MODELING OF MIDDLE PLIOCENE CLIMATE WITH THE NCAR GENESIS GENERAL-CIRCULATION MODEL

A climate modeling study was carried out which used boundary condition s created by the USGS PRISM group. The model used for this study is th e National Center for Atmospheric Research (NCAR) GENESIS climate mode l. GENESIS is an atmospheric general circulation model (GCM) that is c oupled to. a land-surface model and contains submodels for snow and so il. Boundary conditions incorporated into the model which were specifi c to the middle Pliocene (similar to 3 Ma) are (1) present day contine nt configuration, modified by a 35 m rise in sea level, (2) modified p resent day elevations, (3) reduced continental ice cover on both Green land and Antarctica, (4) Pliocene vegetation, and (5) Pliocene sea sur face temperatures (SSTs) and sea ice distribution. Atmospheric pCO(2) and orbital parameters were set at current values: The greatest influe nce of the specified warm SSTs upon the resulting climate was occurren ce of warmer and more humid high latitudes than observed in the curren t climate, especially in the winter season. The global mean surface te mperature was 3.6 degrees C warmer than in a present day control case, and global mean precipitation increased by 5% relative to the control case, with most excess precipitation occurring over the African conti nent and the oceans. Zonal winds weakened slightly in the Pliocene cas e but Hadley cell extent and jet stream locations were unchanged relat ive to the control case. Model results predict specific areas in which middle pliocene climate should have differed substantially from the p resent climate, which can be tested with paleoclimate data.