There has been criticism of the World3 model. Some has come from the model creators themselves, some has come from economists and some has come from other places. In the book
Groping in the Dark: The First Decade of Global Modelling,
Donella Meadows (a
Limits author) writes: We have great confidence in the basic qualitative assumptions and conclusions about the instability of the current global socioeconomic system and the general kinds of changes that will and will not lead to stability. We have relatively great confidence in the feedback-loop structure of the model, with some exceptions which I list below. We have a mixed degree of confidence in the numerical parameters of the model; some are well-known physical or biological constants that are unlikely to change, some are statistically derived social indices quite likely to change, and some are pure guesses that are perhaps only of the right order of magnitude. The structural assumptions in World3 that I consider most dubious and also sensitive enough to be of concern are: • the constant capital-output ratio (which assumes no diminishing returns to capital) • the residual nature of the investment function • the generally ineffective labour contribution to output A detailed criticism of the model is in the book
Models of Doom: A Critique of the Limits to Growth. Czech-Canadian scientist and policy analyst
Vaclav Smil disagreed with the combination of physically different processes into simplified equations: He does however consider continuous growth in world
GDP a problem: {{blockquote|Only the widespread
scientific illiteracy and
innumeracy—all you need to know in this case is how to execute the equation y = x * e^{rt}—prevents most of the people from dismissing the idea of
sustainable growth at healthy rates as an oxymoronic stupidity whose pursuit is, unfortunately, infinitely more tragic than comic. After all, even cancerous cells stop growing once they have destroyed the invaded tissues. point out that the methodology of such models may be valid empirically as a world model, but might not then also be useful for decision making. The impact data being used is generally collected according to where the impacts are recorded as occurring, following standard I/O material processes accounting methods. It is not reorganized according to who pays for or profits from the impacts, so who is actually responsible for economic impacts is never determined. In their view • The economic motives causing the impacts, that might also control them, would then not be reflected in the model. • As a seeming technicality, it could bring into question the use of many kinds of economic models for sustainability decision-making. The authors of the book
Surviving 1,000 Centuries consider some of the predictions too pessimistic, but some of the overall message correct. At least one study disagrees with the criticism. Writing in the journal
Global Environmental Change, Turner notes that "30 years of historical data compare favorably with key features of the 'business-as-usual' scenario called the 'standard run' produced by the World3 model". ==Validation==