1. Environmental Science and Policy Program, Smith College, 44 College Lane, Northampton, MA 01063, USA
2. U.S. Environmental Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC 20460, USA
3. Resources for the Future, 1616 P St. NW, Washington, DC 20036, USA
4. Brookings Institution, 1775 Massachusetts Ave, NW Washington, DC 20036, USA