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E & E News, October 12, 2010

Slowing population growth could reduce projected greenhouse gas emissions
By Lauren Morello

Slowing population growth could provide up to a third of the greenhouse gas emissions cuts needed to avoid dangerous climate change, a new study suggests.

The world's population now stands at 6.9 billion, and the United Nations estimates it could swell to 9 billion by the middle of the century. Slowing that growth could provide major climate dividends, according to the new study, which appears in the latest edition of the Proceedings of the National Academy of Sciences.

"We find that, in general, different demographic futures make a really big difference to emissions by the end of the century, a very clear and large effect in the long term," said lead author Brian O'Neill, a climate scientist at the National Center for Atmospheric Research. "In the short term, it's a smaller effect -- but one that's still significant."

Holding the global population to 7.4 billion in 2050 could reduce the world's output of heat-trapping carbon dioxide by 1.4 billion to 2.5 billion metric tons.

That's equivalent to 16 to 29 percent of the emissions cuts scientists believe are needed to limit warming to 2 degrees Celsius above preindustrial levels.

But it's not just the number of people that matters, according to the new study, which also examined how aging, urbanization and changes in household size would affect the world's greenhouse gas emissions.

Overall population size had the most influence on future emissions, the analysis found, but urbanization -- which tends to drive emissions higher -- also played a significant role.

That's a key finding, O'Neill said, because urbanization "is happening now, and changes will be occurring over the next few decades -- it's not an effect that shows up a hundred years from now."

Aging and urbanization are also factors

Take China, which is now about 40 percent urban.

"Whether it reaches 80 percent urban in 30 years versus 50 or 60 years is really going to make a big difference to energy demand and greenhouse gas emissions," O'Neill said.

But the effect isn't universal. It's most pronounced in developing countries, where there's a bigger disparity between rural and urban lifestyles -- and where urbanization means not just a population influx for cities but a shift in the types of industries driving the national economy.

Graying populations will help reduce emissions to some extent in coming decades, the study finds, but the effect is outweighed by emissions gains produced by population growth and urbanization.

O'Neill and his colleagues recommend that policymakers seeking to slow climate change focus on slowing population growth, rather than crafting policies to influence aging or urbanization trends.

They say that meeting existing demand for family planning services in the United States and developing countries -- minus China, which has long had a one-child-per-family policy -- could provide half the emissions reductions expected under the lower population growth scenario outlined in the study.

That's a rough estimate to "give a sense of what kinds of policies are usually discussed or are on the table" in discussions about limiting population growth, O'Neill said.

Consumption drives up China's emissions

David Satterthwaite, a senior fellow at the International Institute for Environment and Development in London, said he thought the new study correctly identified a "large, unmet need for sexual and reproductive health services" and the effect slowing population growth could have on greenhouse gas emissions.

Still, Satterthwaite said he believes that consumption is an even bigger driver of greenhouse gas emissions.

"It's actually in the mostly in the wealthy nations that you've had enormous increases in greenhouse gas emissions, even though population hasn't grown very much," he said.

China, where the population growth rate is small, has seen "one of the most dramatic" increases in emissions, he said. "In a sense, it's a reminder that population growth wasn't driving emissions -- it was the success of the Chinese economy that was driving emissions."

Economic success often reduces fertility rates in a given country, but "if all of them want to consume like Donald Trump, we're stuffed -- it's the consumption levels that worry me," Satterthwaite added.

But Kathleen Mogelgaard, senior adviser for population, gender and climate for Population Action International, said the study confirms "an intuitive sense" of the link between population growth and climate change.

Growth limits are a tough sell

"It's no-brainer that a world of 11 billion in 2050 will have a harder time coping with climate change than a world of 8 billion," she said. But past emissions scenarios have treated population simplistically or ignored the issue, she said.

"This study provides an empirical and powerful rationale for mobilizing resources to achieve universal access to family planning," Mogelgaard added.

But experts who favor policies to limit population growth say they are often a tough sell.

"Any talk about numbers is now unfortunately seen as coercive," said Fred Meyerson, an ecologist and demographer at the University of Rhode Island who has served on the boards of Planned Parenthood Federation of America and the Guttmacher Institute. "Relating population and environment has been attacked by both the right and left."

At the same time, he said, "we could be doing a lot better than we are in terms of slowing population growth" -- a statement directed at not just developing nations like India and China, but the United States.

"About half of U.S. pregnancies are unintended," Meyerson said. "In the Netherlands, it's only about 15 percent."

Mogelgaard is more optimistic.

"With the realization that climate change is such an immense problem that's going to require action in every sector, we're beginning to see a greater willingness to entertain the policy interventions in social sectors" -- like family planning -- "that are going to have an impact on emissions," she said.

Copyright 2010 E&E Publishing.

Photo © Paul S. Hamilton