Tropical paleoclimates at the Last Glacial Maximum: comparison of Paleoclimate Modeling Intercomparison Project (PMIP) simulations and paleodata

Seventeen simulations of the Last Glacial Maximum (LGM) climate have been p erformed using atmospheric general circulation models (AGCM) in the framewo rk of the Paleoclimate Modeling Intercomparison Project (PMIP). These simul ations use the boundary conditions for CO2, insolation and ice-sheets, surf ace temperatures (SSTs) are either (a) prescribed using CLIMAP data set (ei ght models) or (b) computed by coupling the AGCM with a slab ocean (nine mo dels). The present-day (PD) tropical climate is correctly depicted by all t he models, except the coarser resolution models, and the simulated geograph ical distribution of annual mean temperature is in good agreement with clim atology. Tropical cooling at the LGM is less than at middle and high latitu des, but greatly exceeds the PD temperature variability. The LGM simulation s with prescribed SSTs underestimate the observed temperature changes excep t over equatorial Africa where the models produce a temperature decrease co nsistent with the data. Our results confirm previous analyses showing that CLIMAP (1981) SSTs only produce a weak terrestrial cooling. When SSTs are c omputed, the models depict a cooling over the Pacific and Indian oceans in contrast with CLIMAP and most models produce cooler temperatures over land. Moreover four of the nine simulations, produce a cooling in good agreement with terrestrial data. Two of these model results over ocean are consisten t with new SST reconstructions whereas two models simulate a homogeneous co oling. Finally, the LGM aridity inferred for most of the tropics from the d ata, is globally reproduced by the models with a strong underestimation for models using computed SSTs.