THE GREENING OF THE SAHARA DURING THE MIDHOLOCENE - RESULTS OF AN INTERACTIVE ATMOSPHERE-BIOME MODEL

An asynchronously coupled atmosphere biome model was used to assess th e biogeophysical interaction during the mid-Holocene, 6000 years befor e present. The model determines its own land surface conditions and ca n, therefore, predict quasiequilibrium changes in global vegetation pa tterns. For the mid-Holocene, the coupled model simulated a northward shift of savanna up to 20 degrees N into the Sahara which in turn ampl ified the response of the atmospheric circulation to changes in the Ea rth's orbit during the Holocene. Moreover, in the simulation, most of the western part of the Sahara appeared to be vegetated by xerophytic woods/shrub and warm grass, while the eastern part remained a desert. The simulated vegetation distribution agreed better with palaeobotanic al reconstructions than results from the same model, but omitting vege tation-atmosphere interaction.