1. Center for Sustainability and the Global Environment, Nelson Institute for Environmental Studies, University of Wisconsin—Madison, 1710 University Avenue, Madison, Wisconsin 53726, United States
2. Joint Program on the Science and Policy of Global Change, Massachusetts Institute of Technology (MIT), 77 Massachusetts Avenue, MIT E19- 411, Cambridge, Massachusetts 02139-4307, United States
3. Department of Economics, University of Otago, PO Box 56, Dunedin 9054, New Zealand;
4. Department of Agronomy, University of Wisconsin—Madison, 1575 Linden Drive, Madison, Wisconsin 53706, United States