Daniel Engber was online Sept. 13 to chat with readers about this article. Read the transcript.
What about the global picture—do we know how much population growth will contribute to climate change over the next 100 years? According to U.N. projections, the world population is likely to increase by 2.5 billion people—to a total of 9.2 billion—by the year 2050. That won't necessarily drive an equivalent percent increase in CO2 emissions, since most of the growth will be confined to the developing world, where per capita emissions are at their lowest. But we can also expect to see significant growth in the United States, where individuals do the most damage to the environment.
Overall, the increase in population over the next century won't matter quite as much for climate change as the increase in global wealth, but it's still important. In general, a country's per-capita emissions rise as it becomes more prosperous, while its fertility rate declines. In other words, fewer babies are born, but each one emits more CO2. (That's why the economic boom in China will create a massive increase in greenhouse gas emissions even if its population remains stable.) In fact, the birth of every additional child in the developed world can have a major impact on the cost of keeping global warming in check. According to studies published over the last decade, this amounts to as much as $10,000 to $20,000 per baby. Policies that promote family planning—in the United States or elsewhere—might well be more efficient than other means to reduce CO2 emissions, like a Kyoto-inspired carbon tax.
Despite these findings, Earth-advocacy groups almost never raise the issue of family size, focusing instead on lifestyle choices with more modest environmental rewards. When a group of population-control advocates tried to take control of the Sierra Club in 2004, their anti-immigration policies were decried as racist and they were voted down. (Most of the population growth in the United States comes from immigrants, who are likely to broaden their carbon footprint once they've arrived.) Even the academics on the Intergovernmental Panel on Climate Change have shied away from direct references to population and global warming.
They have good reason to be squeamish. The anti-life implications of Weisman's book are likely to alienate some moderates, as well as any social conservatives who might otherwise be drifting green. There's already been a strong Christian backlash against the GOP defectors of the "Creation Care" movement, with their solar-powered churches and prayers over global warming. Right-wing religious groups accuse the evangelical environmentalists of being in league with tree-hugging abortionists.
Worries over population growth also give fodder to the climate-change skeptics, who are quick to reminisce over the ill-fated doomsday projections of Paul Ehrlich's The Population Bomb. Published in 1968 (just six years after Rachel Carson's Silent Spring), the book cited hockey-stick reproduction rates since the Industrial Revolution to predict an imminent global catastrophe. But dramatic improvements in agricultural technology provided enough food to forestall the crisis, and Ehrlich and his fellow Malthusians were discredited. To bring up overpopulation once again—now in the context of global warming rather than food shortages—invites the same counterargument: Science and innovation will save the day.
As a global solution for climate change, Weisman's depopulation plan may not have much of a chance. ("I knew in advance that I would touch some people's sensitive spots by bringing up the population issue," Weisman told Washington Post readers in an online chat, "but I did so because it's been missing too long from the discussion.") But that's no reason to neglect birth rates from the personal calculus of living green. With the rise of consumer-driven environmentalism, it may be that the McKibben moment has finally arrived. Whether it's eating vegetarian or wearing organic eye shadow, we're all shopping for absolution. We know that babies add more to global warming than anything else in our home. Isn't it time to cut back?