Plenary Speaker - Martin Claussen
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Biography
Martin Claussen is Professor of Meteorology at the Meteorological Institute, University Hamburg, and Director at the Max Planck Institute for Meteorology, Hamburg (Germany). His scientific expertise is meteorology, climate modeling, palaeo-climate modeling, and land surface – atmosphere interaction. He is interested in analyzing feedback processes in the climate system in present and past climate. He was one of the first to couple a dynamics vegetation model to an atmospheric circulation model to explore the role of vegetation – atmosphere interaction in the climate system.
Claussen is member of the IGBP-SC. He has served as chair and vice chair of the German Meteorological Society, and as member of the Senate of the German Research Foundation. Claussen has received the Milutin Milankovic Medal, European Geosciences Union (2005), and he is member of several academies including the German (National) Academy of Sciences, Leopoldina, and the Academia Europaea. For more information, visit Dr. Claussen's web page.
Abstract: Abrupt or not abrupt? - Tipping points in biogeophysics
Large-scale changes in climate and vegetation that appear to be abrupt in comparison with external forcing frequently occurred in the past. Such changes are interesting from the dynamical systems point of view because they could come as a surprise: Even if the change in the forcing is known, the onset of the resulting climate and vegetation change cannot precisely be predicted. Furthermore, abrupt changes are of high socio-economic relevance, if they occur ‘so rapidly and unexpectedly that human and natural systems have difficulties adapting to it’. An illustrative example from the Holocene is the abrupt onset and, at least regionally, abrupt termination of the African Humid Period which is associated with large changes in the Saharan ecosystems and human cultures. From climate simulations and geological data the picture of an abrupt termination of the African Humid Period and abrupt expansion of the Sahara around 5,500 years ago emerged, and the Sahara was viewed as one of the “tipping elements” of the Earth system. More recent data and climate modeling lead to a critical reassessment. Here, a more comprehensive view is proposed. It is shown that abrupt change can result from a strong biogeophysical feedback or, alternatively, from intrinsic threshold behaviour of hydrological systems and ecosystems. Strong feedback in one region can lead to ‘induced tipping’ in other, seemingly stable regions. Finally, biodiversity affects the strength of biogeophysical feedback. In conclusion, the nature of abrupt change cannot be determined from statistical analysis of palaeo time series without knowledge of the underlying biogeophysical processes.
