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Introduction
During the past century, human activities have caused increases
in the atmospheric concentrations of both naturally occurring and
artificially introduced "greenhouse" gases. The carbon dioxide
(CO2) concentration, for example,
has increased about 25 percent. Currently, these long-lived gases,
some of which are more effective than others at trapping heat,
combine to provide an increase in greenhouse warming over the past
100 years equivalent to that which would have been provided by a 40
percent increase in CO2 alone.
The highly publicized concern that these greenhouse gas
accumulations might lead to a significant modification of the
earth's climate underlies an expanding body of literature. Much of
this work deals with quantitative discussions of the greenhouse gas
accumulation itself, quantitative analyses of the heat balance of
the planet, and inferences from these analyses for climate change.
Part Two of this report has been written by the Effects Panel with
a full awareness of the deliberations that have led to much of the
greenhouse warming literature, and its assessments rest on the same
foundations as do several other assessments of the same
questions.1 It was not the panel's
purpose to retrace these steps, but rather to assess this body of
knowledge in terms of policy needs.
The panel first examined the climate record and the difficulties
associated with its interpretation, as well as the available
analytical tools and their limitations. It then developed a
concise, objective account of the current knowledge, understanding,
and predictive capability that attend the greenhouse warming
question. The panel made no attempt to perform a comprehensive
critical assessment from the perspective of the various relevant
scientific disciplines. The report of the Intergovernmental Panel
on Climate Change (1990) is comprehensive and covers in greater
detail the topics that
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are addressed in the report of the Effects Panel. The Effects
Panel's report is more constrained in scope and presents a succinct
representation of data and knowledge to serve as a backdrop for
current policy decisions. In doing so, it examines in depth only a
few topics that illustrate the extent to which the current science
base is sufficient to inform policy decisions. The panel believes
the principal difference between its analysis and that of the IPCC
is that in the Effects Panel's analysis a greater credence is
accorded to the uncertainties in the current scientific knowledge
and tools.
The task assigned to the Effects Panel did not require it to
assess policy issues as such. Nevertheless, its members record here
their support of the conclusions, including the need for prudent
response, that are expressed in the report of the Synthesis Panel
(Part One).
Note
1. See, for example, Intergovernmental Panel on Climate Change,
1990; U.S. Congress, Office of Technology Assessment, 1991; and
National Research Council, 1983.
References
Intergovernmental Panel on Climate Change. 1990. Climate Change:
The IPCC Scientific Assessment, J. T. Houghton, G. J. Jenkins, and
J. J. Ephraums, eds. New York: Cambridge University Press.
National Research Council. 1983. Changing Climate: Report of the
Carbon Dioxide Assessment Committee. Washington, D.C.: National
Academy Press.
U.S. Congress, Office of Technology Assessment. 1991. Changing
by Degrees: Steps to Reduce Greenhouse Gases. OTA-O-482.
Washington, D.C.: U.S. Government Printing Office.
Representative terms from entire chapter:
greenhouse gas
