Climate change has obvious practical implications. It will kill millions of people, wipe out thousands of species, and so on. My question in this paper is much narrower. How might climate change impact on moral theory – and especially on the debate between utilitarians and their non-utilitarian rivals? I argue that climate change creates serious theoretical difficulties for non-utilitarian moral theories – especially those that based morality or justice on any contract or bargain for reciprocal advantage. Climate change thus tips the dialectical balance in favour of utilitarianism. However, I also argue that, because it upsets assumptions that lie behind the most plausible forms of modern utilitarianism, climate change may also push utilitarianism in a more austere and demanding direction.