WORLD3-03

This is the latest instance of the WORLD3 model, as in Limits to Growth – the 30 year update, from the standard Vensim distribution. It’s not much changed from the 1972 original used in Limits to Growth, which is documented in great detail in Dynamics of Growth in a Finite World (half off at Pegasus as of this moment).

There have been many critiques of this model, including the fairly famous Models of Doom. Most are ideological screeds that miss the point, and many modern critics do not appear to even have read the book. The only good, comprehensive technical critique of World3 that I’m aware of is Wil Thissen’s thesis, Investigations into the Club of Rome’s WORLD3 model: lessons for understanding complicated models (Eindhoven, 1978). Portions appeared in IEEE Transactions.

My take on the more sensible critiques is that they show two things:

  • WORLD3 is an imperfect expression of the underlying ideas in Limits to Growth.
  • WORLD3 doesn’t have the policy space to capture competing viewpoints about the global situation; in particular it does not represent markets and technology as many see them.

It doesn’t necessarily follow from those facts that the underlying ideas of Limits are wrong. We still have to grapple with the consequences of exponential growth confronting finite planetary boundaries with long perception and action delays.

I’ve written some other material on limits here.

Files: WORLD3-03 (zipped archive of Vensim models and constant changes)

5 thoughts on “WORLD3-03”

  1. Thanks for posting the World3 model, it is not included in teh 30th Anniversary CD and I’ve been looking for it everywhere.

  2. Thank you for putting the model onto your page – the original book has it but print is so small and I needed a version that I could use within a dissertation and like the other comment the new book does not have it in.

    I agree that the model is simplified and does not take into account a number of factors, but like all models it is indicative rather than utterly accurate. I agree that the warning and the call for radical change still stands today.

  3. Hello Tom,

    Many thanks for your superb blog. I’m going to tell all my friends about it.

    I learned of you via your excellent [vimeo video](https://vimeo.com/177495412):
    Vensim Model Analysis – World Dynamics

    A few words about myself. Science is my hobby. Stephen Jay Gould’s books got me hooked. I read Science and Nature magazines every week. I’ve also read Foreign Affairs magazine for over 40 years. None of which makes me a scientist or foreign policy expert. I am a fan of [Peter Sinclair’s Climate Denial Crock of the Week](https://climatecrocks.com/) and have contributed financially to his work.
    I have a bachelors in math and masters degree in computer science, but know very little about modeling except that it isn’t a hoax 🙂

    Here, I’d like to ask a question about “model denial”. [This page](https://majorityrights.com/weblog/comments/forresters_limits_to_growth_model_for_your_personal_computer/)
    contains the following from karlmagnus:

    QQQ
    Don’t know about this version, but the original model included exploding exponential error terms. IF you have a model like Forrester’s with exponentials all over the place, and run a 40 year projection, the error terms explode off the screen, so “catastrophe” of some kind is unavoidable whatever assumptions you put in. I told Forrester this in a public meeting in October 1971; didn’t stop the charlatan propagating his nonsense.
    QQQ

    The last sentence marks this guy as a crank, but the critique is “mathy” enough so that I can’t clearly refute it. It misleads with a half truth, namely that roundoff and other numeric problems must be taken seriously in all computer calculations. So my question is, how would you respond?

    Your work is fascinating. I have lots of other questions, but I’ll leave them for later.

    Edward

    1. Hi Edward –

      This strikes me as a completely vacuous statement. “Error terms” in particular has no obvious meaning. Is karlmagnus asserting that the economy is not growing exponentially? Or that positive feedback doesn’t exist?

      Ironically, you could paraphrase km’s comment to something like, “exponential growth always comes to a catastrophic end,” in which case he’s essentially asserting the Limits message.

      I’d put this in the “crank” bucket. There are legitimate critiques of World3 formulation issues (see for example Will Thissen’s thesis). This is not one.

      Tom

  4. Yeah, we both agree about km. Let’s forget about him and see if we can improve my intuition. Unless I am mistaken, the farther out a weather forecast goes, the less reliable it is, presumably because the initial conditions aren’t known perfect. Or maybe for other reasons. Otoh, climate models don’t seem bothered by such things. So two questions:

    1. Why aren’t multi-year simulations like weather forecasts?
    2. Why don’t uncertainties “build up” in climate models and world3?

    I may be missing something really basic, but I don’t know what it is. Are there any better questions to ask?

    Edward

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