Such data are very extensive, and major efforts are underway to improve coverage in previously understudied regions, such as Siberia, central Asia, the high Arctic, and the wet tropics. This aim is to be achieved through a combination of modelling, data synthesis and data analysis. Key features of the 6000 yr BP climate include the more poleward extent of northern forests, and the greatly expanded African and Asian monsoon regions with vegetation and lakes in areas that are now arid. These features can be simulated by PMIP-type model experiements, but current models apparently underestimate their magnitude. Sensitivity experiments with appropriate changes to the land-surface conditions suggest that such changes may have provided the necessary amplification of the climate system's response to orbital forcing.
Further analysis requires coupling of climate and ecosystem process models.
Such efforts create a need for systematically constructed and properly documented global palacodata sets, above all for biome distribution at key times in the past, so that more rigorous palaeodata-model comparisons can be organized. This method has been tested using modern pollen assemblages in Europe, East Africa and West Africa. BP biome maps have now been created using the method for Europe and most of Africa, and are under construction for Australasia and eastern North America. The global data set will provide a comprehensive test of preliminary hypotheses already emerging from modelling studies and data-model comparisons. We propose to explore the implications of these preliminary results by running a more in-depth simulation with several models.