Short goes so far as to call for a halt to future population growth. After all, the most profound way a U.S. citizen can impact climate change is to have fewer children, since every American child born today will add almost 10,000 metric tons of CO2 to the atmosphere under current conditions — five times more than a Chinese child and 160 times more than a baby from Bangladesh. Having one fewer child would reduce a family’s greenhouse gas impact 20 times more than driving a Toyota Prius, using Energy Star appliances and other environmentally friendly lifestyle choices combined, according to researchers at Oregon State University.

Eating Away

But the real problem today — as it has been since at least the time of Thomas Malthus — may be food. Simply to maintain today’s number of chronically malnourished or outright starving people — 1 billion — in 2050 with a larger population and present crop yields would require clearing 900 million additional hectares of land. At most, there are an additional 100 million hectares to add to the 4.3 billion already under cultivation worldwide, according to Pedro Sanchez, director of the Tropical Agriculture and the Rural Environment Program at the Earth Institute.

Concerns about population growth often boil down to concerns about too many of the wrong sort of people.

“Agriculture is the main driver of most ecological problems,” says economist Jeffrey Sachs, director of the Earth Institute at Columbia University. “We are literally eating away the other species on the planet.” After all, humans now directly employ some 40 percent of the total land area of Earth.

Nor can the solution be found in the ongoing increase in nature reserves, which currently cover some 15 million square kilometers of the planet. “There are desperately poor people surrounding many of these reserves,” Ehrlich says. “If I was there, I would shoot the hippo and eat it too.”

Concerns about population growth often boil down to concerns about too many of the wrong sort of people, as evidenced by recent efforts to tie environmental and anti-immigration efforts, such as an unsuccessful bid by nativist John Tanton to turn the Sierra Club against immigration. After all, governments from France to Australia pay their citizens to have babies in an effort to ward off the baby bust — and those efforts seem to be working. Women in developed countries are having more children again, according to demographer Mikko Myrskylä of the University of Pennsylvania. “Increases in development are likely to reverse fertility declines — even if we cannot expect fertility to rise again above replacement levels,” Myrskylä writes in Nature. “We expect countries at the most advanced development stages to face a relatively stable population size.”

That does not include immigration, of course, which some environmentalists decry as a threat to the sustainable future of the U.S. Yet the U.S. has only 80 people per square mile compared with 140 per square mile in Mexico, to take just one example. Immigration may actually reduce environmental pressures elsewhere — such as Haiti, where 760 people live for every square mile of countryside. And immigration remains the single most effective poverty alleviation program on the planet, according to economist Lant Pritchett of Harvard University. He argues that labor (i.e., people) should be as free to move internationally as capital (i.e., money).

It’s the Consumption, Stupid

194 lb.: The amount of stuff the average American uses per dayUltimately, the problem isn’t the number of people, necessarily. It’s what those people do. The average American (just one of 309 million) uses up some 194 pounds of stuff—food, water, plastics, metals and other things — per day, day in and day out. We consume a full 25 percent of the world’s energy despite representing just 5 percent of global population. And that consumerism is spreading, whether it be the adoption of cars as a lifestyle choice in China or gadget lust in the U.S.

“Consumerism is now spreading around the world,” says Erik Assadourian, a senior fellow at the Worldwatch Institute. “Is this going to keep spreading? Or are countries going to start recognizing that this is not a good path?”

What’s needed is the wholesale junking of the disposable life, Assadourian says, “a world where machismo is not connected to the size of a car but the fact that you don’t have one at all.” That may not be all our fault. “We are not stupid, we’re not ignorant, we don’t even necessarily have bad values with respect to the environment,” says political scientist Michael Maniates of Allegheny College. “We’re trying to do our best within cultural systems that elevate unsustainable choices.”

The world already grows enough food to feed 10 billion people — if we all ate a vegetarian diet, Cohen notes. Such lifestyle changes may prove unpalatable, transforming everything from how the dead get buried to gadgets that last a lifetime or more.

As simply put by the United Nations Millennium Ecosystem Assessment in 2005: “Human activity is putting such strain on the natural functions of Earth that the ability of the planet’s ecosystems to sustain future generations can no longer be taken for granted.” In other words, we just might let the world go to the dogs.  View Ensia homepage

This article originally appeared in the Summer 2010 issue of Momentum magazine, Ensia’s predecessor.