Agriculture Reference
In-Depth Information
change productivity and increase risks. To address
these changes, some production systems may
need to be relocated. Impacts on postharvest
activities, on value addition, and on the distribu-
tion of fi sh to local, national, and global markets
may also be signifi cant, with potential changes
in location and variability of supplies and changes
in access to other key inputs, such as energy and
water for processing.
Indications suggest that pests, such as aphids
(Newman 2004 ) and weevil larvae, respond posi-
tively to elevated CO 2 . Increased temperatures
also reduced the overwintering mortality of
aphids, enabling earlier and potentially more
widespread dispersion. Evidence suggests that in
sub-Saharan Africa migration patterns of locusts
may be infl uenced by rainfall patterns, and thus
potential exists for climate change to shape the
impacts of this devastating pest. Pathogens and
diseases may also be affected by a changing
climate. This may be through impacts of warming
or drought on the resistance of crops to specifi c
diseases and through the increased pathogenicity
of organisms by mutation induced by environ-
mental stress (Gregory et al. 2009 ). Over the next
10-20 years, disease affecting oilseed rape could
increase in severity within its existing range as
well as spread to more northern regions where at
present it is not observed.
Because climate variables (especially tempera-
ture, wind, and humidity) control the geographic
distribution of pests, climate change is likely to
alter their ranges. Insects may extend their ranges
where warmer winter temperatures allow their
overwintering survival and increase the possible
number of generations per season (Stinner et al.
1989 ). Pests and diseases from low-latitude
regions, where they are much more prevalent,
may be introduced at higher latitudes. As a conse-
quence of pest increase, there may be a substantial
rise in the use of agricultural chemicals in both
temperate and tropical regions to control them.
4.9
Pests, Diseases, and Weeds
Climate affects not just agricultural crops but their
associated pests (weeds, insects, and pathogens)
as well. The distribution and proliferation of
weeds, fungi, and insects are determined to a large
extent by climate. Organisms become pests when
they compete with, or prey upon, crop plants or
cause disease in crop plants to an extent that
reduces productivity. Not only does climate affect
the type of crops grown and the intensity of the
pest problems, it affects the pesticides often used
to control or prevent outbreaks. The intensity of
rainfall and its timing with respect to pesticide
application are important factors in pesticide
effectiveness, persistence, and transport.
As temperature increases, the pests will
become more abundant through a number of
interrelated processes, including range exten-
sions and phenological changes, as well as
increased rates of population development,
growth, migration, and overwintering. The cli-
mate change is likely to alter the balance
between pests, their natural enemies, and their
hosts. The rise in temperature will favor pest
development and winter survival. Rising atmo-
spheric carbon dioxide concentrations may
lead to a decline in food quality for plant-feed-
ing insects, as a result of reduced foliar nitro-
gen levels. The epidemiology of plant diseases
will be altered. The prediction of disease out-
breaks will be more diffi cult in periods of rap-
idly changing climate and unstable weather.
Environmental instability and increased inci-
dence of extreme weather may reduce the
effectiveness of pesticides on targeted pests or
result in more injury to nontarget organisms.
4.10
UV-B Radiation
One class of atmospheric trace gases, the
chlorofl uorocarbons (CFCs), has an important
additional effect on the atmosphere; their photo-
degradation products act to destroy ozone (O 3 ) in
the stratosphere. Ozone is a strong absorber of
solar ultraviolet radiation, and the stratospheric
ozone layer acts to fi lter out much of the ultravio-
let component of the solar spectrum before it
penetrates to the earth's surface. Thus, depletion
of stratospheric O 3 allows more solar UV to reach
the earth's surface.
 
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