Environmental Engineering Reference
In-Depth Information
aerosols influence precipitation processes,
because of their ability to act as condensation
nuclei. The extent and direction of that influence
is largely unknown. A general consensus
appeared to emerge in the mid-1980s, that
changes in climate brought on by increasing
aerosol concentrations have been relatively
minor, taking the form of a slight warming rather
than the cooling postulated a decade earlier. It is
entirely possible, however, that in the event of a
significant global temperature reduction at some
time in the future, atmospheric turbidity will be
resurrected as a possible cause. The development
of new, improved GCMs will help to provide
information on the climatic effects of atmospheric
aerosols, but it is recognized by the World
Meteorological Organization, and a number of
other international scientific and environmental
groups, that direct atmospheric observation and
monitoring is essential if the necessary aerosol
climatology is to be established (Kellogg 1980;
Bolle
et al.
1986).
Once into the atmosphere, they are redistributed
by way of the wind and pressure patterns,
remaining in suspension for periods ranging from
several hours to several years, depending upon
particle size and altitude attained. The presence
of aerosols disrupts the inward and outward flow
of energy through the atmosphere. Studies of
periods of intense volcanic activity suggest that
the net effect of increased atmospheric turbidity
is cooling, and some of the coldest years of the
Little Ice Age—between 1430 and 1850—have
been correlated with major volcanic eruptions.
Aerosols produced by human activities cannot
match the volume of material produced naturally,
but, in the 1960s and early 1970s, some studies
suggested that the cumulative effects of relatively
small amounts of anthropogenic aerosols could
also cause cooling. Present opinion sees
atmospheric turbidity actually producing a slight
warming. The greatest problem in the study of
the impact of atmospheric turbidity on climate
is the scarcity of appropriate data and that
situation can only be changed by the introduction
of systematic observation and monitoring, to
complement the theoretical analysis—based on
atmospheric modelling techniques—which has
been developed in recent years.
SUMMARY
Particulate matter has undoubtedly been a
constituent of the atmosphere from the very
beginning, and natural processes which existed
then continue to make the major contribution to
atmospheric turbidity. Volcanic activity, dust
storms and a variety of physical and organic
processes provide aerosols which are
incorporated into the gaseous atmosphere.
Human industrial and agricultural activities also
help to increase turbidity levels. The aerosols vary
in size, shape and composition from fine chemical
crystals to relatively large, inert soil particles.
SUGGESTIONS FOR FURTHER READING
Royal Meteorological Society (1992) 'Gulf War
Meteorology: Special Issue',
Weather
47(6),
London: Royal Meteorological Society.
Sagan, C. and Turco, R. (1990)
A Path Where
No
Man Thought: Nuclear Winter and the
End of the Arms Race,
New York: Random
House.
