The United States has joined with other nations to express concern about climate change. In the absence of a comprehensive policy direction, technological advances are creating alternatives to the traditional approaches to climate change (mitigation and adaptation). If deployed, these new technologies could modify the Earth's climate on a large scale. The term "geoengineering" describes this array of technologies that aim, through large-scale and deliberate modifications of the Earth's energy balance, to reduce temperatures and counteract anthropogenic climate change. Most of these technologies are at the conceptual and research stages, and their effectiveness at reducing global temperatures has yet to be proven. This book addresses the possibility of geoengineering technologies which may warrant policymakers attention at the federal and international levels.