within the power of a model to do such a thing." And here you would be incorrect.
  15. Having been requested to post my view on models here rather than Facebook am happy to add my four pence worth (-Snip-). The 2011 temperature was below the IPCC projection for no increase in CO2 (after quite a large one) while your own sea level example doesn't seem to be consistent with others either in the past (2003, reported in 2008) or the present (note that you said the projection may have been conservative, but in a truly chaotic system chaotic things happen, in fact they have to as that is its nature) Your articles are only as good as the latest data and can so quickly become out of date, (-Snip-). (-Snip-).

    [DB] Time to acquaint yourself with this site's Comments Policy.  You should be familiar with it:  that of the SkS FB page was modeled on it.

    Multiple violations of the Comments Policy snipped.

  16. I'll add a nice little discussion here following the revelation that on far easier to measure population data the true figure of climate refugees (based on what the models said would happen) in 2010 was zero. You do not use computers to do anything more than play games with role playing software, you do not pretend you can guess the future. That tends to come back and bite you in the tushy.
  17. Climate models have no skill at decadal prediction where internal variability dominates, nor do they pretend to. For study of that internal variability, F&R demonstrate how ENSO, solar and aerosols account for most of variability while the underlying trend follows IPCC predictions. ENSO is hard to predict even months out let alone be part of climate models. You can find a better comparison of model versus data here Sealevel drop is not due to the ice suddenly stopping to melt because of cooler temperatures. Far from it - ice continues to decline. Instead it is due to La nina precipitation change dumping water on land. See here for more discussion and here for GRACE data showing where the water went.
  18. VoR- Did you read the original BBC? First, this is not based on climate models (which are matching predictions just fine), nor is about "climate" refugees. Second estimating whether a person is an environmental refugee is difficult and the number is absolutely not zero. A comparable number would have to come from the same source. "You do not use computers to do anything more than play games with role playing software, you do not pretend you can guess the future" That's sailing very close to the wind on the comments policy here. Please stick to supported facts.
  19. The article also makes claims based a map linked to here An interesting message can be found there now. Sounds like some journalist axe-grinding not science.
  20. I've been busy going through my own archives, someone here has taken the trouble to compare as many predictions from models with the following reality as possible, (-Snip-). But as people have incredibly short memories and attention spans unless recorded nearly everyone's off on a new trip (-Snip-), the more so the greater ahead they are predicted. 2100 would make a perfect one, as when picked by the IPCC no one on earth could fulfil the experiment as they'd have needed to be 110 at the very youngest. (-Snip-)

    [DB] Time to acquaint yourself with this site's Comments Policy.  You should be familiar with it:  that of the SkS FB page was modeled on it.

    Multiple violations of the Comments Policy snipped.

  21. vor. Well here's the very latest data-model comparison for the completed 2011 year at RealClimate. I'm not sure how much effort should be expended on detailed projections for 100+ years. You can just see how much difference arises from using various scenarios. Climate might be difficult, but predicting what people might do and when they might do it is even more so. One question. Were you looking at the 'basic' or the 'intermediate' version of this post. And a quiet word in your shell-like "That's a fine parameter for a scientific experiment, setting the end point beyond observable time, possible a clue as to the general integrity of the whole project?" is as close to an accusation of fraud as dammit is to swearing. Don't be surprised if the moderators give you a hard time.
  22. Adelady#496 vor's objection to use of 2100 as an endpoint is also utterly without meaning. It's arbitrary. And vor provides a good example of the fact that everybody and their dog are checking those predictions at least annually. This is the real issue that vor doesn't want to face: What data do the checkers (and their dogs) use to check the predictions? Is it a carefully cherrypicked few years ('it hasn't warmed since last week!')? Is it just one parameter of particular interest ('it's snowing in Europe!')? Is it just one prediction ('my TV news said there aren't any climate refugees!')? Or is it the entire record (as F&R2011 analyzed, as BEST verified) and the entire spectrum of the evidence (as we see here)?
  23. VoR - let me acquaint you with another way this site works. Your "model predictions are wrong" is list of cherry-picked, long-debunked guff from likes of Tisdale, Watts, CO2"science". This is not how it is done. If you want to contest model/observations, first you reference the published science source that makes the prediction. That takes case of the strawman arguments. Next you reference the published data that refutes it. That way we can see if it fair prediction or just cherry-picking. Also, models are tied to scenarios. Ie "IF the forcings are this, THEN the climate will this". That beats false prediction. Now the models stuff out miles of predictions and some are more robust than others. eg trends in global climate parameters are pretty robust. Regional prediction is less robust especially when it depends on how ENSO will change (if it does) with rising temperature. That is an open question.
  24. vor: "You do not use computers to do anything more than play games with role playing software, you do not pretend you can guess the future. That tends to come back and bite you in the tushy." What the heck is that? Are you saying that any attempt to predict the future is useless? Or are you saying that computer models aren't the best way to predict (if so, you got something better?)? Or are you saying that a specific model has problems, problems which you are able to detail/explain? Or are you saying that one person's prediction about climate refugees casts doubt on the scientific work of thousands? A little clarity, if you don't mind.
  25. Continuing from a comment posted by Manny: Sorry, what is extraordinary about the claims of climate theory? They are fully consistent with everything else we know about physics. The time period for model validation is not some arbitrary no. (eg why stop at 100,000?) but more determined by internal variability which is calculable. However, the basic theory of surface temperature, if correct, must work throughout all times and on all planets. There are two problems going back long periods in time: 1/ computer power - full resolution, 100 year runs take a lot of muscle and time. Its more normal to look at specific parts of past time (eg LGM, ememian peak, YD, PETM etc). You dont gain a lot with very long runs. 2/ Uncertainty as to the inputs increase. ie what was past albedo, atmosphere composition, TSI etc. There are uncertainties in proxy records for those as well as uncertainties in the proxy temperature. You can say that paleoclimate temperature proxies are consistent with climate theory and proxies for climate forcings. Ditto for temperature regimes on other planets. However, paleoclimate isnt the only way to validate model - they after all push out predictions on huge no. of variables on various time scales. See Chpter 8 of that IPCC report. However, the modellers would also I am sure caution you that it is better to consider model skill rather than simple model validation. In considering the implication of the modelling for future planning, this is what matters.

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