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Impacts on Agriculture
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
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.
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.
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