Throughout the Sahel, the region that stretches across Africa below the Sahara Desert, climate change is raising temperatures, increasing droughts and making rainfall less predictable, researchers say. These changes, in turn, are helping fuel Boko Haram, an Islamist extremist movement born in the 2000s in northern Nigeria out of political grievances, and stoking its violence, according to interviews with former militants, local leaders, military officials and researchers.

Climate change, they say, is reducing the economic prospects of young men in this part of Africa and making them more susceptible to recruitment by violent extremists. This dynamic reflects a broader finding by the United Nations this year that the opportunity for jobs, rather than religious ideology, is the main reason that people join extremist groups across Africa.

Local residents and researchers say that climate change also fosters conflict in the Lake Chad region, as extreme hunger pushes people to begin fishing and farming in areas controlled by extremists. The Lake Chad area — where the borders of Chad, Nigeria, Cameroon and Niger converge — has provided bases for Boko Haram and other militant groups since 2014.

Military officials at the U.S. Africa Command said they view climate change as a “threat exacerbator” in the Lake Chad region and elsewhere. They said they are closely studying the connections between climate and conflict, because Africom’s area of responsibility involves some of the Sahelian countries most vulnerable to climate change, including Mali and Burkina Faso, where Islamist violence is spiraling. An official in the French military, which has one of its largest African bases in Chad, agreed that climate change contributes to the conflict.

Photographed for The Washington Post

With journalist Rachel Chason and photo editor Olivier Laurent