Research Interests
Since my Ph.D., I have been fascinated by the interaction between land and atmosphere, ranging from processes in the turbulent surface-layer of the atmosphere to the energy budget and air flow over regions like the tidal areas of Northern Germany.
Stimulated by a presentation by Colin Prentice on modelling global vegetation zones, I looked at the global interaction between vegetation dynamics and atmosphere in a climate model. I found that the atmosphere – vegetation system can reveal multiple equilibria. For example in present-day climate, the Sahara could be a rather green savanna in its western parts.
A “green Sahara” existed several thousand years ago during the so-called Holocene climatic optimum. While the “greening of Sahara” was triggered by changes in the Earth orbit around the sun, it turns out that this astronomical forcing alone is not able to explain the magnitude of greening. A strong feedback between atmosphere and vegetation dynamics is a needed as an amplifier. With my former “CLIMBER working group” at the Potsdam Institute for Climate Impact Research I studied the climate system dynamics of past glacial (ice age) cycles, i.e., the dynamics of the coupled atmosphere – ocean – ice – biosphere – soils system, where I have been focussing on the question of whether or not vegetation dynamics amplifies climate changes between glacials and interglacials. Although number of modelling experiments seems to support this conjecture, this question is far from being solved.
Meanwhile, humans have modified the land surface by agriculture, forestry, tourism, and urbanisation. The CO2 emissions from deforestation have presumably almost cancelled the effects of changing the reflectivity, the roughness and the transpiration of used land surfaces. A number of studies indicate that this balance will not hold for future climate change. Therefore besides studying the dynamics of past climates, the interaction between humans – land – climate will be the focus of my work.