Hans Joachim Schellnhuber is Research Director of the Tyndall Centre, School of Environmental Sciences, University of East Anglia and Founding Director of the Potsdam Institute for Climate Impact Research, Germany.

Paul J. Crutzen is Professor Emeritus in the Division of Atmospheric Chemistry at the Max Planck Institute for Chemistry in Mainz, Germany, and Professor at Scripps Institution of Oceanography; he was corecipient of the Nobel Prize for Chemistry in 1995.

William C. Clark is Harvey Brooks Professor of International Science, Public Policy, and Human Development at the Kennedy School of Government at Harvard University.

Martin Claussen is Managing Director and Head of the Climate System Department at the Potsdam Institute for Climate Impact Research.

Hermann Held is Head of the Mitigation Options research group within the Department of Integrated Systems Analysis at the Potsdam Institute for Climate Impact Research.