As roosters announce the dawn in this small farming village, the morning sun highlights a flock of sheep and filters through the smoke that billows from the adobe houses. The scene, repeated daily in thousands of hamlets throughout rural Latin America, can be as deadly as it is bucolic.

Burning biomass—wood, coal, animal dung or agricultural waste—indoors for cooking kills an estimated 2 million people worldwide annually, according to the World Health Organization (WHO). Besides causing health problems—from chronic obstructive pulmonary disease to cardiovascular disease—cooking smoke is a source of greenhouse gases and black carbon, which contribute to climate change.

Increasing concern about both the health and climate impacts of indoor air pollution has spurred campaigns to install cookstoves that are ostensibly cleaner. But recent studies indicate that fuel-efficient models do not necessarily lower health risks—and if poorly designed or installed, can actually increase harmful air emissions.