"Climate change will impact agriculture by causing damage and gain at scales ranging from individual plants or animals to global trade networks." ⁽¹⁰⁾

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.,⁽¹¹⁾ who suggested that yields of canola, corn and wheat in Alberta would increase by between 21 and 124%.
• Singh et al.,⁽¹²⁾ 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.,⁽¹³⁾ 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 (e.g., reference 12). 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,⁽¹⁴⁾ thereby increasing general confidence in model projections.

Figure 1: Potential impacts of climate change on agricultural crops in Canada larger image [JPEG, 116.3 kb, 800 X 725, notice]

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.

BOX 1: Will the Prairies become drier? ^{(15, 16)}

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 (16) 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.(15) 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.

BOX 2: Water supply and demand in the Okanagan ⁽¹⁷⁾

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.(17) 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.

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.⁽¹²⁾

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.⁽¹⁸⁾

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.⁽¹⁷⁾ 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).

BOX 3: Would warmer winters benefit crops? ⁽¹⁹⁾

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 (e.g., reference 20) and damage tree fruit such as apples.⁽¹⁷⁾ 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.

Another important consideration for crop production is the observation that recent warming has been asymmetric, with night-time minimums increasing more rapidly than daytime maximums. Climate models project that this trend will continue in the future. This type of asymmetric warming tends to reduce crop water loss from evapotranspiration and improve water use efficiency.⁽²²⁾ Under such conditions, climate change impacts on crop productivity may be less severe than the impacts predicted assuming equal day and night warming.⁽²³⁾

Impacts on Livestock

There are more than 90,000 livestock operations in Canada, which accounted for more than $17 billion in farm cash receipts in 2000.⁽⁴⁾ Despite the economic importance of livestock operations to Canada, relatively few studies have examined how they could be impacted by climate change.

Temperature is generally considered to be the most important bioclimatic factor for livestock.⁽²⁴⁾ Warmer temperatures are expected to present both benefits and challenges to livestock operations. Benefits would be particularly evident during winter, when warmer weather lowers feed requirements, increases survival of the young, and reduces energy costs.⁽²⁵⁾ Challenges would increase during the summer, however, when heat waves can kill animals. For example, large numbers of chicken deaths are commonly reported in the United States during heat waves.^{(26, 27)} Heat stress also adversely affects milk production, meat quality and dairy cow reproduction.⁽²⁴⁾ In addition, warmer summer temperatures have been shown to suppress appetites in livestock and hence reduce weight gain. ⁽²⁸⁾ For example, a study conducted in Appalachia found that a 5°C increase in mean summer temperature caused a 10% decrease in cow/calf and dairy operations.⁽²⁸⁾

Provided there is adequate moisture, warmer temperatures and elevated CO2 concentrations are generally expected to increase growth rates in grasslands and pastures.^{(29, 30, 31)} It is estimated that a doubling of atmospheric CO2 would increase grassland productivity by an average of 17%,⁽²⁹⁾ with greater increases projected for colder regions⁽³²⁾ and moisture-limited grassland systems.⁽²⁹⁾ However, study results tend to vary greatly with location, and changes in species composition may affect the actual impacts on livestock grazing.⁽²⁹⁾ For instance, studies have noted future climate changes, particularly extreme events, may promote the invasion of alien species into grasslands,⁽³³⁾ which could reduce the nutritional quality of the grass.

An increase in severe moisture deficits due to drought may require producers to reduce their stock of grazing cattle to preserve their land, as exemplified by the drought of 2001 when many Prairie producers had to cull their herds. For the 2002 season, it was predicted that many pastures would be unable to support any grazing, while others would be reduced to 20-30% of normal herd capacity.⁽³⁴⁾

There is relatively little literature available on the impacts of extreme climate events on livestock. Nevertheless, storms, blizzards and droughts are an important concern for livestock operations.⁽²⁸⁾ In addition to the direct effects on animals, storms may result in power outages that can devastate farms that are heavily dependent upon electricity for daily operations. This was exemplified by the 1998 ice storm in eastern Ontario and southern Quebec, when the lack of power left many dairy farms unable to use their milking machines. This threatened the health of the cows (due to potential mastitis) and caused significant revenue losses.⁽³⁵⁾ Milk revenue was also lost through the inability to store the milk at the proper temperature. Furthermore, the lack of electricity made it difficult to provide adequate barn ventilation and heating, thereby making the animals more susceptible to illness.⁽³⁵⁾

