Research interests

My research focuses on climate system dynamics and climate history. I am particularly fascinated by the interaction between the atmosphere and the land surface with its vegetation. What role does this interaction play in the development of the global and regional climate and how does human activity affect the climate through land use?

In the early 1990s I coupled a model of vegetation zones with a climate model. Thereby, I learnt that the vegetation-climate system can assume different equilibrium states under the same climate forcing. This discovery led to the realization that an ecosystem can experience abrupt transitions as soon as external conditions change, not only through purely biological processes but also through its interaction with the climate. Changes in external conditions include, for example, the subtle, slow harmonic variations in the Earth's orbit around the sun, which alter the distribution of radiation on the Earth and the length of the seasons, or the current increase in greenhouse gases due to fossil fuel burning.

An important focus of my research is the climate history of the Sahara. I am interested in the following questions: Why was the Sahara much greener and wetter than today during warmer phases of the last several hundred thousand years? Why did the Sahara spread very rapidly, geologically speaking abruptly, in some areas and more gradually, in other areas a few thousand years ago ? Could the Sahara become greener again due to the current global climate change?