Impacts of Climate Change on Agriculture - Climate Resilient Agriculture for Ensuring Food Security - page 67

few years, the World Meteorological Organization
announced in July 2003 that “Recent scientifi c
assessments indicate that, as the global tempera-
tures continue to warm due to climate change, the
number and intensity of extreme events might
increase.”
The frequency of extreme weather events, such
as droughts and fl oods, is predicted to increase.
According to the IPCC, the impacts of climate
change and associated costs will fall dispropor-
tionately on developing countries and may under-
mine the achievement of the global goals of
reducing poverty and safeguarding food security
(IPCC 2001 ). The 2011 drought in the Horn of
Africa, which threatened 12 million people with
malnutrition, disease, and loss of livelihoods, is a
recent example of an extreme weather event. As
such events become more frequent, the number of
vulnerable or directly affected people will increase.
The balance between profi t and loss in com-
mercial farming often depends on the relative fre-
quencies of favorable and adverse weather; for
example, on the Canadian prairies, a major con-
straint on profi table wheat production is related
to the probability of the fi rst autumn frost occur-
ring before the crop matures (Robertson 1970 ).
Changes in rainfall could have a similarly
magnifi ed impact. For example, if mean rainfall
in the Corn Belt in March (which is about
100 mm) decreased by 10 % (an amount pro-
jected by some GCMs under a 2xCO 2 climate),
this would raise the probability of less than
25 mm being received by 46 %. For cattle, crops,
and trees, a 1 % reduction in rainfall could mean
that drought-related yield losses increase by as
much as a half (Waggoner 1983 ).
Sequential extremes can affect yields and
disease patterns. Droughts, followed by intense
rains, for example, can have an impact on soil
water absorption, increasing the potential for
fl ooding that creates conditions favoring fungal
infestations of leaves, roots, and tuber crops.
Prolonged anomalous periods - such as the 5
years of El Niño conditions between 1990 and
1995 - can also have destabilizing affects on
agriculture.
Sequential extremes, along with altered tim-
ing of seasons, may also decouple long-evolved

relationships among species (e.g., predator/prey)
essential for controlling pests and pathogens as
well as populations of plant pollinators.
Strong winds can cause leaf and limb damage,
as well as “sand blasting” of the soil against the
foliage. Heavy rains that often result in fl ooding
can also be detrimental to crops and to soil struc-
ture. Most plants cannot survive in prolonged
waterlogged conditions because the roots need to
breathe. In addition, fl ooding can erode top soil
from prime growing areas, resulting in irrevers-
ible habitat damage. Heavy winds combined with
rain (from events such as hurricanes and torna-
does) can down large trees and damage houses,
barns, and other structures involved in agricul-
tural production.
Considerations of the potential impacts of cli-
mate change on agriculture should, therefore, be
based not only on the mean values of expected cli-
matic parameters but also on the probability, fre-
quency, and severity of possible extreme events.

4.6.1 Extreme Temperatures

Meteorological records suggest that heat waves
became more frequent over the twentieth century,
and while individual events cannot be attributed
to climate change, the change in probability of a
heat wave can be attributed. Europe experienced
a particularly extreme climate event during the
summer of 2003, with average temperatures 6 °C
above normal and precipitation defi cits of up to
300 mm. A record crop yield loss of 36 %
occurred in Italy for corn grown in the Po Valley
where extremely high temperatures prevailed
(Ciais et al. 2005 ). It is estimated that such sum-
mer temperatures in Europe are now 50 % more
likely to occur as a result of anthropogenic cli-
mate change. In 1972, extremely high summer
average temperature in the former Soviet Union
(USSR) contributed to widespread disruptions in
world cereal markets and food security.
Changes in short-term temperature extremes
can be critical, especially if they coincide with
key stages of development. Only a few days of
extreme temperature (greater than 32 °C) at the
fl owering stage of many crops can drastically