Climate sensitivity to changes in land surface characteristics

Using a recently developed global vegetation distribution, topography, and shorelines for the Early Eocene in conjunction with the Genesis version 2.0 climate model, we investigate the influences that these new boundary condi tions have on global climate. Global mean climate changes little in respons e to the subtle changes we made; differences in mean annual and seasonal su rface temperatures over northern and southern hemispheric land, respectivel y, are on the order of 0.5 degreesC. In contrast, and perhaps more importan tly, continental scale climate exhibits significant responses. Increased pe ak elevations and topographic detail result in larger amplitude planetary s imilar to4 mm/day and decreases by 7-9 mm/day in the proto Himalayan region . Surface temperatures change by up to 18 degreesC as a direct result of el evation modifications. Increased leaf area index (LAI), as a result of alte red vegetation distributions, reduces temperatures by up to 6 degreesC. Dec reasing the size of the Mississippi embayment decreases inland precipitatio n by 1-2 mm/day. These climate responses to increased accuracy in boundary conditions indicate that "improved" boundary conditions may play an importa nt role in producing modeled paleoclimates that approach the proxy data mor e closely. (C) 2000 Elsevier Science B.V. All rights reserved.