Environmental Engineering Reference
In-Depth Information
increased to 112 in 2008. It is expected to be 2080 before full recovery
occurs.
Because CFCs are used in a wide range of products, a substitute for
them is essential. The replacement chemicals are hydrofl uorocarbons
(HFCs). They lack the chlorine atoms so deadly to the ozone layer but
nevertheless are potent heat-trapping substances. Because they are
released in tiny traces, they currently contribute less than 1 percent of
the climate-warming effect of the carbon dioxide we produce. However,
a recent analysis published by the National Academy of Sciences notes
that the fast-paced growth in the use of HFCs in developing countries
will soon make them a far bigger contributor to global warming than
they now are.
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Pound for pound, HFCs are hundreds to thousands of
times more powerful ozone destroyers than carbon dioxide. By midcen-
tury, emissions of HFCs could surge to cause global warming equivalent
to the impact of between 28 and 45 percent of emissions of carbon
dioxide.
Methyl Bromide
Methyl bromide is a broad-spectrum and very effective pesticide used to
control pest insects, nematode worms, weeds, pathogens, and rodents.
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Like CFCs, the chemical rises into the atmosphere and attacks the ozone
layer. About 21,000 tons have been used annually in agriculture, primar-
ily for soil fumigation (85 percent). Globally, about 72,000 tons are used
annually, with use in North America the highest (38 percent), followed
by Europe (28 percent), Asia and the Middle East (22 percent), and
Africa and South America (12 percent).
Between 50 and 95 percent of the methyl bromide injected into
the soil to sterilize it can eventually enter the atmosphere. In the
United States, California strawberries and Florida tomatoes are the
crops that use the most methyl bromide. Other crops that use this
pesticide as a soil fumigant are tobacco, peppers, grapes, and nut and
vine crops.
Production and importation of methyl bromide were scheduled to end
in 2005 in the developed nations but have been delayed for lack of a
suitable substitute. Developing countries have until 2015. There is no
single alternative for all the functions of the chemical, and many different
chemicals must be used to do the work it has been performing, which
increases a farmer's costs and also the time spent in planting and growing
the crop.
