Federal policymakers have long been concerned about the impact of manmade carbon dioxide (CO2) emissions on global climate change. To address these concerns, Congress has been debating a range of potential initiatives for reducing atmostpheric CO2 from U.S. sources. Legislative proposals would seek to limit U.S. CO2 emissions to specific (historical) levels through emissions caps, carbon taxes, or other regulatory mechanisms. Many of these proposals dictate or anticipate a declining long-term trajectory for annual U.S. carbon emissions. The most prominent CO2 proposals seek reductions of nationwide CO2 emissions to 1990 levels or lower by 2030. This book examines key uncertainties associated with CO2 emissions abatement measures, with a focus on available and emerging technologies, and new source review permits.