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 conditions have on global climate. Global mean climate changes little in response to the subtle changes we made; differences in mean annual and seasonal surface temperatures over northern and southern hemispheric land, respectively, are on the order of 0.5 degreesC. In contrast, and perhaps more importantly, continental scale climate exhibits significant responses. Increased peak elevations and topographic detail result in larger amplitude planetary similar 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 elevation modifications. Increased leaf area index (LAI), as a result of altered vegetation distributions, reduces temperatures by up to 6 degreesC. Decreasing the size of the Mississippi embayment decreases inland precipitation by 1-2 mm/day. These climate responses to increased accuracy in boundary conditions indicate that improved boundary conditions may play an important role in producing modeled paleoclimates that approach the proxy data more closely. (C) 2000 Elsevier Science B.V. All rights reserved.