1. A. Ando, Resources for the Future, 1616 P Street, NW, Washington, DC 20036, USA.
2. J. Camm, Department of Quantitative Analysis and Operations Management, University of Cincinnati, Cincinnati, OH 45221, USA.
3. S. Polasky, Department of Agricultural and Resource Economics, Oregon State University, Corvallis, OR 97331, USA.
4. A. Solow, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.