CLIMCYC: Modeling of the Last Glacial Cycle: Response of Climate and Vegetation to Insolation Forcing Between 132-112 ka BP

The last ice age is known for high frequency climate fl uctuations that cannot be explained by astronomical forcing alone. Therefore, an accurate simulation of internal feedbacks between individual climate subsystems is absolutely necessary. In the set of experiments presented here, the model’s ability to simulate climate feedbacks from the land biosphere has been verifi ed by transient simulations with both the ECHAML/LSG and the ECHAM/LSG/LPJ model. The experiments were performed with a time-varying insolation from 132 ka proceeding to 112 ka. This time frame covers the transition from the last interglacial to the following glacial and is therefore ideal for the study of climate feedbacks. Figure 1 shows the response of near surface summer temperature to the astronomical forcing in the northern hemisphere. The stronger cooling of the northern hemisphere in the model version with included vegetation model LPJ is mainly due to the replacement of forest with lighter grass or even snow areas in the higher latitudes. This effect is important for the establishment of continental ice sheets and the inception of glacials. since it increases the albedo, thus amplifying the astronomical forcing. In both model versions, intensifi ed insolation during the interglacial stage 5e leads to higher precipitation over most of the continents. The maximum response is registered in the tropics and the African-Asian monsoon belt (Fig. 2), due to higher land-sea temperature contrasts. Vegetation is established in the western part of the Sahara desert. This reduces the local albedo, which further amplifi es the land-sea temperature contrast, thereby strengthening the summer monsoon. The resulting change in monsoonal precipitation exceeds the response simulated by the model with non-dynamic vegetation by more than two-fold in this area. Changes simulated by the dynamical vegetation model are most pronounced in the boreal regions of northern Asia, North America, in the tropics, and in the African-Asian monsoon belt. In the latter regions, an increased (decreased) vegetation