Unexpected heat suppresses emigration from the world's poorest countries

Whether climate stress displaces people or traps them in place is unresolved. The common intuition is displacement: crops fail, heat becomes unliveable and people leave. Other work predicts the opposite for poor countries, where migration abroad is expensive and the shock that sharpens the wish to leave can destroy the means to go. Estimates disagree, partly because realized temperature mixes warming that households anticipated with warming they did not. I isolate the unanticipated part with temperature forecast errors, the warmth or cold a forecast missed, and estimate their effect on monthly international migration from countries holding most of the world’s population. Here I show that unexpected warmth does not detectably move migration on average, but that in low-income countries an unexpectedly hot month lowers departures over the following year. No richer income group shows a detectable response. The migration suppression is strongest where incomes depend on agriculture, also appears outside the growing season and leaves in-migration flat, consistent with heat removing the means to move. For the poorest countries, unexpected heat may hold people back rather than push them abroad. Projections and policies built around displacement may overstate departures from these countries and overlook those who cannot afford to leave.