In this Article, I suggest two different but related ways of reframing the public discourse on climate change. First, I propose that we move further in the direction of characterizing climate change as a public health threat and not only as an environmental threat. Second, I argue that we should stop thinking of responses to climate change in terms of the precautionary principle, which counsels action even in the absence of scientific consensus about a threat. We should speak instead in terms of a ?post-cautionary? principle for a post-cautionary world, in which some very bad effects of climate change are unavoidable and others are avoidable only if we take dramatic steps, and soon. These points are related insofar as they together create a moral imperative both to adapt to the changes we cannot prevent and to mitigate those we can. Without these efforts, people will fall ill and many will die, and we know now that this will occur. No fancy moral theory is required to condemn, and to make every attempt to avert, this large-scale knowing killing.