Academic journal article
By Ehrlich, Paul R.; Ehrlich, Anne H.
Environmental Law , Vol. 27, No. 4
Almost everyone has heard about the population explosion, but few people understand its significance. Following is a brief overview of the basic problem caused by the rapid increase in human numbers from roughly one billion people in 1800 to some, six times that number less than two centuries later. Half of that growth has occurred just since 1960, and it appears that, at a minimum, two to three billion more people--and possibly several billion beyond that--will be added to the population before growth ends (assuming a disastrous die-off can be averted). The significance of numbers in the billions is often difficult to grasp; suffice it to say the world is annually adding roughly the population equivalent of present day Germany, and that perhaps thirty to fifty more `Germanys' are likely to be added to the population before reduced birth rates can bring growth to a halt.
I. WHY IS THE POPULATION EXPLOSION IMPORTANT?
If one asks this question of an acquaintance, the answer often focuses on crowding. A resident of the San Francisco Bay area might mention the perpetual traffic jams on the freeways. Or there might be some comment about starvation in Africa, or the flow of refugees into California from Mexico and the resultant strain on school and health budgets. While there is a population component in those problems, such answers do not get to the most important consequences of overpopulation. Moreover, debates about the roles of women in society, and particularly battles over whether women should be required by the government to carry fetuses to term, have given many Americans the misimpression that population problems should be viewed mainly as issues of the reproductive rights of individuals. In the extreme, this narrow focus has led the uninitiated to claim that there is no connection between the size of the human population and environmental problems.(1) All these views miss the main point.
A. Population Impact on Life-Support Systems
The overriding reason to care about the population explosion is its contribution to the expanding scale of the human enterprise and thus to humanity's impact on the environmental systems that support civilization. The number of people (P), multiplied by per capita affluence (A) or consumption, in turn multiplied by an index of the environmental damage caused by the technologies employed to service the consumption (T), gives a measure of the environmental impact (I) of a society. This is the basic I = P x A x T identity, often just called the "I = PAT equation."(2) A useful surrogate for the A x T of the I = PAT equation is per capita energy consumption ([E.sub.pc]); hence I = P x [E.sub.pc].(3) Almost all of a society's most environmentally damaging activities involve the mobilization and use of energy at high levels, including the manufacture and powering of vehicles, machinery, and appliances; constructing and maintaining infrastructure; lighting and heating buildings; converting forests into paper, furniture, and homes; producing inputs for, and processing and distributing outputs from, high-yield agriculture; and so on.
The surrogate formula has some drawbacks, however. At the lowest levels of development, energy use probably underestimates environmental impact. For example, very poor people can cause serious environmental damage by cutting down trees for fuelwood. At the highest development levels, energy use probably overestimates environmental impact: a given amount of energy use in Western Europe, Japan, or the United States undoubtedly provides more benefits and does less damage than the same amount used in Poland or Russia because of much greater efficiency and stricter environmental regulation. Yet, despite these imperfections, for comparisons between nations or for intertemporal comparisons, energy use seems to be a priori a reasonable measure that correlates with many types of environmental damage. It certainly is the most readily available statistic with those characteristics. …