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A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 6, NUMBER 6, JUNE 1993

NEWS...
STRATOSPHERIC OZONE DECLINE

Item #d93jun76

Satellite measurements published by NASA scientists in April show that ozone amounts, averaged over most of the globe, dropped two to three percent during 1992, falling clearly below the range of values observed since 1979. Levels have remained low through the first few months of 1993. Volcanic particles from the 1991 eruption of Mount Pinatubo are considered a likely cause of the decline, either through chemical reactions involving anthropogenic chlorine compounds, or through the effects of the particles on stratospheric wind patterns. However, the results reported differ from expectations of the effect of Pinatubo's dust on ozone levels, and this explanation remains unproven. (See Science, pp. 490-491, Apr. 23 1993; Science News, p. 260, Apr. 24 1993; Chem. Eng. News, p. 8, Apr. 26 1993 and pp. 8-18, May 24 1993; Science News, p. 8, May 1 1993.)

Other research reported by workers from the Jet Propulsion Laboratory of the California Institute of Technology shows that chlorine in the winter polar stratospheres of both hemispheres is almost completely converted to ozone-destroying forms, leading them to conclude that ozone depletion by chlorine compounds is of greater concern than previously thought. Another study provides a mechanism explaining why volcanic eruptions do not contribute significant amounts of chlorine to the atmosphere. This finding supports the idea that human activities, not natural processes, are mainly responsible for ozone depletion. (See New Scientist, p. 16, June 5 1993).

A lengthy feature article in Chemical and Engineering News discusses the discrepancy between a growing popular perception that the ozone depletion problem has been solved, and current scientific understanding. (See "Ozone Depletion's Recurring Surprises Challenge Atmospheric Scientists," P.S. Zurer, pp. 8-18, May 24 1993.) It cites some recent popular books, talk show discussions and newspaper articles which suggest the problem has been brought under control by present agreements under the Montreal Protocol, or that there never was a problem at all. The article contrasts these views with the feeling of most scientists that the ozone depletion situation is not fully understood, and could still hold some surprises before anthropogenic chlorine starts declining as a result of the Montreal Protocol. It substantiates this view with an extensive summary of several major "shocks" to scientific understanding in the past, starting with the recognition of the Antarctic ozone hole in 1985, and summarizes the latest understanding and remaining questions. The article describes in detail how long-time ozone researcher James Rowland, who is very concerned about communication of scientific understanding to the public, refutes some myths commonly used as arguments to downplay the ozone problem.

One of the more moderate recent popular presentations is a front-page article in the Washington Post ("Outlook for the Ozone Layer Looks Good," B. Rensberger, Apr. 15). While not dismissing the reality of ozone depletion, it states that scientists expect the threat to peak in just seven years as a result of provisions of the Montreal Protocol. The article quotes two prominent scientists (Michael Oppenheimer of the Environmental Defense Fund and Richard Stolarski of NASA) who believe that ozone depletion does not appear to be a catastrophe.