1. Harvard University, Resources for the Future, National Bureau of Economic Research, Center for Strategic and International Studies, 79 JFK Street, Mailbox 57, Cambridge, MA 02138, USA
2. Duke University, Resources for the Future, National Bureau of Economic Research, Center for Global Development, Box 90239, Durham, NC 27708, USA
3. Research Institute of Innovative Technology for the Earth, University of Tokyo, 9-2 Kizugawadi, Kizugawa-Shi, Kyoto 619-0292, Japan