Global Change and Our Common Future Papers from a Forum (1989) / Chapter Skim
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3. Global Change and Carrying Capacity: Implications for Life on Earth
3. Global Change and Carrying Capacity: Implications for Life on Earth
Pages 19-28
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From page 19... ...
Applying the reasoning of Liebig's ''law of the minimum," overall carrying capacity is determined by whichever component yields the lowest carrying capacity. Much of our discussion here focuses on food because, although it may not ultimately be the limiting resource of human population size, food production is a crucial factor that is very sensitive to global change.
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From page 20... ...
In the following, we discuss the reduction in carrying capacity that can be expected to result from direct human impacts on resources and the environment and from our indirect impacts on the climatic system. DIRECT HUMAN IMPACTS The Stanford Carrying Capacity Project has estimated that the human population now uses directly, coopts, or has destroyed approximately 40 percent of global net primary productivity on land, the basic food supply of all terrestrial animals (Vitousek et al., 1986~.
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From page 21... ...
and for the development of new crops that could improve diets of human populations in the tropics (Ehrlich and Ehrlich, 1981~. Even more threatening than these direct effects of the human population on local and regional carrying capacities are human impacts that operate by changing global systems indirectly.
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From page 22... ...
, due mainly to three changes: abandonment of deteriorated land; conversion of cropland to nonfarm uses, especially in densely populated regions; and set-asides in the United States. The primary prospect for expanding food production thus rests with the potential for increasing yields through more intensive cropping, increased fertilizer use, or development of more productive strains.
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From page 23... ...
, the all-time record food production of 1985 could have provided a minimal vegetarian diet to about 6 billion people, a number projected to be exceeded within the next decade. The same global harvest, allowing a diet with about 15 percent animal products, could feed some 4 billion people.
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From page 24... ...
Under our most "pessimistic" scenario, the mean time between unfavorable climatic events was 3.3 years, and each event caused a 10 percent drop in grain production below the trend. In order to simulate the feedback between availability of food and population size, it was assumed that a food deficit of 1 metric ton of grain resulted in two incremental deaths.
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From page 25... ...
The model is, of course, simply an aid to thinking about the possible consequences if short-term climatic change were to cause drops in grain production of a magnitude roughly comparable to those known to have been caused before, and considering the rest of the system to be essentially Surprise free." Our results are not predictions; they are simply indications of the nature of problems that may occur if the global warming leads to an increased frequency and severity of climatic events deleterious to agriculture. CONCLUSIONS The population-food system has no '"fail-safe" backup mechanisms designed into it, even if climates should remain very favorable to food production.
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From page 26... ...
1974. Human population and the global environment.
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From page 27... ...
In H.J. de Blij, ea., Earth '88: Changing Geographic Perspectives, pp.
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