The "birth dearth": when it comes to analyzing world population, it's a numbers game.

It's easy enough to make the world population explosion go away: Start with the "birth dearth" that could cause Europe to lose 24 percent of its population by 2060, and cut Japan's in half by 2100. In England, women have an average of 1.7 children, below replacement level. In Spain, the fertility rate is 1.15--the lowest rate in the world. Stir in the fact that the United Nations (UN) recently revised a minor course correction in its population projections, finding that AIDS and declining fertility rates in the Third World will lead to 400 million fewer people sharing the planet by 2050.

The usual suspects are seizing on the information and declaring the population crisis over and its major voices discredited. "The idea that unbridled population growth will lead to environmental and social disasters as the world meets its 'carrying capacity' is a holy canon of the environmental movement," read an editorial in the Orange County Register. "Yet increasing evidence ... is painting a starkly different picture." The anti-abortion Center for Bio-Ethical Reform claims that the news from Europe proves Population Bomb author Paul Ehrlich to be "almost comically wrong." Ben Wattenberg, the commentator and TV host who coined the phrase "birth dearth," says "the next crisis is depopulation."

But the declining population problem is localized, not global. World population will continue to rise dramatically before it levels off. It is now more than 6.2 billion and continuing to grow by 77 million a year, equivalent to the combined 2001 populations of Mozambique, Paraguay, Poland, Portugal and Singapore. By 2050, according to the middle range of UN estimates, nine billion people will be sharing the planet--nearly 50 percent more than today.

Carl Haub, a demographer with the Population Reference Bureau, points out that the population explosion concern in the 1960s never had anything to do with the developed countries. "To conclude that we don't have a problem because of the 'birth dearth' is not addressing the issue at all. It's a straw man," he says. In fact, says Haub, it is by no means certain that the assumptions of the UN's nine billion projection will actually be realized. The actual numbers could be far higher.

"The UN Population Division assumes that the developing countries, in the long, long run, will emulate the declining fertility and the two-child families of the rest of the world," he says. "That rate will yield nine billion people by 2050, but if the actual numbers are only half a child more than that, population goes up to 20 billion and keeps on going."

John Bongaarts, a vice president of the Population Council, has conducted scientific studies of fertility in the developing world, and he agrees with Haub. "It is highly unlikely," he says, "that developing countries will converge on replacement fertility of 2.1 children per woman as is often assumed in population projections." The evidence, he says, suggests that "a significant number of countries will likely stall above 2.1 for periods of up to decades or will approach low fertility at a very slow pace."

Bongaarts and other analysts do envision permanent and worldwide population declines ahead, but it's unclear when some regions will make the transition to replacement-level fertility. Sub-Saharan Africa, for instance, has the highest fertility in the world, with rates above 5.0 in a majority of nations (and 7.2 in Niger), and Bongaarts sees "little change in reproductive behavior" there.

Chinas fertility rate of 1.7 certainly brings it within UN projections, but India (with a fertility rate of 3.4) is more problematic. It's far from clear where fertility in India is going. As an example, the Indian state of Uttar Pradesh has 170 million people, which would make it one of the largest countries in the world. Women in Uttar Pradesh have an average of five children each, but education and other factors could bring that number down dramatically. "What happens over the next 20 years in the developing countries will tell us what the total numbers are really going to be," Haub says.

Also worth considering is household size. Paul Ehrlich notes that even in places where population has declined, the number of households has grown. Household dynamics, he says, influences per-capita consumption "and thus biodiversity, through, for example, consumption of wood for fuel, habitat alteration for home building and associated activities, and greenhouse gas emissions."

The growth of households is especially noticeable in "biodiversity hotspots" around the world that are most affected by consumption increases, Ehrlich says. Ten percent of world plant species and seven percent of world animal species are now threatened, with loss of habitat a major factor. As Population Action International reports, "1.1 billion people live in the areas richest in species diversity and the most threatened by human activities."

"In thinking about the numbers we need to admit that there are several places on the planet that are already exceeding their carrying capacity," says David Ray, associate director of the Federation for American Immigration Reform (FAIR). An analysis of the planet's carrying capacity by Mathis Wackernagel of Redefining Progress estimates that we have exceeded the limits by 20 percent already.

In the U.S., population would have stabilized at replacement level if it weren't for record high legal immigration levels of one million new people per year. Because of those high levels, the U.S. could have more than 500 million people by 2100. Several observers have pointed out that the countries that provide the largest number of emigrants are not those affected by birth declines. According to Diana Hull, president of Californians for Population Stabilization (CAPS), the largest sending country, Mexico, has a fertility rate above 3.0, with its population set to double in 32 years. The fertility numbers in Asia are also high.

The "birth dearth" is certainly real, and cause for concern in the industrialized countries where it is occurring. But it's no reason for the world's population control movement to close up shop. Human population growth, say many experts, remains the single biggest cause of environmental degradation. CONTACT: Population Action International, [phone], www.populationaction.org; Population Council, [phone], www.popcouncil.org; Population Reference Bureau, [phone], www.prb.org.