1. Department of Economic and Social Research, University of Cagliari, Viale S Ignazio 78, I-09123 Cagliari, Italy
2. Department of Land Engineering, University of Cagliari, Piazza D'Armi 16, I-09123 Cagliari, Italy
3. Department of Economic Policy, Finance and Development, Piazza S Francesco 7, I-53100 Siena, Italy, and Centre for Social and Economic Research on the Global Environment, University of East Anglia, Norwich NR4 7TJ, England