The Princeton University Ecosystem Dynamics (ED) model was used to develop a gridded dataset (at 1 degree resolution) of the United States landcover for 1700-1990. This dataset was validated against local observations. The Regional Atmospheric Modeling System (RAMS) was used to simulate the response of the climate system to the changing land cover/land use pattersn over the U. S. Preliminary investigations, comparing the climate of 1700 (pristine land cover), 1910 (maximum deforestation) and 1990 (current conditions), show that changing conditions at the land surface can have significant impacts on temperature and precipitation.