Environmental Engineering Reference
In-Depth Information
and improve its quality of life, yet success might
lead to a thinning of the ozone layer with
consequent climatic change and biological
damage from increased ultraviolet radiation. If
monitoring does reveal that N 2 O emissions are
increasing, some extremely difficult judgements
will have to be made; judgements which could
have a far greater impact than the grounding of
SSTs or the banning of CFCs from use in aerosol
spray cans.
the basic foundations of life, such as the DNA
molecule and various proteins (Crutzen 1974).
They also inhibit photosynthesis. Growth rates
in plants such as tomatoes, lettuce and peas are
reduced, and experimental exposure of some
plants to increased ultraviolet radiation has
produced an increased incidence of mutation
(Hammond and Maugh 1974). Insects, which
can see in the ultraviolet sector of the spectrum,
would have their activities disrupted by
increased levels of ultraviolet radiation
(Crutzen 1974).
Most of the concern for the biological effects
of declining ozone levels has been focused on
the impact of increased ultraviolet radiation on
the human species. The potential effects include
the increased incidence of sunburn, premature
ageing of the skin among white populations and
greater frequency of allergic reactions caused by
the effects of ultraviolet light on chemicals in
contact with the skin (Hammond and Maugh
1974). These are relatively minor, however, in
comparison to the more serious problems of
skin cancer and radiation blindness, both of
which would become more frequent with higher
levels of ultraviolet radiation. Skin cancer had a
prominent role in the SST and CFC debates of
the 1970s (Dotto and Schiff 1978), and it
continues to evoke a high level of concern. The
number of additional skin cancers to be
expected as the ozone layer thins is still a matter
of debate, but a commonly accepted estimate is
that a 1 per cent reduction in ozone allows an
increase in UV-B of 1-2 per cent. This in turn
leads to a 2-4 per cent increase in the incidence
of non-melanoma skin cancers (Concar 1992).
Hammond and Maugh (1974) have suggested
that a 5 per cent reduction in ozone levels would
cause an additional 20,000 to 60,000 skin
cancers in the United States alone. The US
National Academy of Sciences has also
estimated that a 1 per cent decline in ozone
would cause 10,000 more cases of skin cancer
per year (Lemonick 1987). Many skin cancers
are non-malignant and curable, but only after
painful and sometimes disfiguring treatment. A
relatively small proportion—the melanomas—are
THE BIOLOGICAL AND
CLIMATOLOGICAL EFFECTS OF
CHANGING OZONE LEVELS
Declining concentrations of stratospheric
ozone allow more ultraviolet radiation to reach
the earth's surface. Even after a decade and a
half of research, the impact of that increase is
still very much a matter of speculation, but
most of the effects which have been identified
can be classified as either biological or
climatological.
Biological effects.
In moderate amounts ultraviolet radiation has
beneficial effects for life on earth. It is a powerful
germicide, for example, and triggers the
production of Vitamin D in the skin. Vitamin D
allows the body to fix the calcium necessary for
proper bone development; lack of it may cause
rickets, particularly in growing children. High
intensities of ultraviolet radiation, however, are
harmful to all forms of life.
Lifeforms have evolved in such a way that
they can cope with existing levels of ultraviolet
radiation. They are also quite capable of
surviving the increases in radiation caused by
short-term fluctuations in ozone levels. Most
organisms would be unable to cope with the
cumulative effects of progressive thinning of the
ozone layer, however, and the biological
consequences would be far-reaching.
The most serious concern is over rising levels
of UV-B—the radiation recognized as causing
most biological damage. Intense UV-B rays alter
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