Why model climate?

I wrote a talk on climate modelling, aimed at the interested-but-non-specialist public.  Here it is.

It touches on:

1) The choices we have to make as a society.

2) The difficulty of doing controlled experiments with a single Earth.

3) The idea of a climate model.

4) A really simple climate model from first principles.

5) How a rotating tank of water is a climate model.

6) That all models are wrong, but some are useful.

7) What a modern Earth System Model looks like.

8) The importance of humans as a driver of future climate.

I’d hope that most of you interested-but-specialists might just enjoy the cartoons, most of which I drew myself.

The talk is a work in progress, and I’ll hope to be replacing the videos with a live rotating-tank demo, and a hand drawn explanation of Earth System models.

I’d appreciate (constructive) feedback, so leave a comment, email me at climatestats@gmail.com, or tweet me @dougmcneall


My thanks to Simon Hammett for the video, to Niall Robinson for organising, and to Tamsin Edwards, Ed Hawkins, Philip Brohan and Ruth Dixon for feedback. You can find links to the videos embedded in the talk below:




  1. Great video presentation, I like the way slides and you as speaker are all on same view, all very clear. The cartoon sketches are excellent. I think that, at this scale, the last slide on high versus low mitigation would be clearer if only top pair Earth views are shown on the slide, maybe a slide each for temperature and aridity.

    Just one caveat – potentially in need of correction (if I’m right of course, I’m no climate scientist!).
    In the section (about 8 min onward) for the simple climate model balancing energy in and emitted energy you say (at 8m44s) that the temperature result is 288K = 15ºC. But isn’t the whole point of showing this equation that it gives the temperature for the Earth surface as it would be *without* an atmosphere and that in fact the result is surprisingly cold, about 254K or -19ºC. => As in same calculation shown here: http://www.windows2universe.org/earth/climate/sun_radiation_at_earth.html

    Hence we know that some other factor(s) are missing from this simple model, primarily the greenhouse effect as it turns out, so that the actual temperature was about 14ºC pre-industrial and now closer to 15ºC. Have you skipped the greenhouse gas step in your explanation?

    1. Hi Paul,

      Good catch, I have indeed skipped the “greenhouse” step in the explanation – but with good reason, I hope. The zero-dimensional EBM is simple but powerful enough that it can give us quite good insight into the system. Here, I wanted a simple example, without explaining *too* many physics principles like a “black body” vs. a “grey body”, and getting distracted by explaining the greenhouse effect. I agree that the difference between the “black body” and “grey body” calculations is an interesting thing in itself, and very useful if the greenhouse effectis one of the things that you are explaining. Indeed, finding the “black body” vs. “grey body” solution was the first problem in the climate dynamics course for my Masters, if memory serves 🙂

      There is an excellent description of the calculations you describe from Penn State here, and the “grey body” extension here.

      In the text, it says:

      “Various gray body parameter choices for A and B have been used by different researchers, in different situations”. In this case, I was choosing the parameter settings to suit my lecture – in effect, choosing a particular way that the model is “wrong”. A wider discussion on other ways that the model is “wrong” (but also useful) is welcome.

      Thanks for the feedback.


  2. Glad I got that right, thanks for the links, had not seen that site before, very clear. If I get time out from my real job I will spend some time there.

    FWIW I don’t think skipping the greenhouse step in the explanation is a good idea at all. Surely, even in explaining climate change to non-experts it is an absolutely key step? Putting the incorrect temperature result for the black body made this part of the explanation completely distracting, for me at least, especially as your intent was to look at ways in which a basic EBM is “wrong”.

    I definitely recommend putting this step back in for the next outing of this talk. After all this step is the first and most important way in which a simple EBM is incorrect, showing both how essential the green house effect is for life on Earth, how sensitive the climate system is to our carbon emissions and how dangerous rapid climate change is likely to be if unmitigated. One extra slide is all that’s needed to show how Earth is more than 30ºC warmer than it would be without the greenhouse effect.

    Btw, though I had seen it before, the ‘weather in a tank’ video is absolutely brilliant practical illustrative science, good to watch it again.

  3. Hi Paul,

    Except I wasn’t trying to explain climate change – I was trying to give an account of how modelling a system is useful. These things are different; my objectives are not the same as yours.

    Also, I wasn’t doing the black body calculation, I was doing the grey body calculation.

    Thanks again.


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