Global climate change poses not only environmental hazards but profound risks to planetary peace and stability as well. Climatic Cataclysm gathers experts on climate science, oceanography, history, political science, foreign policy, and national security to take the measure of these risks. The contributors have developed three scenarios of what the future may hold. The expected scenario relies on current scientific models to project the effects of climate change over the next 30 years. The severe scenario, which posits a much stronger climate response to current levels of carbon loading, foresees profound and potentially destabilizing global effects over the next generation or more. Finally, the catastrophic scenario is characterized by a devastating “tipping point” in the climate system, perhaps 50 or 100 years hence. In this future world, the land-based polar ice sheets have disappeared, global sea levels have risen dramatically, and the existing natural order has been destroyed beyond repair. The contributors analyze the security implications of these scenarios, which at a minimum include increased disease proliferation; tensions caused by large-scale migration; and conflict sparked by resource scarcity, particularly in Africa. They consider what we can learn from the experience of early civilizations confronted with natural disaster, and they ask what the three largest emitters of greenhouse gases—the United States, the European Union, and China—can do to reduce and manage future risks. In the coming decade, the United States faces an ominous set of foreign policy and national security challenges. Global climate change will not only complicate these tasks, but as this sobering study reveals, it may also create new challenges that dwarf those of today. Contributors include Leon Fuerth (George Washington University), Jay Gulledge (Pew Center on Global Climate Change), Alexander T. J. Lennon (Center for Strategic and International Studies), J.R. McNeill (Georgetown University), Derek Mix (Center for Strategic and International Studies), Peter Ogden (Center for American Progress), John Podesta (Center for American Progress), Julianne Smith (Center for Strategic and International Studies), Richard Weitz (Hudson Institute), and R. James Woolsey (Booz Allen Hamilton).