ABSTRACT
How many human beings can the earth support? This question is unanswerable without also defining the life-style and consumption patterns of the people in question, and the length of time that they are to be supported. Unlike other animals, human beings are capable of adjusting their levels of resource consumption enormously, largely through the use of technologies with which they can mobilize otherwise inaccessible resources and divert much of the productivity of the biosphere to their own uses (Vitousek et al, 1986). Given that the earth’s daily energy income (from the sun) is limited, as is the amount of energy stored from past solar income (fossil fuels), there are ultimate constraints on the number of human beings that can be supported. Moreover, civilization is living beyond its means in so far as it depends for support on past-stored energy, reduces the fraction of current energy income made available through photosynthesis, and degrades and disperses its finite material resources. Biologists would say it has exceeded its carrying capacity (Ehrlich and Ehrlich, 1990; Daily and Ehrlich, 1992).
