Professor of Energy Economics at the Vienna University of Technology. Acting Deputy Director of the International Institute for Applied Systems Analysis (IIASA) and Director of the Global Energy Assessment; Coordinating Lead Author of the Intergovernmental Panel of Climate Change (IPCC), Fourth Assessment Report; Coordinating Lead Author of the Millennium Ecosystem Assessment. Convening Lead Author of the Second Assessment Report of the IPCC (1993-95), Convening Lead Author of the IPCC Special Report on Emissions Scenarios (1997 to 2000); Lead Author of Third Assessment Report of the IPCC (1999 - 2001); Convening Lead Author of the World Energy Assessment (1999 to 2000); Guest Professor at Graz University of Technology (1993-2003). Since 2008 member of the WBGU.
