What would it cost to make such a big improvement? In many parts of the world, an effective, improved stove costing just $30 is all that is needed to reduce indoor air pollution dramatically. The price is higher in some parts because of particular needs; in China, heating is needed as well as cooking, so the cost of an effective, improved stove increases to somewhat over $100. Nevertheless, providing improved stoves for 50 percent of those cooking on unhealthy, smoky, traditional ones would cost about $5 billion a year.

So for every dollar spent on better stoves would do $10 worth of good. This gives us an excellent opportunity to compare this target for air pollution with all the other worthy targets proposed for the next 15 years.

However, helping 1.4 billion people with better stoves doesn't solve the problem. Another 1.4 billion are still cooking with traditional, polluting stoves, and even improved stoves cause more pollution than found in most cities. Besides, some of the smoke from these improved stoves reaches outside so there is pollution within the community as well.

A much cleaner solution is to get everyone to use gas. This would save 2.3 million deaths a year and avoid 13 billion days of illness, leading to more than twice the benefits. But unfortunately, gas stoves are more expensive and gas can cost about 200 dollars per household per year, so the costs are more than 10 times higher. Even so, for every dollar spent, we would get 2 dollars worth of benefits, a respectable, but not nearly as good a target. As the developing world gets richer, however, a move to gas and eventually electricity will be both affordable and have obvious health benefits.

The author is director of the Copenhagen Consensus Center.