<www.sciamdigital.com/index.cfm?fa=Products.ViewIssuePreview&ARTICLEID_CHAR=590CD42C-5C8B-411D-ABA9-70D3339E6FD> Also available as IIASA Interim Report IR-02-020 <www.iiasa.ac.at/Admin/PUB/Documents/IR-02-020.pdf>