The interactive coupling of GCMs to predictive vegetation/ecosystem models, allowing realistic feedback between terrestrial ecosystems and the atmosphere, is an exciting advance in the Earth system approach to global climate modeling. Rob DeConto has been working with Dr. Dave Pollard (Penn State), Dr. Starley Thompson and Jon Bergengren (NCAR), in the application of interactive "climate-vegetation" models to past, present, and future climate scenarios. In one example, model simulations of the very warm, ice-free Cretaceous period (~100 Ma), illustrate the powerful controlling effect of terrestrial ecosystem distributions in the maintenance of continental equability during periods of extreme global warmth. In the ice-free Cretaceous, high-polar latitude forests dramatically reduced land-surface albedo, especially in the late winter and spring, by masking the high reflectance of snow cover. Surface to atmosphere latent heat flux, net radiation, and atmospheric moisture were increased, initiating annual warming feedbacks associated with high latitude sea surface temperatures via the seasonal thermal inertia of the ocean's mixed layer. Increased atmospheric moisture enhanced the water vapor feedback component of the greenhouse effect and increased the latent heat transport potential of the atmosphere. Sensitivity tests using coupled climate-vegetation models discovered internal climate-vegetation feedbacks (both physical and chemical), triggered by relatively small changes in forcing (e.g., atmospheric CO2, orbital parameters, ocean heat transport, etc.), that could have provided a strong amplifying feedback to climatic change throughout the Mesozoic and Cenozoic.