IMPACTS ON AGRICULTURE
(A Canadian Perspective)
"Climate change will impact agriculture by causing damage and
gain at scales ranging from individual plants or animals to global trade networks.”
Impacts on Crops
Climate change will potentially have many impacts on
agricultural production (Figure 1). As such, there is great variation in
projections of crop response to climate change, with both gains and losses
commonly predicted. Several recent Canadian studies have integrated crop models
with general circulation model (GCM) output for a 2xCO2 climate scenario, in
order to project the impact of climate change on different
types of crops. Examples include:
• McGinn et al. who suggested that yields of canola, corn
and wheat in Alberta
would increase by between 21 and 124%.
• Singh et al., who suggested that corn and sorghum yields
in Quebec
could increase by 20%, whereas wheat and soybean yields could decline by
20–30%. Canola, sunflowers, potatoes, tobacco and sugarbeets are expected to
benefit, while a decrease in yields is anticipated for green peas, onions,
tomatoes and cabbage.
• Bootsma et al., who suggested that there could be an
increase in grain corn and soybean yields in the Atlantic Provinces by 3.8 and
1.0 tonnes/hectare respectively, whereas barley yields are not expected to
experience significant changes. They further suggested that a minimum of 50% of
the agricultural land area presently seeded to small grain cereals and silage
corn may shift production to grain corn and soybeans to maximize
economic gains.
As with other sectors, concerns exist about the resolution
of GCM output when modelling agricultural impacts. Many studies interpolate GCM
data to obtain regional projections of future changes in climate. Questions
have been raised about the validity of the interpolation methods and the
accuracy of the results, especially for regions with specific microclimates
(e.g., Niagara Peninsula,
Annapolis Valley). With respect to methodology,
however, a recent statistical study concluded that differences in the
downscaling methods used to address scale issues do not unduly influence study
results, thereby increasing general confidence in model projections.
Increased moisture stress and drought are major concerns for
both irrigated and non-irrigated crops across the country. If adequate water is
not available, production declines and entire harvests can be lost. While
climate change is expected to cause moisture patterns to shift, there is still
considerable uncertainty concerning the magnitude and direction of such
changes. Furthermore, longer growing seasons and higher temperatures would be expected
to increase demand for water, as would changes in the frequency of drought. Boxes 1 and 2
describe the results of recent studies that examined how climate change may
affect moisture conditions in the Prairies and the Okanagan
Valley, two of the driest agricultural
regions of Canada.
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BOX 1:
Will the Prairies become drier?
Will moisture deficits and drought increase in the future due to climate
change? This is a key question for the Prairie
Provinces, where moisture constraints are already a
large concern and recurrent drought results in substantial economic losses in
the agricultural community. Unfortunately, a clear answer to this question
remains elusive.
Using the Canadian Centre for Climate Modelling and Analysis coupled
General Circulation Model (CGCM1), Nyirfa and Harron found that moisture
limitations would be significantly higher over much of the Prairies'
agricultural regions by 2040-2069. Although precipitation is expected to
increase, it will not be sufficient to offset increased moisture losses from
warmer temperatures and increased rates of evapotranspiration. As a result, the
researchers believe that spring-seeded small grain crops will be threatened
unless adaptations, such as cropping changes and shifts in pasture areas, are
undertaken.
In contrast, using a range of climate change scenarios, McGinn et al.
found that moisture levels in the top 120 cm of the soil profile would be the
same or higher than present-day values. Their models also suggested that the
seeding dates for spring wheat will be advanced by 18-26 days, and that the
growing season will be accelerated. This would allow crops to be harvested
earlier in the year, thereby avoiding the arid conditions of late summer.
However, the benefits are not expected to be felt evenly across the Prairies;
there are regions of concern, such as southeastern Saskatchewan
and southern Manitoba,
where summer precipitation is projected to decrease.
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BOX 2:
Water supply and demand in the Okanagan
Agricultural viability in the southern Okanagan Valley
is greatly influenced by the availability of irrigation water. The
researchers project that crop water demands and irrigation requirements will
increase by more than 35% from historic values by the latter part of the
present century. While the main lake and channel are expected to contain
enough water to meet these rising demands, agricultural operations dependent
on tributary flow will likely experience water shortages.
To deal with future water supply-demand mismatches, Neilsen et al.
advocate increased use of water conservation measures, such as
micro-irrigation and applying soil mulches. They also suggested that new
techniques, including regulated deficit irrigation and partial root zone
drying, would yield substantial water savings.
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While there
remain considerable uncertainties regarding the nature of future climate
changes at the regional and local scales, there is no question that the level
of CO2 in the atmosphere will continue to increase for several decades.
Enhanced atmospheric CO2 concentrations have generally been found to increase
crop production. This is
because
higher CO2 levels tend to improve plant water-use efficiency and rates of
photosynthesis. However, the
relationship is not simple. For instance, certain types of plants, such as
legumes, are expected to benefit more in the future than others, and the
nutritional quality of some crops will likely decline. In addition, there are
several factors, including moisture conditions and the availability of soil
nutrients, that could limit or negate the benefits of CO2 fertilization on
plant growth. Although some impact studies do attempt to incorporate CO2 effects
into their modelling, many researchers feel that there
are too many uncertainties to effectively integrate the effects of increased
atmospheric CO2.
Another
complicating factor in projecting future trends in crop yields is the
interaction of climatic changes and enhanced CO2 concentrations with other
environmental stresses, such as ozone and UV-B radiation. For example, warmer
temperatures tend to increase ground-level ozone concentrations, which, in
turn, negatively affect crop production. Studies
have suggested that the detrimental effects of enhanced ozone concentrations on
crop yields may offset any gains in productivity that result from increased
atmospheric CO2 levels.
Changing
winter conditions would also significantly impact crop productivity and growth.
Climate models project that future warming will be greatest during the winter
months. With warmer winters, the risk of damage to tree fruit and grape
rootstocks will
decline substantially in areas such as the southern Okanagan Valley.
However, warmer winters are also
expected to create problems for agriculture, especially with respect to pests, because
extreme winter cold is often critical for controlling populations. Warmer
winters may also affect the resilience of crops (see
Box 3).
Many crops
may be more sensitive to changes in the frequency of extreme temperatures than to
changes in mean conditions. For example, an extreme hot spell at the critical
stage of crop development has been shown to decrease the final yields of annual
seed crops and damage
tree fruit such as apples. Crops that require several years to establish (e.g.,
fruit trees) are especially sensitive to extreme events. To date, however, most
impact studies have focused on changes in mean conditions, with scenarios of extreme
climate events only now being developed.
Many experts believe that an increase in the frequency and
intensity of extreme events would be the greatest challenge facing the
agricultural industry
as a result of climate change.
Another
factor not usually included in modelling of climate change impacts is future
changes in wind patterns, mainly because wind projections from GCMs are highly
uncertain(21) and wind phenomena, in general, are poorly understood. However, wind is
clearly an important control on agricultural production, which strongly
influences evapotranspiration and soil erosion, especially on the Prairies. As such, exclusion of future wind dynamics increases
the uncertainty in assessments of climate change impacts.
