Anthropogenic climate change, with co-factors, threatens civilization, and thus human health. I first show that climate change is an important element of a system of hazards called “Limits to Growth”. I then argue that the interaction of climate change and other Limits to Growth elements risks civilization “failure” and possibly its “collapse”. Either consequence, were one to occur, entails profound risks to global population health, yet appreciation of this is still largely outside the health literature. I then discuss these relationships (including with civilization's destiny) with bioethical schools. The oldest of these (also called medical ethics) is strongly related to health and medicine, but in a later (1970) formulation the prefix “bio” is broader than human biology, though this school also has roots in human health. Van Rensselaer Potter, widely recognized as the founder of this school, subtitled it “the science of survival”. This subtitle seems to acknowledge an at least implicit risk to civilization. I also briefly discuss environmental ethics. By calling for greater discussion of the risk of civilization failure (or its collapse) this paper makes an important and original contribution to bioethics, however conceptualized. The major scholarly contribution of this paper is its call for the human health literature to refresh its consideration of Limits to Growth, to reconsider aspects that have become marginalized in the health literature, and for health workers to deepen their engagement with related literatures, especially of human ecology. We must contemplate the unthinkable if we are to help avert it.