February 28, 2007
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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
STRATOSPHERIC OZONE DECLINE
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
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.
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