TOLIARA, Madagascar — When Julien Andrianiana started selling charcoal 14 years ago, he was just one of a few dealers around. Most households in Toliara, a coastal city in southwestern Madagascar, still used firewood for cooking.

As the city’s population doubled, business became so brisk that he managed to send two of his children to college, “thanks to charcoal.” It quickly became the product of choice in kitchens not only in Toliara, but also in other fast-growing cities across Africa.

Charcoal — cleaner and easier to use than firewood, cheaper and more readily available than gas or electricity — has become one of the biggest engines of Africa’s informal economy. But it has also become one of the greatest threats to its environment.

In Madagascar, an island nation off the eastern African coast and one of the world’s richest nations in biodiversity, the booming charcoal business is contributing to deforestation. It is expected to exacerbate the effects of climate change, which has already disrupted farming, fueled a migration to cities, and pushed many rural residents into the one thriving business left: charcoal.