It's not often that a scholarly paper declares its implications "momentous," but a newly released report by the United Nations Population Division does just that. And with good cause. In a proposal sexily titled "The Future of Fertility in Intermediate-Fertility Countries," the U.N. concludes that in this century we can expect a "slowing of population growth rates" followed by "slow reductions in the size of world population."

Yes, you read it right: "reductions." That means we are less likely to "run out of resources," burn ourselves up with global warming or be overrun by a great dusky horde of Third World immigrants. (What will Jeremy Rifkin and Pat Buchanan write about?) Instead we'll have to deal with the problems--and opportunities--that come with a shrinking population.

On the surface, this is a statistical matter. But it deals with a statistic upon which much of the current global belief system rests. The background is important. Although the U.N. projects three alternative and allegedly equally valid projection series, "High," "Low" and "Medium," it is Medium that is the Mama Bear and gets all the attention. The word may be "medium," but as it plays out it reads "most likely."

And what was most likely in the earlier medium projection was a massive increase in population, climbing from 6 billion people today to 9.3 billion by 2050, and topping out at 11.5 billion people in the distant future. Eventually, the “medium variant” projected, every nation would arrive at a total fertility rate of 2.1 children per woman--the “replacement rate,” at which over time a human population stabilizes. This meant low fertility countries would increase their baby production and high fertility countries would lower theirs. In other words, in the long run we might be OK, but in the meantime we’d face “overpopulation.”

Environmentalists, the slow-growth crowd and population-control enthusiasts liked this forecast. The overpopulation crisis was real, inexorable, and growing, they argued. Something had to be done; and they were the ones to do it--if only they had the attention and the funds.

Then reality intervened. Never have birth and fertility rates fallen so far, so low, for so long, in so many places. Europe has now seen 45 consecutive years of fertility decline, from 2.66 children per woman in 1955-1960 down to 1.34 in 2000-2005. Japan has declined from 2.75 to 1.33. The phenomenon is also proceeding in the less developed world, where fertility levels are higher but rates are falling faster than ever seen previously in the developed nations. (See nearby chart.)

The U.N. slowly responded. In 1998, after consultations with demographers, the projections for low-fertility countries were lowered. No longer would countries with incredibly low fertility rates in the range of 1.2 (Italy and Spain) move toward 2.1 by 2050; instead they were forecast at about 1.7. But this still had relatively little effect on total global population; the low-fertility nations are not typically the most populous ones.

Now, however, the U.N.’s new proposal acknowledges that fertility is falling more rapidly than expected in some big, less developed countries with “intermediate” levels of fertility (2.1 to 5.0). These include India, Pakistan, Indonesia, Brazil, Mexico, Egypt, Bangladesh and the Philippines. (China, at 1.8 is already below replacement level, in part due to coercive family planning policies.) The U.N. concludes that the less developed nations are heading toward a fertility rate of 1.85, down significantly from the 2.1 of earlier projections. This would yield a maximum global population in the 8 billion to 9 billion range.

I suspect that alarmists will be displeased by the new reality-based projections, seeing it as an attack on their rice bowl. They can take some succor from the to-ing and fro-ing within the document. While it states that the new medium projections will lead to “rates of population growth . . . much lower than currently projected,” it also notes that population will still be growing (slightly) by mid-century. Moreover, it states that those who have maintained that “the end of population growth” is in sight have been “somewhat hyperbolic.” But, as mentioned, the central word is “reductions,” which makes the mere “end” of population growth an overly cautious statement rather than hyperbolic.

Actually, I think even the new 1.85 figure is still too high, and that by 2050 we will see a substantial population decline. I believe the slow decline the document speaks of will snowball, as happens in exponential arithmetic.

What does it mean? Most important, that we are not a species that is out of control. The last half of the 20th century was a demographic wonderment, featuring both a population explosion (in developing countries) and a birth dearth (in developed countries) simultaneously. For a while the explosion was the biggest news. Now the dearth and subsequent depopulation should share the billing and soon move center stage.

This doesn’t mean we should pay less attention to family planning or environmental problems, but it does mean that those issues should be viewed calmly and without panic. The future remains a mystery. But inexorable population growth isn’t part of it.