The first objective of this paper is to show that we cannot simply apply to risks associated with natural events insights and frameworks for moral evaluation developed in the literature by considering ordinary risks, technological risks and the risks posed by anthropogenic climate change. The second objective of this paper is to identify and develop a framework for the moral evaluation of the source of the risks associated with natural events, or the actions which sustain and impact such risks. Our discussion concentrates on the way the construction and modification of the built and natural environments can alter the probability of occurrence of natural events and the character and magnitude of the impact that such events have. We then argue for the need to develop a standard of reasonable care for decisions about the built and modified natural environment, which accounts for technical and resource constraints, as well as the place of natural hazard mitigation in public policy. The proposed standard will provide criteria for prioritizing risks to address and for identifying when mitigation action should be taken and which mitigation actions are most appropriate, including societal considerations.