Individual responsibility for carbon emissions: Is there anything wrong with overdetermining harm?

Climate change and other harmful large-scale processes challenge our understandings of individual responsibility. People throughout the world suffer harms—severe shortfalls in health, civic status, or standard of living relative to the vital needs of human beings—as a result of physical processes to which many people appear to contribute. Climate change, polluted air and water, and the erosion of grasslands, for example, occur because a great many people emit carbon and pollutants, build excessively, enable their flocks to overgraze, or otherwise stress the environment. If a much smaller number of people engaged in these types of conduct, the harms in question would not occur, or would be substantially lessened. However, the conduct of any particular person (and, in the case of climate change, of even quite large numbers of people) could make no apparent difference to their occurrence. My carbon emissions (and quite possibly the carbon emissions of much larger groups of people dispersed throughout the world) may not make a difference to what happens to anyone. When the conduct of some agent does not make any apparent difference to the occurrence of harm, but this conduct is of a type that brings about harm because many people engage in it, we can call this agent an overdeterminer of that harm, and their conduct overdetermining conduct. In this essay we explore the moral status of overdetermining harm.