1. Walker Institute for Climate System Research, Department of Agriculture, University of Reading, Reading RG6 6AR, UK.
2. Department for International Development, 22-26 Whitehall, London SW1A 2EG, UK.
3. ZEF B: Center for Development Research, Department of Economic and Technical Change, University of Bonn, Walter-Flex-Strasse 3 53113 Bonn, Germany.