The societal relevance of understanding complexities of earth system interactions is that human activity both affects these systems and is affected by changes in them. The goal of our research in this regard is to understand the complex and dynamic interactions between human and earth systems at the global scale, but resolved regionally. Our approach is to link a global model of the world economy, the Emissions Prediction and Policy Analysis (EPPA) model, with a comprehensive model of terrestrial hydrology and ecology and the physical climate system as controlled by atmosphere and ocean processes as they interact with terrestrial systems. At present, the physical and ecological system is resolved at a level that has come to be known as an earth system model of intermediate complexity, with less spatial resolution than a full-scale 3-dimensional Atmosphere-Ocean General Circulation Model (AOGCM) but with far more detail than the highly parameterized energy-balance-type models that have been widely used in integrated assessment. We sacrifice further resolution in the modeling of individual components of the earth system so that the Integrated Global System Model (IGSM) is computationally efficient, allowing us to evaluate very large ensemble runs (order 102-103). The desire to produce large ensemble simulations is driven by our interest in understanding the phenomenon of global environmental change as one of risk management. Research and modeling of the interaction of physical and ecological earth systems is described by Prinn (2006) and in greater detail in Sokolov et al. (2005).