[1] EASAC, D-06019 Halle An Der Saale, Germany
[2] German Natl Acad Sci, D-06019 Halle An Der Saale, Germany
[3] EASAC Working Grp CCS, Cambridge CB3 0WA, England
[4] Univ Cambridge, Inst Theoret Phys, Cambridge CB3 0WA, England
[5] EASAC Energy Programme, Oxford OX1 3AN, England
[6] Univ Oxford, Dept Earth Sci, Oxford OX1 3AN, England