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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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Climate Hustle

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.

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 31 December 2016 by pattimer. View Archives

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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 1101 to 1107 out of 1107:

  1. CommonSense @1099,

    I will read your comment less literally than Eclectic @1100.

    The instrument temperature records becomes less extensive the further we run back in time, eventually measuring just Western Europe, Eastern US & a record in India. And then they require the invention of thermometers so there are none before the 1700s. But there are proxy measurements that show us (with the few temperature records) that global temperature was cooler in those times.

    The proxy data on its own allows us to see that it was warm back a few thousand years ago (the Holocene Thermal Maximum) and warmer still 100,000 years ago (the Eemian Thermal Maximum). Before that, to find it hotter still, you have to go back millions of years to the time when North & South America were joining together and there was no Arctic Sea Ice. But one difficulty in a definitive ruling about how hot these periods were relative to today is calibrating those proxy data with instrument data. The evidence is pointing to today being hotter than the Holocene Maximum but not as hot as the Eemian, athough we soon would be if we allow AGW to run its course. And the present warming is sudden relative to the arrival of those earlier warm periods.

    As for the thermal effect of solar panels. The panels must surely absorb more solar energy than the land without the panels. And a portion of that extra heating will replace fossil fuel use. As fossil fuel use results in higher CO2 levels in the atmosphere, that portion of extra heating by the panels results in an annual reduction in warming at least equal to that portion of extra heating. So after 10 years, the CO2 from the fossil fuels would have beeen warming the planet 10x more than the extra heating.

    Mother Nature will surely take care of the planet in the long run. But the mass extinction humanity is generating in the meantime will be very destructive, for humanity as well as for the natural world.

  2. CommonSense @ 1099

    Yes, we often hear things like e g "this year is the hottest year since 1898". But that does not mean that 1898 was hotter. It usually only means that the data set referred to starts at 1898. So the phrase is shorthand for "this year is the hottest year in the entire data set upto this year. And that data set starts in 1898".
    Note to others: And that's a good reason to avoid that ambiguous way of phrasing. Because if you try to interpret it using only your common sense you may get it all wrong.

  3. And where have you 'often' heard, "this year is the hottest year since 1898"?

  4. The pattern "hottest year since VXYZ" is rather usual. As an example we can go to NOAA's web-site for presenting time series for global land and ocean temperature anomalies at You can see that the particular data set presented there is from 1880 upto now. And in this set there are new annual top records lately set in 2014, 2015 and 2016. Those years it was correct to refer to this data and say "this is the hottest year since 1880". And there are of course other data sets, global and regional, so other years are possible.
    I tried to net-search (with Google) for some instances of this pattern. I found:
    "hottest year since 1880" 18900 hits
    "hottest year since 1895" 59 hits
    "hottest year since 1896" 14 hits
    "hottest year since 1900" 51 hits
    "hottest year since 1901" 97 hits
    "hottest year since 1909" 11 hits
    "hottest year since 1910" 28 hits
    But the point is that if I say "2016 was the hottest year since 1880" that could make someone believe that I mean that 1880 was hotter. I most certainly do not mean that. So I avoid that particular wording.

  5. Ignorant Guy @1104,

    You are entirely correct to say that the problem is the use of the phrase "hottest year since X" when what is meant is "hottest year on record" when X is the start-year of that record. Looking at a few of those thousands of Google hits, the phrase usually does not track back to 'responsible' organisations but it seems to be later reporting when journalist-speak for "hottest year on record" & "the record began in X"  is edited down to a shorter phrase.

    There is ClimateChangeNews who use the headline "Earth on course for hottest year since 1880" yet NOAA put it as the likely "new record for the warmest annual average temperature since records began in 1880." Note this NOAA statement is correct. The ClimateChangeNews headline is not correct -1880 was a lot colder than the year they were reporting about  - 2015.

    Mind, the press officers attached to the likes of NOAA or NASA are also journalists and not immune to compressing information into a single but inaccurate statement. Although the article does say "Last year was the third consecutive year in which global temperatures were more than 1.8 degrees Fahrenheit (1 degree Celsius) above late nineteenth-century levels," it also promenantly says "Earth’s global surface temperatures in 2017 ranked as the second warmest since 1880, according to an analysis by NASA."

    But even so, you'd surely have to be a bit of a foolish pedant to run away with the belief that 1880 was as warm or warmer than today's temperatures, even if you inhabited that contrarian planet Wattsupia.

