- Ingenieur Physicien, Free University of Brussels, 1971. (Engineer in Applied Physics).
- Ingenieur des Télécommunications et Electronique, Free University of Brussels, 1974. (Engineer in Telecommunications and Electronics).
- Docteur en Sciences Appliquées (Space Aeronomy), Free University of Brussels, 1976. (Ph.D.).
- Currently: Senior Scientist and Group Leader at the Max Planck Institute for Meteorology in Hamburg, Germany.
- Since 1 July 2011: Distinguished Scholar at the National Center for Atmospheric Research in Boulder, CO, USA
- From 1 July 2009 to May 31, 2014: Director of the Climate Service Center (CSC) in Hamburg, Germany (Helmholtz Zentreum Geesthacht), and External Member of the Max Planck Institute for Meteorology in Hamburg, Germany.
- From July 2009 to June 2011: Part-time Senior Scientist at the National Center for Atmospheric Research in Boulder, CO, USA
- From January 2006 to June 2009: Associate Director of the National Center for Atmospheric Research, and Head of the NCAR Earth and Sun Systems Laboratory (ESSL), Boulder, Colorado, USA.
- From October 1999 to January 2006 - Director at the Max-Planck-Institute for Meteorology, Hamburg (Department “Atmosphere in the Earth System”), and Member of the Max-Planck-Society, Munich, Germany
- From March 2000 to January 2006 - CEO and Scientific Director of the Deutsches Klimarechenzentrum (DKRZ) (German Climate Computing Center, Private Corporation hosting a supercomputing and data facility dedicated to climate modeling for the German scientific community), Hamburg, Germany
- From July 1990 to June 2011- Senior Scientist, National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA. Affiliated with the Atmospheric Chemistry Division (until 2001) and part-time as Senior Research Associate with the Advanced Study Program (2001-2005)
- April 1990 - December 1999: Director, Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA, and head of the Global Modeling Project.
- November 1995 - October 1996: Associate Research Director, Service d’Aéronomie du Centre National de la Recherche Scientifique (CNRS), Verrières-le-Buisson, France (Sabbatical from NCAR)
- August 1989 - April 1990: Acting Director, Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA
- June 1988 - July 1990: Scientist III, National Center for Atmospheric Research, Boulder, Colorado, USA. Head of the Atmospheric Chemistry Modeling Section
- September 1985 - June 1988: "Chercheur Qualifié" at the Belgian Fund for Scientific Research. (On leave as Visitor at NCAR, January-December 1986.)
- April 1985 - August 1985: Visiting Professor at the Max Planck Institute for Chemistry, Mainz, Germany (Director: P. Crutzen)
- September 1976 - March 1985: "Aspirant" at the Belgian Fund for Scientific Research. (On leave as a member from the Belgian House of Representatives, May 1977-December 1981.)
- September 1971 - August 1976: Research Assistant at the Belgian Institute for Space Aeronomy
