Over the last two decades, many experts have made urgent calls to take the global environment seriously as a national security problem. But the diffuse and remote nature of the threat has made it difficult to integrate planetary peril into traditional security thinking. This important volume, edited by a leading figure in the foreign policy establishment, makes an eloquent argument for why today's decision-makers have no choice but to act on the coming dangers of global climate change. According to Campbell, climate change is not just another problem to worry about: left unchecked, it will come to represent "perhaps the single greatest risk to our national security, even greater than terrorism, rogue states, the rise of China, or the proliferation of weapons of mass destruction." The historian J. R. McNeill offers a fascinating survey of past centuries of environmental upheaval. In other chapters, experts chart three alternative scenarios based on different projections of climate change and their implications for peace and stability. A cascade of unwelcome effects are identified: large-scale migrations, conflict over scarce resources, and the geopolitical reordering of states as they struggle to cope with coastal flooding, food shortages, and disease. In the most catastrophic scenario, political order in large parts of the developing world will collapse and hundreds of millions of people will perish or emigrate.