Shaky Science Scarier Than Ozone Fiction

Article excerpt

During the past five years, the public has been bombarded with alarming news about an alleged depletion of the stratospheric ozone layer that shields the Earth's surface against solar ultraviolet radiation. This is especially scary because part of the ultraviolet spectrum, termed UV-B, is believed to cause skin cancer, including the deadly malignant melanoma, and a variety of other disasters luridly spelled out in the popular press: plankton death, blind sheep and rabbits and, of course, the obligatory effect on the immune system.

The trouble is that the existing scientific evidence has not supported the more frightening scenarios. Plankton have such a short life cycle that populations affected by any increase in UV-B would be expected to adapt quickly. Blind sheep in southern Chile were found to have common eye infections in no way associated with any putative increases in UV-B. And any serious effect on the immune system from an increase in ultraviolet radiation surely would have been seen already among all those New Yorkers who've retired and moved to Florida in recent years. Because of the higher angle of the sun, just moving from New York to Miami increases UV-B exposure by more than 200 percent!

Nevertheless, the precipitous acceleration of the chlorofluorocarbon phaseout, rammed through Congress in February 1992 on the basis of a nonexistent "ozone hole over Kennebunkport," will cause serious adjustment problems. The crunch may come as early as this summer, as motorists pay to recharge their auto air conditioners.

Two recently published studies underscore the shaky science that has been used to support recent efforts to eliminate production of important chemicals like halons, methyl bromide, carbon tetrachloride, as well as chlorofluorocarbons, or CFCs. One study received wide attention; the other is almost unknown to the general public.

In November 1993, the journal Science featured an article by two Canadian researchers, James Kerr and Thomas McElroy, titled "Evidence Large Upward Trends of Ultraviolet-B Radiation Linked to Ozone Depletion." The Kerr-McElroy paper received extensive newspaper and television coverage as the result of a press release issued by Science before the paper appeared in print. The media focused on the authors' claim to have detected a 35 percent per year increase in surface ultraviolet radiation in the winters between 1989 and 1993, and their contention that the large upward trends of surface UV were due to the depletion of stratospheric ozone over populated regions of North America.

Both findings are incorrect. In fact, the study was so flawed that my colleague Patrick Michaels of the University of Virginia and I have taken the unprecedented step of asking the editors of Science to withdraw the paper and issue a correction.

To begin, the results quoted did not show error bars (margins of error defining the uncertainty), which invariably are attached to every scientific result. When Michaels repeated the statistical analysis at the Virginia State Office of Climatology, using the Canadian data, the margins of error were found to be so large as to cancel out most, if not all, of the claimed increases. …