The complex, contradictory and heartbreaking process of American climate migration is underway.

Another great American migration is now underway, this time forced by the warming that is altering how and where people can live. For now, it’s just a trickle. But in the corners of the country’s most vulnerable landscapes — on the shores of its sinking bayous and on the eroding bluffs of its coastal defenses — populations are already in disarray.