1. Nicholas School of the Environment, Duke University, Durham, North Carolina 27708;
2. Duke University Energy Initiative, Duke University, Durham, North Carolina 27708;
3. National Bureau of Economic Research, Cambridge, Massachusetts 02138
4. Sanford School of Public Policy and Nicholas Institute for Environmental Policy Solutions, Duke University, Durham, North Carolina 27708;
5. Resources for the Future, Washington, DC 20036
6. Center for Global Development, Washington, DC 20036