We poorly understand the ways in which multiple complex, coincident, and interacting environmental changes will alter habitability and drive population displacement, but these changes are likely to be associated with large burdens of disease and disability. Little is currently understood about how the combination of climatic disruption, natural hazards (e.g., droughts, heat waves, floods, fires, tropical storms), water scarcity, land degradation, and resulting crop and livestock failures may interact to make parts of the world that currently support large numbers of people uninhabitable. How many people are likely to be displaced? What populations are most vulnerable? And when people are displaced (many of them with very few resources) into areas where they may not be welcome, will civil strife ensue? We know that such displacement is associated with sharp increases in infectious disease outbreaks, malnutrition, and physical and mental trauma. What are the best approaches to managing increasing requirements for population movement with the least conflict and health burden? These types of questions require urgent focus.