When large numbers of asylum seekers and other migrants arrive at the borders of Western countries without prior authorization to enter, they are often treated as “spontaneous” arrivals. But migration is almost never truly spontaneous. Usually, human mobility across international borders is the result of complicated decision-making and a careful weighing of the costs and benefits. This episode features David Leblang, a professor of politics and public policy at the University of Virginia, who discusses how climate change fits into the migration calculus.