The population explosion: why we should care and what we should do about it.

• Author: Ehrlich, Paul R.
• Position: Symposium on Population Law

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.

1. 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.

   1. 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.

   Employing energy use as the standard, the scale of the human enterprise has grown about twenty-fold since 1850.(4) During that time, per capita energy consumption has risen about five-fold globally,(5) and the population has grown about four-fold.(6) Roughly then, population growth can be considered to be responsible for about 45% of humanity's environmental peril: the combined risks accrued as a result of increasing worldwide environmental impacts.(7) The risks arise from human-caused worldwide changes such as widespread habitat destruction (e.g., deforestation, desertification, urban construction), alteration of the composition and geochemical processes of the atmosphere (e.g. the addition of excess greenhouse gases, depletion of stratospheric ozone, generation of air pollution), overdrafts of groundwater, soil depletion and erosion, water pollution, disruption of the hydrologic, carbon, and nitrogen cycles (among others), and general toxification of the planet. These and many other factors combine into an unprecedented assault on the life-support systems of civilization: the global cycles and natural ecosystems that supply indispensable goods and services to humanity.(8)

   These mostly unappreciated but indispensable benefits include the maintenance of the quality of the atmosphere, regulation of the climate, provision of food from the sea, replenishment of soils, control of pests, and other vital underpinnings of agriculture, production of timber, medicines, and myriad other industrial materials, and regulation of freshwater flows (including controlling floods and droughts) and other forms of weather amelioration.(9) Natural ecosystems also maintain a vast genetic library from which humanity has already derived all manner of things, including domesticated plants and animals, and which is essential to their continued usefulness.(10)

   The I = PAT equation carries an especially important lesson for Americans. It is customary to think of poor nations as overpopulated compared to rich ones, but in terms of global environmental impact, exactly the opposite is true. It is true that most European nations and Japan have greatly slowed, halted, or even reversed their population growth, while most developing nations continue to expand their population sizes at rates of 1.5% to 3.5% per annum.(11)

   But when consumption, the A x T factor ([E.sub.pc]), is considered, an entirely different picture emerges. Thus, around 1990, the average American used some 11,100 watts (11.1 kilowatts, kW)(12) per person, more than ten times as much energy as the average citizen of a developing country.(13) In actuality, the gap between the United States and developing nations is often much wider. For example, the United States in 1990 used 195 times as much commercial energy per capita as Madagascar, 20 times that of Zambia, and 13 times that of China.(14) In other cases, it was narrower: eight times that of Malaysia and six times that of Mexico.(15) Using commercial energy as a measure excludes the use of gathered wood, crop residues, and animal wastes as fuel by poor farmers, so the actual per capita energy consumption in very poor countries is somewhat understated. And in some developing nations such as China, Indonesia, and Malaysia, commercial energy use is growing very rapidly.(16) Nevertheless, the overall picture is quite clear.

   The United States already has the world's third largest population, 268 million people. China is number one with 1.24 billion, India number two with 970 million, and Indonesia number four with 205 million.(17) Compared to other industrialized countries, the American population is growing at a record rate of more than one percent per year (if immigration is included). When the population figures are added to energy consumption it is easy to see why the United States can be called the most overpopulated nation.(18)

   By assaulting earth's ecosystems, humanity is, in essence, sawing off the limb on which it perches. Population growth is clearly a major force behind the saw. The chances of successfully feeding and otherwise caring for an expanding population are being continuously diminished. That is why all human beings should care deeply about the population explosion and, because of their own disproportionate environmental impacts, why Americans should show particular concern.

2. WHAT SHOULD BE DONE ABOUT THE POPULATION EXPLOSION?

   It is a great deal easier to explain why the population explosion should be a critical issue for all of humanity than it is to find one's way through the manifold issues of what ought to be done about it.

   1. Basic Goals

      The easiest answer to the question above is move as rapidly as is humanely possible toward an optimum sustainable population size. But this vague answer immediately raises a series of obvious questions: What is an optimum sustainable population size? What steps would move society in that direction? How does one establish what is humane? Science can put theoretical bounds on the answer to the first question, since there is a biophysical upper limit on the number of people that could be supported over the long term with a given set of technologies and social (including political and economic) arrangements.

      But most people would probably agree that there is a considerable difference between the largest sustainable population and an optimal sustainable population. Few would find supporting the maximum number of human beings, in a situation somewhat analogous to the way battery chickens are reared, to be optimal. Many would desire varied diets, comfortable homes, opportunities for travel and solitude, uncrowded living conditions, and other amenities, all of which would reduce the number of people that could be sustained. With an approximation of current conditions, it has been estimated that the upper bound of an optimum population, one that would in some sense allow for a maximum quality rather than quantity of human life over the long...