Plants serve as a key link in the global carbon and hydrologic cycles, regulating earth’s temperature, humidity, and atmospheric composition. In the presence of elevated CO2 concentrations, plants are expected to respond through increased photosynthesis and reduced stomatal conductance. However, the impacts of these vegetation changes on regional and global climate are largely unknown. In this talk, I’ll use a suite of earth system model experiments to understand and estimate the contribution of CO2-induced vegetation changes to projections of future anthropogenic climate change. I’ll show that a reduction in stomatal conductance is the primary means by which elevated CO2 impacts vegetation’s role as a climate change agent. As stomatal conductance goes down, vegetation pumps less subsurface water to the boundary layer, altering energy and moisture fluxes throughout forested regions of the tropics and mid to high latitudes. These flux changes have a substantial impact on the spatial pattern and intensity of rainfall, as well as the frequency and duration of extreme temperature events. Though there remains considerable uncertainty in the representation of vegetation physiology in climate models, the results suggest that the response of vegetation to elevated CO2 may be as important as the radiative impact of CO2 in shaping climate change in some forested regions.