HOW MANY angels can dance on the head of a pin? This is a type of question that people asked in the not-so-distant past when religion reigned supreme, and science and technology played a negligible role in everyday life. Now that the rise of science and technology has enabled enormous increases in the human population, we must face the question: How many people can live on the surface of the Earth?
The rate of growth, that is, the percentage increase per year, of the human population is at an all-time high. Many politicians, economists and religious leaders regard rapid population growth "natural" and extol its virtues. For example, we often read that population growth stimulates the economy and is, therefore, good. This may be true if one's vision is expressed in units of four years and limited to a few decades at most. However, life has existed on Earth for at least 3.5 billion years and human beings for a few million years. So the very rapid population growth of the past 100 or so years is not natural.
If the current rate of growth of world population, about 2 percent per year, were continued into the year 3400, then each person who is now alive would have 1 trillion descendants, and the total human population would be about 10,000,000,000,000,000,000,000 (10 sextillion). This is 10 percent of the total number of stars in the entire observable universe. Well before 3400, the average amount of land per person would have diminished to less than one square inch.
Broken down into shorter intervals, we are talking about a tenfold increase in just over a century. So by about the year 2100, at current rates, there would be 50 billion people on Earth. And 500 billion not long after the year 2200.
What about covering all the deserts and oceans with people? That would only delay the inevitable need for zero population growth by a century at the very most. How about shipping off the extra people (net difference between the number born and the number who die) to outer space? At current growth rates that would mean sending 10,000 people up every hour of every day. And we have trouble launching a few shuttles per year safely.
The issue is not whether an economy that is stimulated by population growth is good, bad or indifferent. The above calculations show that growth is impossible except in the very short run. The real issue is what kind of world will the people of the present and next few generations leave for the people and other creatures of the next few millennia?
According to Jared Diamond, professor and biologist at the University of California, Los Angeles, the coming century will witness one of the worst extinctions in the history of life on Earth. Roughly one-half of the 30 million species that are estimated to exist will become extinct, courtesy entirely of human beings. If yet additional population and economic growth of the sort that some people espouse actually occurs, then the extinction rate will be even worse. A combination of far too many people, greed and unbridled technological power is destroying the natural world.
Each person plays a role in the population equation. If you and your spouse have two children and four grandchildren then you are reproducing at replacement levels (zero population growth). But if you have four children and they, in turn, each have four children so that you have 16 grandchildren, then that is roughly equivalent to the 2 percent per year growth rate that characterizes the world as a whole.
Each of us has his or her own system of values. For me, a planet with relatively few people, each of whom can live with dignity and a high quality of life, is far superior to a world where too many people, awash in pollution, stretch resources to the breaking point, and where billions struggle to survive at mere subsistence levels.
Benjamin Zuckerman is a professor of astronomy at UCLA and a member of Zero Population Growth.