Environmental Engineering Reference
In-Depth Information
demand for cereal crops can be expected to rise by about 25% over the
same period. {5.1}
Up to roughly 2°C global warming, studies suggest that crop yield gains
and adaptation measures (especially in higher latitude areas) could balance
yield losses in tropical and other regions, but warming above 2°C is likely to
increase global food prices.
Major increases in trade of food from temperate
to tropical areas are expected as a result of warming and represent one form
of adaptation. Temperate growers are also likely to shift to earlier planting
and longer maturing varieties as climate warms. However, adaptations are
expected to be less effective in tropical regions where soil moisture, rather
than cold temperatures, limits the length of the growing season. Very few
studies have considered the evidence for ongoing adaptations to existing
climate trends and have quantified the benefits of these adaptations. Future
development of new varieties that perform well in hot and dry conditions
may also promote adaptation, but the extent to which this will be effective
remains unclear. At the higher warming scenarios considered in this report,
it will be increasingly difficult to generate varieties with a physiology that
can withstand extreme heat and drought while still being economically
productive. Without adaptation, studies suggest that food prices could more
than double if global warming were to be 5°C. These estimates do not in-
clude additional losses due to weeds, insects, and pathogens, changes in
water resources available for irrigation, effects of increased flood or drought
frequencies, or responses to temperature extremes. {5.1}
Global warming of 2°C would be expected to lead to average yield
losses of U.S. corn of roughly 25% (±16% very likely range) unless effec-
tive adaptation measures are discovered and implemented.
Nearly 40%
of global corn production occurs in the United States, much of which is
exported to other nations. The future yield of U.S. corn is therefore impor-
tant for nearly all aspects of domestic and international agriculture. Higher
temperatures speed development of corn and increase soil evaporation
rates; further warming above 35°C can compromise pollen viability, all of
which reduce final yields. A major challenge in developing drought- and
heat-tolerant varieties is that traits that confer these attributes often reduce
yields in good years. {5.1}
Fire
Wildfire frequency and extent is expected to change in many countries
as the global average temperature increases.
Site-specific studies suggest
that large increases in the area burned are expected in parts of Australia,
