Carbon Copies: The Population Factor in Climate Change

Robert Engelman

Nations don't burn fossil fuels; people do. But as Vice President Al Gore found out recently when conservatives blasted him for a comment made to a group of weather forecasters, combining the politics of population with those of global warming produces a highly combustible mixture. While few would argue that the atmosphere's changing composition has nothing to do with global population, the details of the connection or its potential implications are rarely tackled. For if there's any environmentally related topic more controversial than climate change, it may well be population.

In early October, President Clinton proposed establishing binding limits on U.S. greenhouse gas emissions, returning by around the year 2010 to the lower levels of 1990. Such a plan would elevate the importance of population as well as consumption in the global warming debate, for any limitation would apply no matter how fast U.S. population grows in the next decade and a half. Obviously, the more people, the less carbon-based fuel each person can burn.

Whether or not Clinton succeeds in convincing Congress to go along with his proposal, there is good reason to consider the population-climate link. Both issues matter immensely to humanity's future, and actions taken over the next few years will influence demographic and climatic trends well into the next millennium. While surging economic growth and fuel consumption make emissions reductions look painfully difficult, demographic trends are much more positive: World population growth is now slowing down faster than demographers expected just a few years ago, due largely to declines in desired family size and improved access to family planning services. Continuation of this trend, however, will require sustained support from societies and governments that is not at all certain today: Our own Congress, ironically, has cut its financial support for international family efforts by a third since 1995.

In considering population and climate, we confront as well the issue of unequal individual consumption around the world of petroleum, coal and natural gas, the combustion of which releases carbon dioxide (CO2) and other greenhouse gases. With less than 5 percent of the world's population, the United States produces nearly a quarter of global greenhouse emissions. Both Clinton and his political opponents now insist that developing countries commit to limiting their own emissions of greenhouse gases before the United States does the same. But it is hard to imagine developing countries agreeing to freeze their own emissions at per capita levels that are a small fraction of those in the United States.

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When it comes to fossil fuels, Americans burn just about the most of all. On average, each of us sends more than 20 metric tons of carbon dioxide into the air each year. The average person on the planet, by contrast, produces just over four tons annually, and the average resident of dozens of African and Asian countries produces less than a ton.

Thus it's easy to understand why developing countries want industrialized countries to make the first move to slow global warming. What's harder to understand is how developing countries could make the next move--unless a plan emerges that would somehow reward them for continuing their currently low levels of per capita emissions.

The fact remains, however, that the atmosphere may be literally as big as all outdoors, but it's still the equivalent of a closed room full of smokers once the climate problem is recognized. The more smokers, the less room for the smoke--or greenhouse gases--each one exhales.

The increase of the world's population from a few million human beings in prehistoric times to nearly six billion today goes a long way toward explaining how human activities have now become so significant they influence climate. One could argue that the industrial revolution, stoked since the mid-18th century by King Carbon, played a larger role, but consider: Had the world's population stabilized around the year 5000 B.C. at its then-current size of around 20 million, each one of us would have to burn 600 times more fossil fuel per day than the typical U.S. resident in order to alter the global atmosphere as dramatically as today's population of 5.9 billion is doing. With only 20 million of us, we could each fly a supersonic airplane to work each morning without making things worse than they are right now.

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While more fantasy than science fiction, the supersonic scenario does illustrate that the difficulty of reducing total global greenhouse gas emissions increases in proportion to how rapidly and how long global population continues to grow. In the United States, carbon dioxide combustion grew by 1.4 percent annually between 1990 and 1996, according to new figures released by the Department of Energy. Of this, only 0.4 percent was attributed to increased per capita fuel consumption. The remaining two-thirds of U.S. emissions growth came from the growth in the country's population.

Our 1-percent rate of annual growth--low by global standards but high in comparison with Europe and Japan--may help explain why the governments in those countries are more ambitious than the Clinton Administration in the proposals they bring to Kyoto, Japan, where negotiations proceed in early December on a binding emissions limit for industrialized countries. Populations in Japan and in most of Europe are roughly stable. When a country with no population growth freezes its greenhouse gas emissions, all it has to do is keep each person's fossil-fuel use on an even keel. For the United States, which adds about 2.6 million people each year, any freeze in emissions means a perpetual squeeze on a per capita basis until population size stabilizes, which it shows no signs of doing soon.

Based on current U.S. Census Bureau projections, this country's population will grow from today's 268 million people to somewhere between 281 million and 315 million people in the year 2010, the year in which Clinton hopes the nation will be back at 1990 level emissions. The President argues that these relatively modest emissions reductions will require no sacrifice in economic growth or lifestyle, and he may be right. But it's worth noting that under the Census Bureau's low population growth scenario, per capita emissions would need to shrink 1 percent a year on average through 2010 to achieve Clinton's target, while under the high scenario the squeeze will amount to 2 percent a year. If greater energy efficiency and a move toward more use of renewable energy sources can accomplish a 1 percent emissions reduction per person per year--but no more than that--then the rate of population growth will make the difference between a greenhouse-gas technological fix and lifestyle sacrifices by U.S. citizens.

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