Empire has returned as a key political category in the last few years. It allows the politics of environment at the largest scale to be reconceptualized in interesting ways. Looking to imperial history and its ecological disruptions, to political ecology with its focus on the connections between rural production and metropolitan consumption, and in particular at the contemporary discussion of resource wars, this comment suggests that the focus on empire adds important dimensions to understanding global environmental politics. Not least empire requires a more explicit focus on the material contexts of contemporary politics and the violence that is connected to the extraction of resources, and petroleum in particular. Among other things this suggests a very different interpretation of the events of September 11 th 2001, and the importance of including much more than regimes and cooperation into the study of global environmental politics.