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Increasing UV-B Exposure in Temperate Climates

The effects of chlorofluorocarbons on decreasing the ozone content of the stratosphere, thereby increasing ultraviolet-B exposure at the surface of the Earth, has generated much concern among dermatologists and the lay public. The implication of increased UV-B exposure is that there would likely be an increased incidence of basal cell carcinomas, squamous cell carcinomas, and, possibly, melanomas. Although the reduction in stratospheric ozone is well documented, there is no definitive evidence that UV-B exposure has increased anywhere but in Antarctica. In fact, some scientists argue that air pollution and clouds negate the effects of ozone loss; therefore, no action need be taken to stem the loss of ozone.

Two scientists now present compelling evidence for an increase in UV-B exposure during a recent four-year period in Canada. Using highly sensitive and calibrated instruments, they measured daily UV-B exposure at a single site in Toronto from 1989 to 1993. To distinguish between the UV-B blocking effects of ozone and the "non-specific" UV-B blocking effects of clouds, haze and pollutants, the investigators measured UV-B intensity at each of its component wavelengths. Ozone blocks UV-B radiation at 300 nm but not at 325 nm, whereas clouds, haze, and pollutants block UV-B radiation at both wavelengths.

The intensity of UV-B at 300 nm increased by 35% per year in the winter and 7% per year in the summer. There was no change in intensity of UV-B at 325 nm, demonstrating that the increase in UV-B at 300 nm was consistent with a loss of ozone. During the same period ozone concentrations over Toronto decreased by 4% per year in winter and by 1.8% per year in summer.

Comment: This paper provides very specific evidence that UV-B exposure is rising in temperate climates, most likely caused by the loss of ozone. Like any good scientific discovery, this work should be repeated and extended over a longer time period. Unfortunately, if we wait too long to accept the risks of chlorofluorocarbons, it may be too late to effect a solution to the problem.

— PA Bleicher

Published in Journal Watch Dermatology January 1, 1994

Citation(s):

Kerr JB; McElroy CT. Evidence for large upward trends of ultraviolet-B radiation linked to ozone depletion. Science 1993 262 1032 -1034.

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