Limits to growth may be subtle but still inexorable

Sir

Dick Taverne, in his review of James Gustave Speth's recent book Red Sky at Morning, comments about a “wildly inaccurate” 1972 report by researchers at the Massachusetts Institute of Technology (MIT): “The Limits to Growth predicted that we would run out of gold, zinc, mercury and oil before 1992” (“When greens see red”, Nature 432, 443–444; 2004). This is a very common myth which needs correction.

The precipitous collapse of economic growth projected by the MIT report does not occur before 2020 in any of the model runs, so it is hard to see how its doomsday projections have been disproved. For a 30-year-old projection using some eight state variables, the MIT model did a surprisingly good job of predicting where we were in 2004, as an update shows (D. A. Meadows et al. Limits to Growth: 30 Years On, Earthscan, London, 2004).

One run of the model even had the natural-resource constraint removed by assuming an unlimited source of energy.

The model's mechanism of collapse is more subtle than simple resource exhaustion. Suppose, as an example, that when the Chinese want to replace the steel mills they are now building, they find that materials are available but costs are 10 times higher, while their productivity in the interim has only doubled. Hard-pressed to keep steel production growing at all, they will have even less mill capacity available to make materials for replacement in following years, and so eventually will be overwhelmed by the spiralling legacy of repairs.

Whether or not this is a model for a reckless world's future, failure of revenue to cover accelerating physical depreciation is a frequent explanation for urban decline.

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Fisk, D. Limits to growth may be subtle but still inexorable. Nature 434, 271 (2005). https://doi.org/10.1038/434271b

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