1. Graduate Student, Harvard Kennedy School, Harvard Univ., Cambridge, MA 02138.
2. Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Wisconsin–Madison, Madison, WI 53706 (corresponding author).
3. Research Scientist, Joint Program on the Science and Policy of Global Change, Massachusetts Institute of Technology, Cambridge, MA 02139-4307.
4. Professor, Civil and Environmental Engineering, Engineering Systems Division, Massachusetts Institute of Technology, Cambridge, MA 02139.