The Arctic will be affected by global warming much more than any other region of the world bearing global consequences by albedo decrease, freshwater runoff, carbon release, and changes in biodiversity (ACIA, 2004). Looking for analogues of climate warming and biotic response, we previously reconstructed vegetation and climate in the most continental and climatically most stable part of the terrestrial Eurasian Arctic during warm extremes of the Eemian and Early Holocene interglacials and during the Mid Weichselian interstadial in contrast to the Late Holocene (Kienast et al. 2005, Kienast et al. submitted). Our reconstructions base on plant macrofossils preserved in East Siberian permafrost deposits.Accordingly, all warm phases except for the Late Holocene show similar vegetation patterns supporting a mosaic of several plant communities including boreal aquatics, floodplain meadows with halophytes and steppes at times supplemented by shrubs and wetlands. During the Late Holocene in contrast, the fossil species spectra indicate a dramatic decrease in diversity of vegetation types and available habitats (Kienast 2006). From about 5000 years BP on, the species spectra consist almost exclusively of wetland plants reflecting permanently wet conditions and low summer temperature. This event coincides with a global temperature decrease and with the establishment of the modern coast line in the Laptev Shelf region (Bauch et al. 2001) resulting in humidification of Arctic East Siberia.The described differences and, in particular, the analogy of climate and vegetation during the Eemian and the pre-transgression stage of the Early Holocene indicate that the Northeast Siberian shelves have been during former warm stages, including the Eemian, much less inundated than now resulting in higher continental climate. Accordingly, the oceanic influence on climate due to the vast Holocene marine transgression in North Siberia is a very young phenomenon and probably the result of tectonic extension and subsidence of the Laptev and the western East Siberian Shelves.To highlight differences between both warm stages and to reveal consequences of the assumed coast line shift, we proposed a new project at the German Research Foundation (DFG). As a part of that project, we intend to reconstruct the Eemian and Holocene thermal optima in the Northeast Siberian shelf region more in detail, both quantitatively and qualitatively. Simultaneous to these reconstructions, a coupled ocean-atmosphere general circulation model (ECHO-G) will be used within that project to explain responsible mechanisms, global and regional, resulting in climatic differences. Climate patterns, formerly simulated with that model, were, e.g. in Europe, in good agreement with reconstructions (Kaspar et al., 2005). In adjusting the models set-up, it is to be clarified whether the climatic differences between both warm stages can be explained by global insolation changes alone or if internal climate parameters such as the supposed alteration of the land-sea mask in the study region amplified the external insolation effect.