Joint Seminar: Simulating the mid-Holocene ‘Green’ Sahara and its possible relationship to future states

The early to mid-Holocene in North Africa is a fascinating example of a fundamental natural environmental change. During this time much of the present-day Sahara was transformed by an expansion of vegetation and lakes. This conversion was caused by a substantial increase in precipitation that resulted from the change in insolation as a result of the variations in Earth’s orbit over thousands of years. However, simulations with a range of climate models have often failed to reproduce an adequate precipitation response for the mid-Holocene.

In this talk I’ll cover new simulations with the Hadley Centre GCMs aimed at understanding the ‘Green’ Sahara. I’ll begin with the potential role of mineral dust, which we quantify using three different dust model versions of the HadGEM2 Earth System model. After this I’ll switch focus to a set of ensembles with HadAM3 which we have used to optimise convection parameters, leading to a version of the Hadley Centre that can satisfy the mid-Holocene precipitation reconstructions over North Africa. This model still doesn’t ‘Green’, and I’ll discuss work to improve the vegetation moisture stress in the TRIFFID dynamic vegetation model. In the last part of the talk I’ll briefly discuss how a comparison of two simulation ensemble: the mid-Holocene one and a ‘future-like’ one, in which CO2 is doubled, may provide insight into the links between a skilful simulation of the ‘Green’ Sahara and future climate.




13:30 Uhr


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Peter Hopcroft, University of Birmingham


Martin Claussen

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