Carbon Copies: The Population Factor in Climate Change

Robert Engelman

When one moves to the international arena, this type of per-capita calculation is complicated by starkly unequal use of fossil fuel from country to country. The national populations that are growing the fastest, in fact, are precisely those contributing the least on a per-capita basis to the greenhouse problem. Emissions inequality reflects income inequality.

The easy generalization is that consumption in wealthy countries matters far more than population growth in the poor countries. The problem with this generalization is that both population and per-capita fossil-fuel consumption are growing in both rich and poor countries. It's also the case that today's population growth fuels future increases in emissions.

At least one billion of the world's people could argue today that they are not contributing to climate change at all, since their modest per capita greenhouse-gas emissions, if emulated by everyone else in the world, would result in stable or even falling greenhouse gas concentrations in the atmosphere. This population is growing rapidly, however, and in escaping poverty their descendants' greenhouse gas emissions are likely to come closer to the global average and be less sustaining of the global climate. And the more people, the lower will be the per capita emission of carbon dioxide and other gases that will be consistent with a stable atmosphere and thus a stable climate.

If each person on the planet were endowed at birth with the kind of "tradable emissions permit" that the Clinton administration is considering for U.S. companies, the annual endowment would presently allow for the amount of fossil fuel that the average American burns in just 11 weeks. And that assumes only an effort to return to 1990 levels of greenhouse-gas emissions, despite the fact that such emissions levels would continue to push global temperatures higher for decades to come. If the goal were actually to stabilize the atmosphere and climate, the annual global "stable-climate" endowment of per capita greenhouse-gas emissions would be much less generous: about equivalent to three weeks of the American lifestyle.

But even these dauntingly stingy emissions allowances are based on today's world population. Should human numbers double to 11.8 billion, as demographers still consider quite plausible, the emissions endowments would need to be cut in half. Each person would start contributing to further global warming after the equivalent of 10 days of the current American lifestyle.

Thus the size of global population will have everything to do with how much global per capita emission levels will need to decline to avoid further climate change. Rich and poor alike will be better off with a relatively smaller and slower growing population than with a relatively larger and more rapidly growing one.

The good news is that world population growth is slowing down. Today's population adds a bit more than 80 million people each year--an annual population increment that is beginning to shrink for the first time in many years.

The number of births per woman on average is probably lower today than at any other period of human history, thanks in large part to changing ideals about family size, improved educational and economic opportunities for girls and women, and--critically--greater access to family planning services in most of the world's nations. If governments and others seize the chance to expand such opportunities and services--a big if--it is possible that human numbers will never double from current levels. Population could stabilize at fewer than 8 billion before the middle of the 21st century.

This demographic revolution appears to be well-timed to address human-induced climate change, which under most scientific scenarios will by the year 2050 be obvious and quite possibly disruptive. And it is a revolution we have much more experience supporting than we do attempts to slow future climate change. Thirty-five years of efforts in the family planning and development fields make clear that the best policies are those that help provide people what they want anyway: the ability to time pregnancies and space births, a decent education, and opportunities to work for a fair and reasonable wage. Indeed, the desire for small families and later childbearing is now so widespread in most of the world that an effective population strategy today can in large part be to simply respond to this rising demand with effective, high-quality reproductive health services.

There is no basis for any argument that slowing population growth can "cure" global warming. Nonetheless, relatively simple and affordable steps that can be taken today to expand access to family planning services and raise the status of women can indeed play a role in protecting the global climate. Such steps are only a part of what will be needed, but they are essential to long term climatic as well as demographic stability.

Access to good quality reproductive health services--as well as better education for girls and economic opportunities for women--make sense for humanitarian reasons that have nothing to do with population trends, let alone the hazards of global warming. Unfortunately, many members of Congress are hostile to the idea of making family planning services more widely accessible at home or abroad and are dubious that either population or climate change are worth worrying about.

They are. Both issues carry uncertain but serious and growing risks on a global scale, and neither is likely to disappear. The world is becoming more complex, and many of its problems are increasingly intertwined. Addressing human-induced climate change in the near term will require strong commitments around the world to wring out wasteful energy use and begin the inevitable shift toward carbon-free fuel sources.

In the long run, however, achieving a more stable climate than we have today will require a relatively stable atmosphere and that will require a stable population. And it may make a world of difference whether countries representing 8 billion or 12 billion human beings are struggling to find equitable and manageable ways to keep a lid on greenhouse-gas emissions. The good news is that we appear to be on the way to the former figure rather than the latter--if politicians don't sabotage the family planning services that provide the underpinnings for healthy childbearing and smaller families around the world.