A scientific consensus is emerging that rising atmospheric concentrations of greenhouse gases are gradually changing the Earth's climate, although the magnitude, timing, and effects of the alteration remain very uncertain. The prospect of long-term climate change raises a variety of domestic and international economic policy issues on which there is little accord. Considerable disagreement exists about whether to control greenhouse gas emissions, and if so, how and by how much; and whether to coordinate climate-related policies at the international level, and if so, through what mechanisms. This Congressional Budget Office (CBO) study presents an overview of issues related to climate change, focusing primarily on its economic aspects. The study draws from numerous published sources to summarize the current state of climate science and provide a conceptual framework for addressing climate change as an economic problem. It also examines public policy options and discusses the potential complications and benefits of international coordination. In keeping with CBO's mandate to provide impartial analysis, the study makes no recommendations.