IMPACT OF REDUCED TROPICAL SEA SURFACE TEMPERATURES ON THE RECONSTRUCTION OF CLIMATE AND LAND VEGETATION AT THE LAST GLACIAL MAXIMUM

Many atmospheric general circulation model (AGCM) simulations of last glacial maximum (LGM) climate have been based on the CLIMAP reconstructions of sea surface temperatures (SSTs). Recently, CLIMAP SSTs for the LGM have been shown to be too warm in the tropical region. Model vegetation reconstructions which are based on the results of such climate simulations can thus be expected to yield significant errors leading for instance to an overestimate of the area of tropical forests at the LGM. A sensitivity test is performed with the CARAIB dynamic global vegetation model to study the impact of colder tropical SSTs on the reconstructed LGM vegetation. Climatic outputs from the ECHAM AGCM are used to force the CARAIB model. Two LGM ECHAM simulations are compared: (1) run with 21 ky BP insolation, 200 ppmv of CO₂, SSTs and glaciers from CLIMAP, (2) run with same conditions as in (1), but with SSTs reduced by 3 °C in the tropical region. The climatic anomalies of both simulations are combined with a reference present-day observed climatology to produce two sets of LGM climatic fields which are then used by CARAIB to reconstruct the vegetation distribution and the land carbon storage. The results of both simulations are compared with proxy vegetation data.