In Africa, Lifting the Pall of Smoke From Cooking

"If you promote fuel switching, then not only are you going to have health benefits, you are going to have these global benefits," Bailis said.

He acknowledged that talk of nonrenewable oil-based fuels "raises a greenhouse-gas flag," because emissions from fossil fuels are responsible for the majority of greenhouse gases believed to contribute to global warming.

But more immediate obstacles prevent Africans from seeking alternative cooking fuels.

Africa's limited infrastructure for distilling and transporting fossil fuels is one of them, the study found.

But Robert J. van der Plas, an energy consultant in the Netherlands, disagreed. In a review of the Bailis team's study, he wrote that "kerosene is available in every nook and cranny of the urban and rural environment" in Africa.

The real problem, he noted in a study of energy use in Chad published earlier this year, is money. "A household would have to at least double its cooking fuel budget to switch to modern fuels, and there are not many households willing -- or able -- to do this."

As long as a switch to petroleum-based fuels is out of reach economically, Bailis and his team believe that in sub-Saharan Africa, the next best approach would be to switch to charcoal. It offers twice as much energy per unit of weight, Bailis said. It resists rot, termites will not eat it, "and compared to wood, it's fairly clean-burning."

Depending on how quickly the transition took place, the researchers said, using charcoal could prevent 1 million to 2.8 million premature deaths.

Switching from wood to charcoal, however, raises another set of issues.

To make charcoal, one or two men usually cut down a tree, light it, cover it with dirt and wait a few days for the end product -- a method that creates significant air pollution. However, if you "increase the efficiency of charcoal-making, you can improve health without having large environmental consequences," said Ezzati, an assistant professor at Harvard's School of Public Health.

Bailis also acknowledged that wider use of charcoal would do little to reduce deforestation. "We want the people who make these policies . . . to think about what kind of land-management policies can be put in place . . . for sustainable energy," he said.

WHO points out that reducing indoor air pollution would make progress toward at least half of the millennium development goals for improving the health and welfare of poor people everywhere, which each United Nations member pledged to reach by 2015. The less time women spend collecting fuel, the more time they have for education or careers, thus fighting poverty and promoting gender equality. The less smoke children breathe, the more likely they are to live to adulthood.

Success could raise the pall from millions.