A major international assessment released in 2007 concluded that the Earth's climate had warmed unequivocally over the past century, and that elevated levels of so-called "greenhouse gases" (GHG) were likely responsible for a major portion of the observed warming. Contentious debates scrutinise issues of science, economics, values, geopolitics and a host of other concerns. Deliberations also weigh the appropriateness of alternative policy tools and program designs. The economic stakes are potentially large, with both the costs of controls and the "costs of inaction" ranging, by some estimates, into trillions of dollars over several decades. This book explores the varied current issues and policy tools relating to climate change.