Millions of lives were at stake. Hillary Clinton was on board. Money poured in. And yet the big aims behind an effort to tackle the plague of third-world cooking fires has produced only modest gains.

For many decades, it was one of the globe’s most underappreciated health menaces:  household pollution in developing countries, much of it smoke from cooking fires.

The dangerous smoke — from wood, dung or charcoal fires used by 3 billion people in villages and slums across Africa, Central America and Asia — was estimated by health officials to shorten millions of lives every year. The World Health Organization in 2004 labeled household pollution, “The Killer in the Kitchen.” Women and children nearest the hearth paid the greatest price.

If the health costs were not ominous enough, many environmental advocates worried that what was known as “biomass” cooking also had potentially grave consequences for the planet’s climate.