How should we evaluate public policies or projects to avert or reduce the likelihood of a catastrophic event? Examples might include a greenhouse gas abatement policy to avert a climate change catastrophe, investments in vaccine technologies that would help respond to a \mega-virus,” or the construction of levees to avert major flooding. A policy to avert a particular catastrophe considered in isolation might be evaluated in a cost-benefit framework. But because society faces multiple potential catastrophes, simple cost-benefit analysis breaks down: Even if the benet of averting each one exceeds the cost, we should not necessarily avert all of them. We explore the policy interdependence of catastrophic events, and show that considering these events in isolation can lead to policies that are far from optimal. We develop a rule for determining which events should be averted and which should not.

JEL Classication Numbers: Q5, Q54, D81

Keywords: Catastrophes, catastrophic events, willingness to pay, policy objectives, climate change, pandemics, nuclear terrorism.