September 8, 1998
By Carl Haub
(Carl Haub is the senior demographer of the nongovernmental Population Reference Bureau.)
Global population will hit 6,000 million next year. Five thousand million was reached just 12 years ago, in 1987. That fact alone reminds us that the contemporary explosion in world population is far from over.
Where does the world population situation stand and what can we reasonably expect for the future?
To consider the first of those questions, we have to rewind the clock a bit, back to the 1960s, when there was no doubt in anyone's mind that world population was indeed exploding. In 1960, global population had just reached 3,000 million. The addition of the third thousand million had taken the remarkably short time of 30 years.
Paul Ehrlich's classic book, "The Population Bomb," appeared in 1968, and it opened by asserting that the battle to feed all of humanity had been lost. It is hardly the fashion today to offer any sort of defense of Ehrlich and those seen as the Cassandras of the past, but perhaps it is useful to take a look back and reconsider.
Ehrlich's warning helped set the tone for the period. Such concerns were justified in the context of the times. In the 1960s, world population was growing at its fastest pace in history. The developing countries were increasing at the remarkable rate of 2.5 percent per year and they held more than 70 percent of the world total. At such a rate, their numbers would double every 27 years. This was all the more daunting when we realized that it took until 1800 for all of human history to reach the first thousand million and until 1930 to reach the second.
Why did this explosion occur?
Death rates in developing countries fell precipitously after World War II. Public health and inoculation campaigns spectacularly reduced disease and infant mortality. In the developed countries, such declines in mortality had taken centuries as society itself gradually changed, becoming more urbanized and dependent upon large families. As a result, birth and death rates tended to decline in concert, and population growth rates never reached the level that they later would in developing countries. There, death rates fell so quickly that society had little time or reason to change its desire for larger families.
Ehrlich and others who warned of the consequences of unchecked growth are now criticized for their alarmist notions. But the critics often miss the point. In the 1960s, women in developing countries were averaging six children and life expectancy was rising at a pace never before seen. Modern methods of family planning were just becoming known in the industrialized countries, and the prospect that they would become available in the agrarian, traditional societies of the developing countries was dim indeed.
It is precisely because of concern over rapid growth that countries began to adopt national policies to address rapid population growth. We now have a new perspective. Blaming Ehrlich is tantamount to criticizing someone for yelling "Fire!" too loudly.
Today, the global demographic situation is more complex than 30 years ago when all developing country populations were multiplying swiftly. The majority of those countries have adopted population policies that identify population growth rates as too high. Now, family planning has been made available throughout much of the developing world. While population continues to grow, the fertility rate -- the number of children a woman will bear in her lifetime -- has declined. Since 1950, the most rapid population growth has taken place in Africa, Asia (less China), and Latin America. That situation continues today.
Had the birth rate in developing countries remained unchanged since 1950, the population of those countries would today total about 7,000 million and be growing at a rate that would continue to double their populations in less than 20 years! By 2020, it would be about 15,000 million and, less than 20 years later, 30,000 million. That projection, of course, assumes that such unheard of population growth would not have caused serious food shortages, the spread of disease, and untold environmental calamities. In other words, just what Ehrlich was most concerned about.
Today, we know something that writers of the 1960s did not. Couples in developing countries did want to limit their family size, and they often would do so with access to efficient methods of contraception. By no means was this uniform. In some countries family planning would find readier audiences than in others. Still, while the use of family planning is far more common in countries with more rapidly developing economies, it is also in evidence in traditional, rural areas where it was not necessarily expected.
This development has modified our view of future world population growth that now includes a significant possibility: the ultimate end of world population growth at some far off, unknown number. The eventual number will depend entirely upon the course of the birth rate in developing countries.
There is no more important issue than fertility to demographers preparing world population projections. Discussion focuses on the topic of "replacement level fertility." This is simply a family size of about two children per woman, so that each couple just "replaces" itself, and growth in population size ultimately ceases. In some areas of the world, this may seem a distant dream, but at least we know that it is possible. Future zero population growth in developing countries depends upon their achievement of replacement level. Failing that, populations continue to grow.
While we cannot know future world population size today, we can project what future size would be under a variety of different scenarios.
This is what the United Nations Population Division does every two years in its biennial world population projections. The U.N. issues a series of projections that it calls the High, Middle, and Low Variants. These project three very different scenarios for global population. The large differences are due solely to the assumptions made on future fertility in developing countries. This results from the fact that virtually all - 98 percent - of world population growth now takes place in those countries.
Fertility in nearly all developed countries is now below the replacement level and the majority of European countries are headed for population decline.
For its Middle Variant, the U.N. makes the general assumption that the total fertility rate (TFR) for all countries will converge on the replacement level of 2.1 children per woman by the middle of the next century. Under that scenario, world population would rise to a total of 11,000 million and then stabilize.
The statistical importance of the two-child family can easily be seen in the U.N.'s High Variant. If couples worldwide prefer a somewhat higher family size, 2.6 children, world population would grow to a larger size, and not just a little larger. It would swell to 27,000 million people by 2050 and continue to increase.
The Low Variant, on the other hand, assumes that couples everywhere will average a mere 1.6 children, about the present level of the TFR in Europe. That low path peaks at 8,000 million and then begins to decline, since couples are not replacing themselves. These very different scenarios show how very sensitive projected population numbers are to whatever path the birth rate takes.
No matter which scenario one chooses, it is essential to keep in mind that they all assume that birth rates will decline at a steady pace to what are, in truth, rather low historical levels. The reality, of course, will be different. Based on current experience and trends, we can expect fertility to begin slowly declining in some countries, to decline for a time and then level off in others, and to decrease smoothly in still others.
We have examples of all of these patterns. In Thailand, for example, fertility fell to less than two children per couple, facilitated by a well-run national family planning program. A similar pattern is observed in South Korea and Taiwan.
In Latin America, however, fertility shows a pronounced tendency to decline for a time but then pull up short at about three children per woman as in Argentina, Colombia, and Jamaica. In Africa, fertility decline has just begun in some countries but not in many others.
The situation becomes even more complex when we look below the country level. In India, for example, TFR's decline, since the 1970s from 5.5 children per woman to 3.5 today, has largely been accomplished by a TFR decrease in the more prosperous and educated southern states.
Future fertility decline in India will heavily depend upon what happens next in the large states of the north where illiteracy levels are much higher. The state of Uttar Pradesh, for example, with 150 million people (making it equivalent to the world's sixth largest country) and a TFR of five children per woman is a particular challenge.
This century is likely to be remembered for its tremendous surge of population growth. The next century will likely see social and demographic changes that will outweigh even what has happened in the past 100 years.
The balance of world population will shift heavily towards today's developing countries. Perhaps less than 5 percent of world population will live in Europe and North America. That will almost certainly mean a world that is socially and economically much different from today's.
There has been a move now to de-emphasize population growth as yesterday's concern or yesterday's news. But even a cursory look at the numbers tells us that population growth may be a bigger story in the next century than in this one.
(Haub is coauthor of the Population Reference Bureau's annual report "World Population Data Sheet." Findings from the 1998 data sheet can be found on the Internet at: http://www.prb.org/prb/info/98wpds.htm)