It was Woré Gana Seck who first told me about what she called the “climate refugees.”

Last fall I traveled with Seck, executive director of Green Senegal, on a US speaking tour about the effects of climate change on poor communities. At venues across the American Midwest, Seck told the stories of families split apart by drought and crop failure, of teenagers lost at sea while attempting dangerous ocean crossings. She talked about a certain cemetery in Spain–the “Cemetery of the Unknown People”–filled with West Africans who had fled their homelands seeking a better way to earn a living.

I thought of Seck last week when I read Lisa Friedman’s article Coming Soon: Mass Migrations Spurred by Climate Change. Friedman interviews a married couple in Haringar, Bangladesh, who are the last remaining members of their family in their village; everyone else has fled to India, unable to catch enough fish to earn a living because of increasingly severe cyclones and floods. One by one, Friedman says, small migrations like these are “changing the face of the world”:

Experts estimate that as many as 250 million people — a population almost that of the entire United States — could be on the move by 2050. They will go because temperatures are rising and desertification has set in where rainfall is needed most. They will go because more potent monsoons are making flood-prone areas worse. They will go because of other water events caused by melting glaciers, rising seas and the slow and deadly seepage of saline water into their wells and fields.

Friedman says these climate change-based migrations usually follow a certain pattern: First, people flee from rural villages to cities, seeking a way to earn a living that’s not tied to the land and the unpredictable weather. Then, when cities become overcrowded, they cross national borders–spurring potential conflicts as more people compete for resources on the same turf.

Seck described the same pattern when I interviewed her during the speaking tour. In this short excerpt, she explains why climate change drives young people in Senegal to flee their homes, and where they’re going:

Listening to Seck’s voice now, I remember the power of her words, and her ability to move her listeners here in the US. As the crisis grows more urgent, I hope stories like hers–and Friedman’s story of the family in Bangladesh–will continue to reach us.