In this paper, I argue that Stoic thought can make a significant and valuable contribution to modern environment ethics, particularly in providing an ethical and conceptual framework for responding effectively to climate breakdown. The contribution centres on three points. (1) Key distinctive features of Stoic ethical thought (including their thinking on the unity of virtue, the virtue-indifferents distinction, and the community of humankind) can be deployed to support the claim that, in our current emergency, environmental action should have moral priority over other claims. (2) Salient links between Stoic ethics and the Stoic worldview reinforce the idea that, in our present situation, both virtue and happiness need to be understood in a way that involves ‘living according to nature’, in the sense of giving priority to environmental action. (3) Stoic thinking about the worldview, including their ideas about order and disorder in nature, and about the goodness of the world, can serve to support an ‘ecocentric’ viewpoint and validate action to tackle climate breakdown. As is obvious from this summary, my paper aims at selective adoption of Stoic ideas for modern purposes and not at historical interpretation of Stoic thought for its own sake. However, my discussion rests on what I take to be defensible readings of the ancient Stoic sources and on credible interpretation of them.