Climate of the Past www.clim-past.net 1814-9324 1814-9332 1 1 2005 10.5194/cp-1-1-2005 http://www.clim-past.net/1/1/2005/ http://www.clim-past.net/1/1/2005/cp-1-1-2005.html http://www.clim-past.net/1/1/2005/cp-1-1-2005.pdf 1 7 2005-10-04 Quantifying the effect of vegetation dynamics on the climate of the Last Glacial Maximum A. Jahn M. Claussen A. Ganopolski V. Brovkin Potsdam Institute for Climate Impact Research (PIK), P.O. Box 601203, 14412 Potsdam, Germany Now at Department of Atmospheric and Oceanic Sciences, McGill University, Burnside Hall Room 945, 805 Sherbrooke Street West, Montreal, Quebec, H3A 2K6, Canada Institute of Physics, Potsdam University, P.O. Box 601543, 14415 Potsdam, Germany The importance of the biogeophysical atmosphere-vegetation feedback in comparison with the radiative effect of lower atmospheric CO₂ concentrations and the presence of ice sheets at the last glacial maximum (LGM) is investigated with the climate system model CLIMBER-2. Equilibrium experiments reveal that most of the global cooling at the LGM (-5.1°C) relative to (natural) present-day conditions is caused by the introduction of ice sheets into the model (-3.0°C), followed by the effect of lower atmospheric CO₂ levels at the LGM (-1.5°C), while a synergy between these two factors appears to be very small on global average. The biogeophysical effects of changes in vegetation cover are found to cool the global LGM climate by 0.6°C. The latter are most pronounced in the northern high latitudes, where the taiga-tundra feedback causes annually averaged temperature changes of up to -2.0°C, while the radiative effect of lower atmospheric CO₂ in this region only produces a cooling of 1.5°C. Hence, in this region, the temperature changes caused by vegetation dynamics at the LGM exceed the cooling due to lower atmospheric CO₂ concentrations.