Most of this population shift will take place in Sub-Saharan Africa, South Asia, and Latin America—three “hot spots” that represent 55 percent of the developing world’s populations.

This worst-case scenario is part of a ground-breaking study focused on the impacts of slow-onset climate, as opposed to more visibly dramatic events such as extreme storms and flooding. The report, Groundswell—Preparing for Internal Climate Migration, also shifts the focus from cross-border migration, which has drawn global attention as refugees and migrants flee war, poverty and oppression, to in-country migration, which involves many more millions of people on the move in search of viable places to live. The 143 million represent 2.8 percent of the three regions’ population.

Sea-level rise is already prompting the migration