Land cover influences on the regional climate of western North America during the early Eocene

We present results from an early Eocene (∼ 50–56 million years ago) regional modeling sensitivity experiment that examines the role of land cover, including the addition of vast areas of lakes or wetlands in regions where sedimentological and paleobotanical data indicate their past existence, in determining the regional climate of western North America. The spatial resolution of global climate models does not permit comparison of model results to proxy climate data in a way that helps to distinguish between regional and global climate forcings. Taking a regional modeling approach allows for higher resolution and reveals the contribution of a specific climate forcing mechanism to the climate of a region with relatively dense paleoclimate proxy data coverage. Our results suggest that adding lakes to the region brings the model results into closer agreement with proxy data estimates, and indeed, it seems critical to include these more realistic land cover types to capture the climate indicated by the proxy climate data. Within the grid cells that contain and surround the lakes, mean annual temperature increased as much as 3 °C and mean annual temperature range decreased as much as 9 °C. However, this important inclusion does not yield a regional climate that matches regional proxy data in all aspects, as mean annual precipitation gave mixed results. Therefore, other forcing factors, combined with land cover influences, must have played significant roles in defining the early Eocene climate.