It appears increasingly likely that the U.S. will adopt a system of limited and transferable emission allowances (a cap-and-trade approach) to control greenhouse gas emissions. Robert Stavins, the environmental economist from Harvard's Kennedy School of Government, discusses the issues involved in in this working paper: Addressing Climate Change with a Comprehensive U.S. Cap-and-Trade System (AEI-Brookings Joint Center for Regulatory Studies, November 2007):