  6. MA Rodger @ 1105

    you'd surely have to be a bit of a foolish pedant to run away with the belief that 1880 was as warm or warmer than today's temperatures

    Yes, I would tend to agree. But I have seen it a lot. And recently.
    Actually I strongly suspect that CommonSense @ 1099 is afflicted by precisely that misunderstanding.

  7. Dana's YouTube graphs are spectacular!

    I've been looking for such model comarisions that show years 2016, 2017, 2018 because most everthing I find is way out of date and shows the models being too high. I'd love to see those graphs directly on this site, since I'd rather use for a reference thanYouTube.

  8. If the models are making predictions of between 1 and 4.5 degrees change per doubling, then they are unreliable. This is a 450% variance. There can only be one answer to how much, if anything, CO2 is contributing to the climate. Why are the models coming up with such different results? Why are they coming up wth multiple answers to the same question?


    [PS] Please dont spam multiple threads. Best to discuss one thing on a thread that you think is important and when satisfied, move to another. (And how do calculate 450% - what is your denominator). Meanwhile, this post from people who do the modelling might be helpful. While models have flaws, they remain the best tool we have for predicting the future - far better than say chicken entrails or assuming tomorrow will be same as today.

  9. Just some food for thought...  These published studies raise plenty of questions about the validity of the the models being used and the accuracy of the historical data being inserted into them.

    The role of historical forcings in simulating the observed Atlantic multidecadal oscillation


    Inability of CMIP5 Models to Simulate Recent Strengthening of the Walker Circulation: Implications for Projections


    [DB] Please be specific and provide a rationale for each of the studies you linked to and why you feel that they support your claims.

  10. Weaknesses with models is hardly news - ask any modeller. what you are looking at is the processes by which models get better. Numerous studies have shown that basically models suck at regional-level prediction for reasons including difficulties with ocean circulation. They are also hopeless at decadal-level prediction. If the models were better, we would have such a wide range on ECS estimates.

    However the models have plenty of skill at many other important variables and are by far the best tools we have for predicting future climate (ie 30-year averages).

  11. How reliable are IPCC 5th Assessment Predictions?  Were they smarter than a 5th grader?

    First the IPCC--Predictions are based on the assumption that CO2 is a primary driver of earth surface air temperatures. Because it has been extremely easy to to predict CO2 levels going forward from 2006, the baseline year for the IPCC 5th, the predictions would not have significantly changed if 12 years later, the actual CO2 levels were inserted (no assumptions) and the predictions recast.  Given that, the average IPCC error from 2007 through 2018 was .14 degrees C.  

    5th Grader: Let's pick a panel of 5th grader that is smart enough to know that they have no clue as to what next years global earth temperature is going to be.  So they decide to guess the prior years temperature. Given that, the average 5th Grader error from 2007 through 2018 was .07 degrees C--twice as accurate as the IPCC Model.

    Here is the data.

    IPCC 5th Model Errors Avg Abs Errors

                                 Avg Err   0.072       0.145
                                     Temperature Model Errors
    Yr        NASA   IPCC          No Idea      Model
    1970   (0.13)

    2006     0.48   0.57

    2007     0.44   0.58             0.04         0.14
    2008     0.38   0.59             0.06         0.21
    2009     0.47   0.62             0.08         0.15
    2010     0.53   0.64             0.06         0.11
    2011     0.45   0.65             0.08         0.20
    2012     0.48   0.68             0.03         0.20
    2013     0.50   0.74             0.02         0.23
    2014     0.59   0.76             0.09         0.16
    2015     0.71   0.75             0.12         0.05
    2016     0.82   0.79             0.12         0.04
    2017     0.72   0.80             0.11         0.09
    2018     0.65   0.81             0.07         0.16
    2019     0.83

    CO2 Levels Mauna Loa Observatory

    Can it be argued that the 5th graders cheated by reassessing every year. Sure. But two facts do not change.

    1) IPCC could have used actual CO2 data and not improved accuracy.

    2) If physics is at all understood, any model based on sound physics should be able to beat the static forecast (e.g., a ball being thrown with elevation above ground being predicted).


    [DB] "Predictions are based on the assumption that CO2 is a primary driver of earth surface air temperatures"

    You clearly didn't read the post.  Models are built using physics and observations; predictions coming from them are an outgrowth of that.  While imperfect, they are demonstrably reliable.  The radiative physics of greenhouse gases like CO2 are well-researched, well-established and accepted by every international science body of note and by the petroleum extraction companies themselves.

    Simply making things, as you do, up is unhelpful.  Please cite sources for claims, per the Comments Policy.

    Inflammatory snipped.

    Please limit image widths to 450.

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