THE CLIMATE OF EUROPE 6000 YEARS AGO

Palaeoclimates across Europe for 6000 y BP were estimated from pollen data using the modern pollen analogue technique constrained with lake- level data. The constraint consists of restricting the set of modern p ollen samples considered as analogues of the fossil samples to those l ocations where the implied change in annual precipitation minus evapot ranspiration (P-E) is consistent with the regional change in moisture balance as indicated by lakes. An artificial neural network was used f or the spatial interpolation of lake-level changes to the pollen sites , and for mapping palaeoclimate anomalies. The climate variables recon structed were mean temperature of the coldest month (T-c), growing deg ree days above 5 degrees C (GDD), moisture availability expressed as t he ratio of actual to equilibrium evapotranspiration (alpha), and P-E. The constraint improved the spatial coherency of the reconstructed pa laeoclimate anomalies, especially for P-E. The reconstructions indicat e clear spatial and seasonal patterns of Holocene climate change, whic h can provide a quantitative benchmark for the evaluation of palaeocli mate model simulations. Winter temperatures (T-c) were 1-3 K greater t han present in the far N and NE of Europe, but 2-4 K less than present in the Mediterranean region. Summer warmth (GDD) was greater than pre sent in NW Europe (by 400-800 K day at the highest elevations) and in the Alps, but >400 K day less than present at lower elevations in S Eu rope. P-E was 50-250 mm less than present in NW Europe and the Alps, b ut alpha was 10-15% greater than present in S Europe and P-E was 50-20 0 mm greater than present in S and E Europe.