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OCR for page 1
Introduction
Two important climatic issues-stratospheric ozone depletion
and greenhouse gas increase-and the apparent connection between
them led to the holding of this symposium. Theory predicts that
ozone depletion should be occurring as a result of chIorofluorocarbons
and haloes in the stratosphere. Recent measurements confirm that
such depletion is taking place on a global scale and is especially pro-
nounced in the antarctic stratosphere. Global tropospheric warming
due to increasing greenhouse gases has been an important climatic
issue for many years, and several symposia and workshops have pre-
viously been held on this topic. However, recent data have made it
increasingly apparent that the projected increase in greenhouse gases
and the associates! tropospheric warning and stratospheric cooling
will indirectly affect ozone concentrations in the stratosphere, which
in turn will affect tropospheric climatic conditions. Thus, the two
issues are inextricably entwined and form part of the larger global
change issue that recognizes that essentially all components of the
earth-atmosphere-ocean-biosphere-cryosphere system interact with
and affect one another, often in ways that are currently not well
understood.
This symposium was primarily concerned with the linkages be-
tween ozone depletion and increasing greenhouse gases and with their
combined effect in causing climate change to occur on a global scale.
The presentations in these proceedings review the current state of
1
OCR for page 2
2
INTRODUCTION
knowledge about stratospheric ozone depletion, discuss the probable
effect of predicted greenhouse gas increase on future ozone trends,
summarize observational data on changing atmospheric chemistry
and associated atmospheric temperatures, and describe the contin-
uing effort to mode} and predict future scenarios of climatic change
relative to ozone and greenhouse gases in both the stratosphere and
the troposphere. Some of the questions and answers that followed
the presentations have been included when they highlight noteworthy
points that were not covered in the presentation itself. The request
by the National Climate Program Office for a symposium on the
above related issues is included as Appendix A, and the symposium
agenda and participants are given in Appendix B. Appendix C is a
glossary of special terms and abbreviations.
The first presentation, by William C. Clark, provides an overview
of the global change issue and indicates the role of the symposium in
furthering the goals of that larger effort. Daniel L. Albritton discusses
the observational ant! analytical information on stratospheric ozone
depletion that led to the signing of the September 1987 Montreal
international agreement to restrict the input of ozone-destroying
halocarbons into the atmosphere. Robert T. Watson's presentation
describes the evidence for an antarctic stratospheric ozone "hole"
and indicates that chlorine compounds are implicated as the primary
cause of this phenomenon.
In his paper, F. Sherwood Rowland discusses the long-term out-
look for stratospheric halocarbon concentrations and the associated
outlook for ozone concentrations. He also presents evidence of recent
stratospheric ozone depletion in the Northern Hemisphere, espe-
cially in winter. Mario J. Molina describes the specific heterogeneous
chemical processes, believed to occur in the polar stratosphere, that
result in the efficient destruction of ozone by free chlorine atoms and
chlorine oxides. James G. Anderson discusses the less efficient ho-
mogeneous ga~phase catalytic process that destroys ozone elsewhere
in the stratosphere. Anderson also presents additional evidence that
shows why heterogeneous processes are especially efficient when ice
clouds form in the polar stratospheric regions.
Jerry D. MahIman reviews the combined effect of trace gases on
changing stratospheric temperatures and circulation. MahIman indi-
cates that these stratospheric changes will feed back on the behavior
of the trace gases and on the concentration of ozone, necessitat-
ing the use of dynamic modeling in order to fully understand and
accurately predict the changes that will occur. Robert C. Harriss
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INTROD LOTION
3
discusses the outlook for increased concentrations of one of the trace
gases, methane, that affects stratospheric ozone chemistry and is also
a tropospheric greenhouse gas. Harriss indicates that the extensive
peat bogs and marshlands of the arctic slope are likely to be prime
sources of increased atmospheric methane as the climate warms, pro-
viding a positive feedback for tropospheric warning and affecting
stratospheric ozone distribution.
Kevin E. Trenberth reviews the evidence for global temperature
trends, including both tropospheric warming and stratospheric cool-
ing. Trenberth notes that the short duration of reliable stratospheric
records along with other data problems makes it especially difficult
to establish unambiguous temperature trends in the stratosphere. In
the last paper, Robert E. Dickinson reviews the progress made with
- general circulation models in predicting the likely climatic changes
engendered by increasing greenhouse gases and indicates those as-
pects of the climate system that are critical and in need of further
mode! development.
In summary, the Joint Symposium on Ozone Depletion, Green-
house Gases, and Climate Change reviewed the magnitude and causes
of stratospheric ozone depletion and examined the connections that
exist between this problem and the impending climate warming due
to increasing greenhouse gases. The presentations of these proceed-
ings indicate that the connections are real and important and that
the stratospheric ozone depletion and tropospheric greenhouse warm-
ing problems must be studied as parts of an interactive global system
rather than as more or less unconnected events.
Representative terms from entire chapter:
stratospheric ozone