Low fertility and sustainability.

• Author: Riche, Martha Farnsworth

Motivation to stabilize population can be undermined by excessive worry that smaller numbers of young people will be supporting larger numbers of the elderly. But prevailing patterns of behavior and resource allocation can be changed in ways that reduce pensioner/worker ratios and make population stabilization more politically viable.

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Until a few years ago, environmentalists led the call for "population control" in the cause of sustainability. Their ideas about limiting fertility so enraged global women's advocates that population didn't even make the agenda at the 1992 Rio conference on the environment. When the United States developed a new, consensus-based position for the International Conference on Population and Development, held in Cairo in 1994, many environmentalists contested the new focus on helping women around the world have as many or as few children as they wanted. When I explained the "Cairo Consensus" at a town meeting in San Antonio, Texas, one man responded, "For the next 20 years no women should be allowed to have children, and only one in 20 should be allowed to have one child for the following 20 years!"

Now even staunch sustainability supporters are beginning to worry that unprecedented low fertility rates in some countries threaten sustainability by population declines. Why the turnaround, especially when the world is adding to its numbers rapidly? The answer seems to be a fear that declines in some countries will take hold globally, and then we'll all go to hell in a hand-basket. Or, as Michael Teitelbaum and Jay Winter, authors of The Fear of Population Decline, put it, "If and when population decline takes place, there are both rational and irrational reasons to pay attention. All too often over the past century, the irrational has provided a convenient means of explaining away social, political, and economic problems by invoking distorted metaphors from biology."

Let's calm down and take a reasoned look. First, the population declines expected in countries such as Germany, Japan, and Italy are taking place while world population keeps growing. The United Nations currently projects that world population will rise from its current level of 6.4 billion to somewhere between 7.4 and 12.8 billion by 2050, attaining between 5.5 and 43.6 billion by the end of the century. Demographers find both the high and low bounds to these longer-term projections illustrative but unrealistic; their purpose is to delimit the range of possibilities suggested by current trends. However, many non-demographers are treating the low projection as gospel. This scenario assumes that fertility in all countries will fall to around 1.6 children per woman (the average level expected for Germany, Italy, and Japan) and never again attain the two-child "replacement" level.

Demographers still don't know to what extent very low fertility is temporary (the result of shifting to later child-bearing) or permanent (a change in ideal family size). As John Bongaarts of the New York-based Population Council says, "It's fair to say that the demographic community has been surprised by these trends."

(This isn't the first time fertility swings have surprised demographers. Most Americans are aware that a Baby Boom erupted after World War II and lasted until the Pill gave women control over their fertility, but few now remember the downturn in births before the boom. In an illustration of how new developments cause good projections to go bad, Philip Hauser projected in the 1940s that U.S. population would peak in 1990 at 190 million! In 2004, we're more than 100 million past that "peak." That's why demographers don't view projections as predictions, but simply as illustrations of how things could go absent new developments, whether willed or unanticipated.)

Demographers have not yet untangled the relative impact of the reasons for very low fertility, either, but have reached consensus that the overall cause is the changing costs of rearing children under "modernization." Modern...