Recent events have given reason to hope that a global agreement to limit greenhouse gas emissions is achievable. President Barack Obama announced a provisional target based on a bill that passed the House of Representatives in June (the Senate, unable to pass a counterpart, will resume consideration in the spring). The next day, China announced its own target.

Some doubt whether President Obama's announcement will carry much weight without legislation from Congress. And China's target disappointed many, as it ties emissions to economic growth; emissions will continue to increase, just not as fast.

But the provisional commitments at least bring the top two greenhouse gas-emitting countries to this week's climate conference in Denmark with a firm starting point. What's needed now is a new approach to the central challenge: convincing countries like China - facing major costs to implement emission reductions - to agree to an aggressive plan.

A strategy worth considering is to highlight ancillary benefits of emission caps that might drive consensus - benefits that we've largely neglected, being so accustomed to hearing about climate change-induced cataclysm. For the United States and some other countries, reducing dependence on foreign energy sources carries national security significance, and this issue is sometimes raised. But we almost never hear about the lives and health-related costs that cleaner air would save.

Besides emitting gases that drive climate change, coal-fired electricity plants and petroleum-burning vehicles release air pollutants that cause illness and death from respiratory and cardiovascular disease, among other conditions. This is often left out of the climate change-framed debate over greenhouse gas emissions, but the costs are substantial and not taken into account by market energy pricing.

In October, the National Academy of Sciences released a study showing that fossil fuel consumption costs the United States around $120 billion per year in air pollution-related health costs. The estimated number of U.S. deaths attributable to fossil fuel consumption each year - around 20,000 - is about the same as the number of homicides.

Worldwide, the countries responsible for the most greenhouse gas emissions are the ones with the most deaths from outdoor air pollution. China, which gets two-thirds of its energy from coal-fired plants, leads both lists, followed by the United States, Russia and India for emissions; and India, the United States, and Russia for air pollution deaths. The World Bank estimates the health-related costs of China's outdoor air pollution at 1.2 percent to 3.8 percent of its gross domestic product, comparable to what China says it spends on its military.

The agendas of climate change mitigation and air pollution reduction are sometimes, but not always, aligned. Reducing reliance on coal-fired power plants will serve both ends, and we've learned recently that carbon dioxide, responsible for the largest part of the greenhouse effect, may exacerbate the public health harm of other air pollutants (a Stanford study projected an additional 1,000 deaths each year in the United States from carbon-induced air pollution, beyond the deaths estimated with current air pollution models).

In other cases, there may be tension between the perspectives. For example, a study published in the journal Nature this year found that air pollution actually helps plants absorb carbon dioxide (the pollutant particles scatter sunlight to distant plants), so that reducing pollution might require larger emission cuts than suggested by current models. Replacing petroleum with diesel in automobiles would reduce carbon emissions but increase air pollution.

Perhaps the greatest concern among climate change mitigation advocates might be that acknowledging the ancillary benefits of improved air quality and the climate change trade-offs could distract from the high-profile global effort to reduce carbon emissions. This is understandable, and if world leaders were near consensus on a climate change agreement, it might be compelling. But they are not, and broadening the discussion to include benefits from cleaner air could help drive the reluctant toward agreement.

A 2009 study from the Organisation for Economic Co-operation and Development found that under a global plan to cut emissions in 2050 by 50 percent relative to 2005, China and India would not derive economic benefits from a stabilizing climate until well beyond 2050 - but they would reap benefits from improved air quality almost immediately. The costs of implementing policy to curb emissions were much higher in China and India than the 30 countries in the Organisation for Economic Co-operation and Development, but the economic benefits of less air pollution were much larger too.

This bears out the intuitive promise of bringing a clean-air perspective to the climate change agenda: Those facing the greatest near-term costs to implement emission reductions also have the most to gain from cleaner air.

Dr. Jean-Paul Chretien, who received his M.D. and PhD degrees from the Johns Hopkins University, is a fellow of the Truman National Security Project and an active duty U.S. military officer. His e-mail is

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