HOLIVAR2006 Abstracts
Simulating the climate of the last two millennia: the role of internal and forced variability.
Hugues Goosse
Institut d'Astronomie et de Géophysique G. Lemaître, Université Catholique de Louvain, Belgium
Contact: Hugues Goosse (hgs@astr.ucl.ac.be)
For the pre-industrial period, the major forcings at interannual to centennial time scales are the solar and volcanic ones, with a contribution from the changes in land-use related to human activities, while orbital forcing plays a dominant role for lower frequency changes. On the other hand, for the last 150 years, anthropogenic forcings (i.e., mainly the increase in the greenhouse gas concentration and in the aerosol load) are the most important ones and it is impossible to simulate the observed warming during this period if those forcings are not included. At hemispheric scale, the surface temperature is strongly influenced by the variations of those external forcings. Nevertheless, at regional scale, the internal variability, which is purely due to the internal dynamics of the climate system, can mask the forced response. As a consequence, before the 20th century, cold or warm periods are rarely global, homogenous phenomena. Furthermore, the response to the forcing could be associated with changes in the frequency of some modes of variability. For instance, it has been proposed that, in response to a decrease in solar irradiance, the North Atlantic Oscillation tends to be in its negative phase. This induces cold conditions in Europe and thus a strong amplification of the response to the solar forcing in this region. This interplay between the response of the climate system to the various forcings and internal variability makes model-data comparison a complex task for the last millennia. Ensembles of simulation are very useful in this framework as they could provide a range of potential model behaviour.
Hugues Goosse graduated from the Université Catholique de Louvain, with a PhD in Mechanical Engineering. He is presently Research Associate at the Belgian National Fund for Scientific Research and Invited Professor at the Université Catholique de Louvain and the Ghent Universiteit. His research deals with two partly overlapping subjects: climate variability at high latitudes, with a focus on the sea-ice/ocean system, and the climate of the past millennia. His work is mainly devoted to modelling. His time is thus shared between on the one hand the analysis of model results and the model-data comparison and on the other hand the model development. In particular, he is involved in the development of an intermediate complexity model of the climate system, in collaboration with groups in Belgium, the Netherlands, and Germany. For more information, see http://www.astr.ucl.ac.be/users/hgs/