ORIGINAL PAPER Impacts of tectonic and orbital forcing on East African climate: a comparison based on global climate model simulations Frank Kaspar • Kerstin Pro ¨mmel • Ulrich Cubasch Received: 16 December 2008 / Accepted: 23 February 2010 / Published online: 7 April 2010 Ó Springer-Verlag 2010 Abstract A global atmosphere–ocean model has been forced with topographic and orbital scenarios in order to evaluate the relative role of both factors for the past climate of East Africa. Forcing the model with a significantly reduced topography in Eastern and Southern Africa leads to a distinct increase in moisture transport from the Indian Ocean into the eastern part of the continent and increased precipitation in Eastern Africa. Simulations with step-wise reduced height show that this climate change occurs con- tinuously with the change in topography, i.e., an abrupt change of local climatic features with a critical height is not found. Simulations of the last interglacial (at 125,000 years before present, i.e., the Eemian interglacial) and the last glacial inception (at 115,000 years before present) are used as examples for the role of orbital- induced changes in insolation. Here, changes in meridional temperature gradients lead to modifications in moisture transport of similar order of magnitude, but with different spatial and seasonal structure. For the Eemian interglacial, a distinct increase in summer moisture transport from the Atlantic deep into the continent at around 20°N is simulated. Keywords Climate simulation Á Paleoclimate Á Africa Á East African Rift System Á Tectonics Á Orbital forcing Á Interglacial Á Glacial Á Quaternary Á Cenozoic Á Human evolution Introduction A number of paleoclimatic records suggest a relationship between climate-driven environmental changes in East Africa and human evolution (for an excellent review, see Maslin and Christensen 2007, and references therein). The analysis of past climate changes in that region is therefore an important contribution for the understanding of human evolution. During the last 10 million years, East African climate was controlled by local tectonics, orbital forcing and global climate changes (Maslin and Christensen 2007). Variations in the Earth’s orbit around the Sun induce changes in the seasonal cycle of insolation, which are considered to be responsible for the cycles of glacials and interglacials during the last 500,000 years. Ice core data indicate that intergla- cials occurred with a frequency of around 100,000 years during the last 500,000 years. These interglacials are also visible in sediments from low latitudes (e.g., Tjallingii et al. 2008). Three parameters are responsible for the seasonal distribution of insolation: the eccentricity of the Earth’s orbit, the angle of the axis of rotation (obliquity) and the position of the equinoxes relative to the perihelion (pre- cession). The direct effects of insolation in the tropics are mainly due to eccentricity-modulated precession, but trop- ical climate may also be influenced by high-latitudinal climate change. The Eemian was the last interglacial before the present one and lasted approx. from 130,000 years before present F. Kaspar (&) Á K. Pro ¨mmel Á U. Cubasch Institute for Meteorology, Freie Universita ¨t Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany e-mail: frank.kaspar@dwd.de Present Address: F. Kaspar Satellite Application Facility on Climate Monitoring (CM-SAF), Deutscher Wetterdienst, Offenbach, Germany 123 Int J Earth Sci (Geol Rundsch) (2010) 99:1677–1686 DOI 10.1007/s00531-010-0538-x