A conceptual model is presented of the Earth System appropriate to global change on timescales of decades to centuries. This is used as a framework for discussion of the processes and feedbacks involved in the physical climate system and in biogeochemical cycles, and the expected role of remote sensing in understanding them. Demonstrated and potential opportunities for space-related observations are identified in the context of broader needs for information about the various subsystems, concluding with a brief discussion of the program needed to better understand the impact of human activities on the global environment in the context of natural variability.