In recent years, several actors at the sub-national level (e.g. California, British Columbia, New York City) have taken unilateral steps to mitigate climate change by reducing their emissions. These developments have commanded considerable attention in the empirical literature. In this piece, we consider the philosophical dimensions of climate action at the sub-national level. Specifically, we argue that climate action at the sub-national level is an instance of a more general class of cases in which the failure of some collective agent to discharge some duty to which it is subject entails duties for the sub-collectives of which it is comprised to partially discharge that duty. We begin, then, with a discussion of such cases, and a defence of the devolution principle, which sets out conditions under which such duties arise. We then set out the argument with respect to sub-national political communities’ duties to take action on climate change, specifically. The article concludes by considering complications arising out of the inevitable fact of partial compliance, drawing upon recent work in the literature on slack-taking duties.