Many major questions in earth science research today are not matters of the behavior of physical systems alone, but of the interaction of physical and social systems. Information and assumptions about human behavior, human institutions and infrastructures, and human reactions and responses, as well as consideration of social and monetary costs, play a role in climate prediction, hydrological research, and earthquake risk assessment. The incorporation of social factors into "physical" models by scientists with little or no training in the humanities or social sciences creates ground for concern as to how well such factors are represented, and thus how reliable the resulting knowledge claims might be. Yet science studies scholars have scarcely noticed this shift, let alone analyzed it, despite its potentially profound epistemic – and potentially social – consequences.