Global climate changes caused by human activities have the potential to alter agricultural productivity, freshwater availability and quality, sea level, and many other factors of importance to society. Although the principal responsibility for the production of greenhouse gases lies with the industrialized countries, some of the worst impacts will fall on developing countries least able to prevent or adapt to the changes. This characteristic, together with the long history of political frictions and disputes worsened by environmental stresses suggests that global climatic changes have the potential to exacerbate existing international tensions. Severe risks facing developing nations from rapid climatic changes are discussed here together with actions that both the industrialized and developing world can take to prevent or mitigate the worst effects. The world is already committed to some climatic changes because of gases emitted over the last century. Slowing the rate of future change can increase the time available to understand and prevent the worst impacts and reduce the risks of international disputes and conflicts.