Assessing and Simulating the Altered Functioning of the Earth System in the Anthropocene

The current human-dominated era or "Anthropocene" has been a time of unprecedented rates of change within the Earth system. As such the Anthropocene poses a no-analogue situation in which evidence of past Earth system changes cannot, on their own, tell us of how the system will respond in the future. Instead, we need to develop mechanistic and phenomenological models based on robust underlying principles to extrapolate our knowledge of the past Earth system into projections of the future . This requires an entire spectrum of Earth system models that can be related to each other in a more rigorous vvay than has been achieved to date. It also requires new integrated models of the two-way coupling between the biophysical and human aspects of the Earth system. Only then will we be able to approach all of the paleodata constraints on Earth system dynamics (which requires long simulations), while also providing regionally specific Earth system projections and spatially specific human development paths for policy makers (which requires, in both cases, high-resolution comprehensive models as well as models that can bridge spatial and temporal scales) . Such a spectmm of models offers a solution to the tension between "simulation," which inevitably leads to increasing model complexity, and "understanding," which often involves reducing the system to its bare necessities.