1. Department of Geography, Research Unit Spheres, The Hugo Observatory: Environment, Migration, Politics, University of Liège, Liège 4000, Belgium
2. Department of Sociology, University of Amsterdam, Amsterdam 1018 WV, the Netherlands
3. Centre for Sustainability Studies, Lund University, Lund 223 62, Sweden
4. Department of International Development, Community, and Environment, Clark University, Worcester, MA 01610-1477