In 2005, a hurricane named Katrina hit the states of Louisiana and Mississippi in the US, destroying properties and flooding areas. Many people left the region and still have not returned. While some of these people may eventually return, some may not, becoming migrants. Assuming this phenomenon will occur, is it unique? What is the role of the environment in migration? Can there be violent conflict between such migrants and residents in areas absorbing migrants? We evaluate these questions in the cases of Hurricane Katrina, the US Dust Bowl in the 1930s, and Bangladesh since the 1950s, demonstrating that environmental change can trigger large out-migration, which can cause violent conflict in areas receiving migrants. These findings have important policy implications. Climate change is expected to degrade the environment considerably in this century. Minimizing climate change-induced migration and violent conflict in receiving areas requires an engineered economic slowdown in the developed countries, and population stabilization and economic growth in the developing countries financed by the developed countries.