Environmental consequences of natural resource exploitation often entail threats of future occurrences of detrimental abrupt events rather than (or in addition to) inflicting a damage gradually. The possibility of abrupt occurrence of climate-change related calamities is a case in mind. The uncertainty associated with the realization of these threats and their public-bad nature complicate the determination of optimal economic response. We analyze the regulation of such environmental threats by means of a Pigouvian hazard tax, based on the shadow cost of the hazard-generating activities. A numerical example illustrates possible effects of the proposed regulation scheme.