FOR most of the world, the threat of increased solar ultraviolet (UV) exposure as the ozone layer thins is still theoretical. But that threat has materialized on the fringes of the Antarctic ozone hole. Ozone-depleted air drifting north as the ozone hole breaks up can pass over southern Australia and New Zealand. Colin R. Roy, H. Peter Gies, and Graeme Elliott of the Australian Radiation Laboratory at Yallambie, Victoria, used data from a December 1987 event to investigate increased UV exposure.
They found that ultraviolet irradiance did indeed go up as ozone-poor air moved in. Cloud cover kept the UV radiation within normal limits that December. But the scientists also found that at their low southern latitude the percentage increase in effective ultraviolet B irradiance for a 1 percent decrease in ozone was about a factor of 2.
In a letter to Nature magazine last September, they concluded that ``ozone depletion occurring in Antarctica is already having an effect on populated regions of the Southern Hemisphere.''