HOLIVAR2006 Abstracts
Rapid land cover changes - theory and potential implications.
Martin Claussen
Potsdam Institute for Climate Impact Research, Potsdam, D - 14412, Germany
Contact: Martin Claussen (claussen@pik-potsdam.de)
It is now commonly accepted that climate has changed rapidly in the past and will do so in the future. Examples are the meridional overturning circulation in the Atlantic which could explain the rapid climate swings during the last glacial, or the snow-albedo feedback which might have led to a rapid onset of glacials. Also ecosystems such as lakes, coral reefs, or forests are known to exhibit regime shifts.
Meanwhile it has been realised that large-scale vegetation dynamics can affect the hydrological cycle in a strongly non-linear way thereby leading to – in comparison with climate forcing – abrupt climate changes. The expansion of Sahara some 5500 years ago from a rather green state to its present-day extent is an illustrative example. The underlying biogeophysical feedback mainly involves the interaction between the high albedo of deserts and the subtropical atmospheric circulation. The decadal variability in Sahelian rainfall during the last century has been interpreted in terms of a strong biogeophysical feedback being triggered by changes in Atlantic sea-surface temperatures. It has been postulated that the Namibian desert, the eastern Amazon forests, and the caatinga (dry open forest) in North-east Brazil are also prone to abrupt changes. Shifts in the boreal tree line, on the other hand, have been found to behave more gradually without bifurcation of the system.
Rapid land-cover changes likely impact on human society. Presumably, the expansion of the Sahara has affected, or even initiated, the advance of high civilisations along the Nile. Hence future research will have to address questions of whether rapid large-scale vegetation / precipitation changes will occur in Northern Africa and whether similar non-linear biogeophysical feedbacks could be triggered directly of indirectly by humans in other regions on Earth.
Martin Claussen graduated from the University of Hamburg in 1984 where he received his diploma in Meteorology and his Dr.rer.nat. (Ph.D.). After working some years at the Research Center in Geestacht on atmosphere – land surface interaction at local and global scales, he became head of the climate system department at the Potsdam Institute for Climate Impact Research (PIK) in 1996 and managing director of PIK in 2002. At the same time he was Professor for Theoretical Climatology at the Free University, Berlin, and from 2002 to 2005, Professor for Climate Physics at Potsdam University. Since 2005, he has been Professor for Meteorology at the University Hamburg and Director at the Max Planck Institute for Meteorology, Hamburg. He has worked on several national and international committees, and for the last 3 years, he has been chair of the German Meteorological Society. He is mainly interested in feedback processes in the climate system in present and past climate with emphasis on atmosphere – land interaction.