The risk of large volcanic eruption and the imapact of this risk on future ozone depletion

Abstract

Ozone depletion at mid-latitudes is caused by reactive halogens from man-made halocarboris. The stratospheric sulphate aerosol which follows large volcanic eruptions enhances (multiplies) this ozone depletion (it has no effect on ozone without halocarbons). Mid-latitude depletion almost doubled for the two years after Mt. Pinatubo. Although the Montreal Protocol is expected to reduce atmospheric amounts of halocarbons in the 21st century, stratospheric ozone will be at risk of depletion enhancement by large eruptions for the next 50 years. Mechanisms of volcanoes suggest that large eruptions are random and that their global rate is constant for several centuries. Measurements of large eruptions during the last 1000 years in ice cores have a remarkable fit to a Poisson distribution, reinforcing the conclusion that the global incidence is random and at a constant rate for this period. From this rate, the probability of one or more eruptions with at least the ozone-loss enhancement of Pinatubo is 58% in 50 years. This probability is large enough to be of serious concern for future mid-latitude ozone loss.