1. U.S. Environmental Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC 20460, USA
2. Brookings Institution, 1775 Massachusetts Ave, NW Washington, DC 20036, USA
3. Joint Program on the Science and Policy of Global Change, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
4. Maxwell School, Syracuse University and Brookings, NY, USA