J. W. Forrester, an outstanding electrical engineer and management scientist at MIT, proposed to advance this kind of analysis with a great leap forward. His model did not represent the management of a specific species like whales, but rather the interaction between humankind and planet Earth. It had not one, but two limiting factors: the capability of the Earth to provide resources like food, z timber, metals, etc., and the capability of the Earth to absorb pollutants like toxic waste, smog generating aerosols, etc. The goal variable was quality of life, and humans were assumed to try to increase their quality of life by increasing their number as well as the size of their capital equipment. The result was a grim scenario of overshoot and collapse within a few decades.
Forrester's model was presented to a world audience by Meadows et al. in 1972. The model was not performing any optimization exercise; it was comparing different strategies, showing that many intuitively plausible strategies - such as increasing capital accumulation to abate pollution - could not avoid the pattern of overshoot and collapse. What was required, these authors argued, was an end to population growth as well as economic growth.
With regard to population growth, most authors agreed and still agree that it would be highly problematic if humankind would keep growing toward 10 billion people in the foreseeable future. However, there is also a widespread agreement that global population growth is declining and will come to an end without overshoot and collapse. In contrast to other biological species, with humankind, population growth is slowed down by increased well-being.
With regard to the economy, however, the claim of limits to growth immediately triggered a fierce debate. Robert Solow, also an economist at MIT (and Nobel Prize winner in 1987), wrote: ''I would like to state, briefly and bluntly, why I think the various 'doomsday models' are worthless as science and as guide to public policy'' (Solow, 1972: 3832). His main point was that that the price mechanism would enable humankind to avoid overshoot in the face of limited resources by triggering substitution and innovation. During the following decades, economists developed models representing these mechanisms. A key claim of this kind of literature is that resource scarcity is not a big problem because it is precisely what markets can deal with, and that pollution increases with economic growth only in the early stages of economic growth. Once people get more affluent, they are supposed to be able and willing to abate pollution by technological means.
The debate took a new twist with the publication of the report Our Common Future. This report launched the concept of sustainable development, claiming that it was necessary and possible to develop new patterns of economic growth that would balance ecological, economic, and social needs. While the report steered clear of mathematical models and detailed empirical studies, it displaced the image of limits to growth in favor of the vague but attractive concept of sustainable development.
The debate on limits to growth is far from over, however. On one hand, the combination of environmental and political challenges raised by the globalizing economy of our time leads some authors to think again about the prospects of life beyond economic growth. On the other hand, there is a long-standing tradition of economists seeing economic growth as a transitory phase in the history of humankind - Ricardo, J. S. Mill, Marshall, Pigou, Keynes, Hicks all shared this view.
But while Ricardo emphasized the problem of limited resources already nearly two centuries ago, the main point of this tradition is a different one. In the famous words of John Stuart Mill, ''I confess I am not charmed with the ideal of life held out by those who think that the normal state of human beings is that of struggling to get on; that the trampling, crushing, elbowing, and treading on each other's heels, which form the existing type of social life, are the most desirable lot of human kind, or anything but the disagreeable symptoms of one of the phases of industrial progress'' (Mill, 1848: Bk iv, ch. vi, §iv.6.5).
See also: Biological Control Models; Statistical Methods.
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