Carrying Capacity

The concept of carrying capacity is borrowed from ecology, where it is defined as the maximum number of a given species that can be supported indefinitely in[Page 26] a given habitat without permanently reducing its productivity. This definition needs to be modified for humans because they can eliminate competitive species, import resources, and adopt technologies to sustain numbers.

Human carrying capacity is particularly difficult to predict because it depends not only on poorly understood natural constraints, such as sustainable soil fertility and climatic uncertainties, but also on a whole gamut of socioeconomic factors, such as migration, demography, values and fashions, individual versus collective choice, and even religion. And in a world where trade is global and commons such as the seas and atmosphere are shared, the notion of carrying capacity at anything but the global level is not helpful.

It is useful to distinguish between the actual population that can be sustained under a possible technological fix (biophysical carrying capacity) and the number that might be sustained under a pattern of resource consumption associated with a particular social system (social carrying capacity). At any level of economic development, the social carrying capacity will always be less than the biophysical one. After all, no one wants to live like factory-farmed animals or to live on a diet of bread; choice and freedom of action are part and parcel of development, and not all states will want to eat from the same menu. It is also worth noting that technological fixes cannot make the biophysical carrying capacity infinite because ultimately there are technical limits to photosynthetic efficiency and the production of carbohydrates.

Models of global carrying capacity have varied dramatically in their predictions. The Limits to Growth study published by the Club of Rome in 1972 predicted, rather pessimistically, that within 100 years of that time society would run out of renewable resources, leading to a precipitous collapse in the world economic system and food production and ultimately resulting in a soaring increase in the death rate and disastrous population decline.

In contrast, optimistic models, such as that put forward in The Next 200 Years: A Scenario for America and the World, predict a densely populated world with no poverty and humans in control of the forces of nature. Optimistic scenarios are contingent on continually improving technologies developed as and when needed. This is a somewhat utopian vision given the repeated catastrophic impacts of hurricanes on the U.S. Gulf Coast and the prolonged droughts in the Sahel.

Maintaining any carrying capacity requires sustainability, and there are reasons to believe that many global resources are becoming severely degraded. Irreversible land degradation is widespread, atmospheric pollution is a feature of many industrial regions, and even the oceans are not without damage as measured by the catastrophic decline of many of the oceans' fish stocks. All of these impacts indicate beyond any doubt that global social carrying capacity has already been exceeded. And carrying capacity models have not even begun to include variables such as global warming. Even if people can be persuaded to change their lifestyles, maximizing carrying capacity requires better social, political, and economic global governance.

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