Agriculture Reference
In-Depth Information
CHAPTER THIRTY-FOUR
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C
limate Change, Global Warming,
a
nd Agricultural Droughts
G
ENNADY V. MENZHULIN, SERGEY P. SAVVATEYEV,
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Norm
PgEn
The climate of a region is a representation of long-term weather conditions
that prevail there. Over the millions of years of the existence of the atmo-
sphere on the earth, the climate has changed all the time; ice ages have
come and gone, and this has been the result of natural causes. Recently (on
geological time scales) the human population has expanded—from half a
billion in 1600, to 1 billion in 1800, to almost 3 billion in 1940, and it
now stands at about 6 billion. The climate may well now be influenced not
only as before by natural events but also by human activities. For example,
we are producing vast amounts of carbon dioxide by burning fossil fuels,
and this is causing the temperature of the earth to rise significantly. If we
argue that we should control our activities to preserve this planet as a hab-
itable environment for future generations, we need to have some scientific
knowledge of the effects of our present activities on climate.
In recent years the evidence has been accumulating that on the time
scale of decades there is global warming (i.e., the global annual mean
surface temperature is increasing). There is also evidence accumulating that
part of this increase is a consequence of human activities. The evidence
is largely statistical. Within this trend there are bound to be temporal
fluctuations and spatial variations. Moreover, in addition to the increase
in temperature, it is reasonable to assume that there is, overall, an increase
in evaporation of water from the surface of the earth and that there will
be a consequent increase in precipitation. But within this overall scenario
there are bound to be local variations; some areas may experience more
precipitation, but some areas may experience less precipitation. The effect
of climate change on the proneness to drought is therefore not uniform
but can be expected to vary from place to place. Therefore, whether one is
concerned with considering the relation between climate and proneness to
drought from the historical evidence or whether one is trying to use models
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