Global models of Earth’s climate have expanded beyond their geophysical heritage to include terrestrial ecosystems, biogeochemical cycles, vegetation dynamics, and anthropogenic uses of the biosphere. Ecological forcings and feedbacks are now recognized as important for climate change simulation, and the models are becoming models of the entire Earth system. This talk introduces Earth system models, how they are used to understand the connections between climate and ecology, and how they provide insight to environmental stewardship for a healthy and sustainable planet. Two prominent examples discussed in the talk are anthropogenic land use and land-cover change and the global carbon cycle. However, there is considerable uncertainty in how to represent ecological processes at the large spatial scale and long temporal scale of Earth system models. Further scientific advances are straining under the ever-growing burden of multidisciplinary breadth, countered by disciplinary chauvinism and the extensive conceptual gap between observationalists developing process knowledge at specific sites and global scale modelers. The theoretical basis for Earth system models, their development and verification, and experimentation with these models requires a new generation of scientists, adept at bridging the disparate fields of science and using a variety of research methodologies including theory, numerical modeling, observations, and data analysis. The science requires a firm grasp of models, their theoretical foundations, their strengths and weaknesses, and how to appropriately use them to test hypotheses of the atmosphere-biosphere system. It requires a reinvention of how we learn about and study nature.