Environmental Engineering Reference
In-Depth Information
around the world, the IPCC produced the first
part of its report—the scientific assessment—in
1990 (Houghton
et al.
1990). The reports on
impact assessment (Tegart
et al.
1990) and
response strategies (IPCC 1991) followed shortly
thereafter. The scientific assessment included a
summary of current knowledge of global
warming as well as predictions for future
developments (see Table 7.2). A supplementary
report was issued in 1992, generally confirming
the results of the earlier assessment, but also
paying greater attention to the effects of sulphate
emissions and ozone depletion on global warming
trends (Houghton
et al.
1992).
Concern over global warming was also an
integral part of the Framework Convention on
Climate Change signed at the Earth Summit in
Rio de Janeiro in 1992. The convention was
intended to deal with the human contribution to
global warming, and create a vehicle for
international action comparable to the Montreal
Protocol on ozone depletion. For most observers,
however, it was no more than a symbolic
statement with few specific targets and no proper
enforcement mechanisms (Clery 1992; Hulme
1993). The refusal of the United States to agree
to even modest greenhouse gas emission targets,
and the unwillingness of some Third World
countries to support the energy efficiency
standards necessary for reduced emissions,
further weakened the convention (Pearce 1992c).
The perceived weakness of the convention is
in part a reflection of the different views of the
issue held by policymakers and scientists (Leggett
1992). Despite the immense volume of research
on global warming, many key elements—such
as the magnitude and timing of the warming—
remain imperfectly understood, and therefore
difficult to predict with any accuracy. Uncertainty
of this type is not uncommon in scientific
research, and scientists have come to accept it,
but among planners and politicians it is often
seen as undermining the arguments of those
calling for immediate attention to the issue. Since
policymakers have the ultimate say in where and
when policy will be implemented to deal with
the warming, it appears that they must shoulder
much of the blame for the delays. However, some
environmentalists also claim that scientists have
failed, by giving too much attention to the
uncertainties and too little to the dire
consequences of full-scale warming (Leggett
1992).
No matter how the blame is apportioned, one
of the results of the uncertainty has been to allow
those who remain unconvinced by the scientific
assessment, or perhaps have a vested interest in
retaining the
status quo,
to argue successfully that
no steps be taken to deal with the issue until the
real impact of global warming is revealed by
additional research. That may yet take several
decades, and some of the researchers investigating
the problem warn that by then it may be too late
(Roberts 1989; Henderson-Sellers 1990).
Atmospheric carbon dioxide and temperature
change
Although present concern with global warming
centres on rising concentrations of atmospheric
CO
2
, concentrations of that gas have varied
considerably in the past. Analysis of air bubbles
trapped in polar ice indicates that the lowest
levels of atmospheric CO
2
occurred during the
Quaternary glaciations (Delmas
et al.
1980). At
that time, the atmosphere contained only 180 to
200 parts per million by volume (ppmv) of CO
2
,
although there is some evidence that levels
fluctuated by as much as 60 ppmv in periods as
short as 100 years (Crane and Liss 1985). Levels
rose to 275 ppmv during the warm interglacial
phases, and that level is also considered
representative of the pre-industrial era of the early
nineteenth century (Bolin 1986). CO
2
measurements taken by French scientists in the
1880s, just as the effects of the Industrial
Revolution were beginning to be felt, have been
reassessed by Siegenthaler (1984), who has
concluded that levels in the northern hemisphere
averaged 285 to 290 ppmv at that time.
When the first measurements were made at
Mauna Loa in 1957, concentrations had risen
to 310 ppmv, and they continued to rise by just
over 1 ppmv per year to reach 335 in 1980.
