WASHINGTON — CAN the planet Earth, regions of which are already sagging under the weight of its 5 billion passengers, sustain 5 billion or 10 billion more?
By the conventional wisdom, the answer is a resounding no. A majority of demographers and environmentalists say the earth's soils, forests, and water resources are already being depleted at a dangerous rate. If population doubles or triples, they warn, the human load could produce an ecological nightmare.
But a sturdy group of demographic contrarians takes exception, scoffing at the notion that population growth will mortgage the world's future.
"Why should we worry?" asks Ben Wattenberg, a scholar at the American Enterprise Institute in Washington. "We've gone from 1 [billion] to 5 billion while living standards have gone up exponentially. There's no evidence that population growth diminishes or dilutes development."
The optimism of academics like Mr. Wattenberg is rooted in an array of hopeful statistics on rising incomes, food production, and literacy rates that seem to belie the notion that population growth breeds declining living standards and ecological overload. If population growth creates problems, they say, then history has proved time and again that it also calls forth the human ingenuity needed to solve them. Case in point: the green revolution.
"The track record of these kinds of extrapolative predictions is simply historically dismal," says Larry Summers, chief economist of the World Bank in Washington, referring to the forecasts of doomsayers. "1990 is as close to 1930 as it is to 2050. No one in 1930 predicted the green revolution, antibiotics, North Sea oil, or the environmental movement."
Demographers acknowledge that they have failed to anticipate such developments. But they say they also failed to anticipate global warming, ozone depletion, and deforestation, all attributed in part to population growth.
"It makes you wonder what else is going on out there that we don't know about yet," says Paul Erlich, author of the 1968 bestseller "The Population Bomb" (Ballantine).
The main locus of disagreement between mainstream demographers and some economists is whether the world will be able to feed billions more people.
The economists say that by using technology and management skills already available, farmers in Bangladesh can become as productive as farmers in Kansas.
Demographers say sweeping political and social changes will be required to make such technical possibilities a reality. They also note the thorn on the rose of the green revolution, that even as output is being increased, soils are being eroded, ground water polluted, and forest lands destroyed.
"In some areas agricultural production is stripping the resource base and the bank is going to run out soon," says agronomist Stephen Vosti.
One middle view is expressed by an agronomist, an official of the Rome-based Food and Agriculture Organization, a United Nations agency. "Expanding onto the limited remaining agricultural lands available and utilizing incremental improvements in technology, farmers in most parts of the world may be able to keep pace with population growth," he says.
But sub-Saharan Africa will lose the population race, producing a sustained crisis, he says. "We are talking about famines, severely aggravated by the collapse of civil order."
Where the more optimistic economists accent aggregate trends, demographers tend to focus on distribution. Statistics on per-capita increases in food production, for example, provide cold comfort to the billion or more people worldwide who now live on the edge of starvation, they say.
"We're seeing increased polarization of the world in terms of living standards, with a small fraction of the world living in affluence and most of the world living in poverty," says Robert Repetto of the World Resources Institute in Washington.
"More food is being raised now, but it does not feed hungry people more. It feeds more hungry people," adds Donella Meadows, a coauthor of "Beyond the Limits" (Chelsea Green).
Optimists say that the population bomb has been defused because fertility rates have plummeted in most parts of the world within one generation. They say improving economic conditions will make reductions to and even below replacement-level fertility faster and easier.
"Defense budgets are coming down, market economies are taking root, and democracy is spreading," says Wattenberg. "That's an enormous boon to economic development, and that's the key to lowering fertility rates."
"The fact remains, we're adding 100 million people to the world each year," responds Jane DeLung, president of the Population Resource Center in Princeton, N.J. "Technology has reduced the specter of mass famine, but it may not reduce the sheer impact of projected population growth if you're talking about quality of life."