In July 2008, the Center for a New American Security hosted an international climate change “war game,” a future scenario exercise to explore the national security implications of global climate change. Military organizations and businesses around the world have long used such exercises to anticipate developments and manage risk and uncertainty – and to test how plans, strategies, and ideas may hold up in a range of plausible futures. This working paper provides major findings from the war game, and background information on how CNAS developed the “2015 World” in which the scenario was set.