Understanding the probability distribution of the outcomes and costs of a policy to restrict POD emissions requires assessment and convolution of uncertainties about a wide range of factors. These include the future emission trajectories of potential ozone depleters and of other gases that influence ozone concentrations, the effect of a specified set of emission paths on actual ozone concentrations, the increase in UV flux to the earth’s surface and its effects on human health, crop yields, other aspects of the biosphere, degradation of materials, and other consequences of policy interest. Uncertainties about each of these factors contribute to uncertainty about the magnitude of the potential threat and the effects of alternative global strategies for controlling POD emissions. Moreover, the presence of this pervasive uncertainty is an important factor in choosing an appropriate policy, since a more flexible policy may be preferred to alternatives that would perform better in a more certain environment.