Environmental Engineering Reference
In-Depth Information
Just as there are variations in the vertical
distribution of ozone, there are also variations
in its horizontal distribution. The latter are
seasonal and associated with changing wind and
pressure systems in the lower stratosphere
(Crutzen 1974). Most ozone is manufactured
above the tropics, and is transported polewards
from there. Increased levels of ozone have been
identified regularly at middle and high latitudes
in late winter and spring in the northern
hemisphere (Crutzen 1972), and the
redistribution of ozone by upper atmospheric
winds has been implicated by a number of
authors in the development of the Antarctic ozone
hole (Shine 1988). Such changes have local and
short-term effects which might reinforce or
weaken the global impact of ozone depletion.
Further complications are introduced by the
ability of several of the chemicals which destroy
ozone to interfere directly with the energy flow
in the atmosphere. Ramanathan (1975) has
shown that ozone-destroying CFCs absorb
infrared radiation, and the resulting temperature
increase might be sufficient to negate the cooling
caused by ozone depletion. Similarly, oxides of
nitrogen absorb solar radiation so effectively that
they are able to reduce the cooling caused by their
destruction of ozone by about half (Ramanathan
et al.
1976).
Changes in the earth's energy budget initiated
by declining stratospheric ozone levels are
integrated with changes produced by other
elements such as atmospheric turbidity and the
greenhouse effect. The specific effects of ozone
depletion are therefore difficult to identify, and
the contribution of ozone depletion to climatic
change difficult to assess.
Protection of the Ozone Layer. Twenty nations
signed the Vienna Convention in September
1985, promising international cooperation in
research, monitoring and the exchange of
information on the problem. In the two-year
period between the meetings much time and
effort went into formulating plans to control the
problem, with the countries of the European
Community (EC) favouring a relatively gradual
approach compared to the more drastic
suggestions of the North Americans (Tucker
1987). The Environmental Protection Agency
(EPA) in the United States, against a background
of an estimated 39 million additional cases of
skin cancer in the next century, suggested a 95
per cent reduction in CFC production within a
period of 6-8 years (Chase 1988). When the
Montreal Protocol was signed, participants
agreed to a 50 per cent production cut by the
end of the century, although that figure is
deceptive, since Third World countries were to
be allowed to increase their use of CFCs for a
decade to allow technological improvements in
such areas as refrigeration. The net result turned
out to be only a 35 per cent reduction in total
CFC production by the end of the century, based
on 1986 totals (Lemonick 1987). This was a
historic agreement, but certain experts in the
field, such as Sherwood Rowland, felt that it is
not enough, and that the original 95 per cent
proposed by the EPA was absolutely necessary
(Lemonick 1987).
The signatories to the Montreal Protocol met
again in Helsinki in May 1989. At that time,
along with participants from some 50 additional
countries, they agreed to the elimination of CFC
production and use by the year 2000. Continued
reassessment of the issue led to a further meeting
of the world's environment ministers in
Copenhagen in 1992, at which deadlines for the
control of ozone-destroying gases were revised.
In most cases—CFCs, carbon tetrachloride and
methyl chloroform—production bans were
brought forward from 2000 to 1996, but in the
case of halons the ban was to be implemented by
1994 (see Table 6.2). HCFCs—widely used as
substitutes for CFCs—were to be phased out
THE MONTREAL PROTOCOL
In September 1987, thirty-one countries, meeting
under the auspices of the United Nations
Environment Program in Montreal, signed an
agreement to protect the earth's ozone layer. The
Montreal Protocol was the culmination of a series
of events which had been initiated two years
earlier at the Vienna Convention for the
