Comparison of the last interglacial climate simulated by a coupled global model of intermediate complexity and an AOGCM

The climate at the Last Interglacial Maximum (125 000 years before present) is investigated with the atmosphere-ocean general circulation model ECHAM- 1/LSG and with the climate system model of intermediate complexity CLIMBER- 2. Comparison of the results of the two models reveals broad agreement in m ost large-scale features, but also some discrepancies. The fast turnaround time of CLIMBER-2 permits one to perform a number of sensitivity experiment s to (1) investigate the possible reasons for those differences, in particu lar the impact of different freshwater fluxes to the ocean, (2) analyze the sensitivity of the results to changes in the definition of the modern refe rence run concerning CO2 levels (preindustrial versus "present"), and (3) e stimate the role of vegetation in the changed climate. Interactive vegetati on turns out to be capable of modifying the initial climate signals signifi cantly, leading especially to warmer winters in large parts of the Northern Hemisphere, as indicated by various paleodata. Differences due to changes in the atmospheric CO2 content and due to interactive vegetation are shown to be at least of the same order of magnitude as differences between the tw o completely different models, demonstrating the importance of careful expe rimental design.