Soil Degradation

"Soil degradation emerges as one of the major challenges for global agriculture. It is induced via erosion, chemical depletion, water saturation, and solute accumulation." ⁽¹⁰⁾

Climate change may impact agricultural soil quality through changes in soil carbon content, nutrient leaching and runoff. For example, changes in atmospheric CO2 concentrations, shifts in vegetation and changes in drying/rewetting cycles would all affect soil carbon, and therefore soil quality and productivity.^{(36, 37)}

Soil erosion threatens agricultural productivity and sustainability, and adversely affects air and water quality.⁽³⁸⁾ There are several ways that soil erosion could increase in the future due to climate change. Wind and water erosion of agricultural soils are strongly tied to extreme climatic events, such as drought and flooding, which are commonly projected to increase as a result of climate change.^{(21, 39)} Land use change could exacerbate these impacts, as conversion of natural vegetation cover cropland greatly increases the sensitivity of the landscape to erosion from drought and other climatic fluctuations.⁽⁴⁰⁾ Warmer winters may result in a decrease in protective snow cover, which would increase the exposure of soils to wind erosion, whereas an increase in the frequency of freeze-thaw cycles would enhance the breakdown of soil particles.⁽⁴¹⁾ The risk of soil erosion would also increase if producers respond to drought conditions through increased use of tillage summerfallow.

Pests and Weeds

Weeds, insects and diseases are all sensitive to temperature and moisture,⁽⁴²⁾ and some organisms are also receptive to atmospheric CO2 concentrations.^{(43, 44)} Therefore, understanding how climate change will affect pests, pathogens and weeds is a critically important component of impact assessments of climate change on agriculture.

Most studies of climate change impacts on weeds, insects and diseases state a range of possible outcomes, and have been generally based on expert opinion rather than results of field- or lab-based research experiments. Conclusions from these studies include the following:

• Elevated CO2 concentration may increase weed growth.⁽⁴²⁾
• Livestock pests and pathogens may migrate north as the frost line shifts northward.⁽²⁸⁾
• The probability of year-to-year virus survival may increase.⁽⁴⁵⁾
• Warmer winters may increase the range and severity of insect and disease infestations.⁽⁴²⁾
• Longer and warmer summers may cause more frequent outbreaks of pests, such as the Colarado potato beetle.⁽⁴⁶⁾
• Pathogen development rate and host resistance may change.⁽⁴⁷⁾
• Geographic distribution of plant diseases may change.⁽⁴⁸⁾
• Competitive interactions between weeds and crops may be affected.⁽⁴⁹⁾

Studies are needed to test and validate these predictions, and the results must be better incorporated into impact assessments.⁽⁵⁰⁾

Significant work has been completed on the climatic controls on grasshopper populations in Alberta and Saskatchewan.⁽⁵¹⁾ This research has shown that grasshopper reproduction and survival are enhanced by warm and dry conditions. For example, warm and dry weather in 2001 was associated with a 50% increase in the average number of adult grasshoppers per square metre, compared to values in 2000. Above-average temperatures increase the development and maturation of grasshoppers, and allow them to lay more eggs before the onset of frost. Mild winters also benefit grasshopper populations because extreme cold temperatures can kill overwintering eggs.⁽⁵¹⁾ An increase in temperature and drought conditions in the Prairies, as projected by climate models,⁽⁵²⁾ could lead to more intense and widespread grasshopper infestations in the future.

Recent work indicates that the relationships between elevated atmospheric CO2 concentrations, warmer temperatures and pest species are complex. An example is a study of the impacts on aphids,⁽⁴³⁾ serious pests that stunt plant growth and deform leaves, flowers and buds. Although elevated CO2 concentrations enhanced aphid reproduction rates, they also made the aphids more vulnerable to natural enemies by decreasing the amount of an alarm pheromone. This suggests that aphids may in fact become less successful in an enhanced CO2 environment.⁽⁴³⁾

Invasive species, such as weeds, are extremely adaptable to a changing climate, as illustrated by their large latitudinal ranges at present. Invasive species also tend to have rapid dispersal characteristics, which allow them to shift ranges quickly in response to changing climates. As a result, these species could become more dominant in many areas under changing climate conditions.⁽⁴⁴⁾

It is also expected that climate change would decrease pesticide efficacy, which would necessitate changes to disease forecasting models and disease management strategies.^{(48, 49)} This could involve heavier and more frequent applications, with potential threats to non-target organisms and increased water pollution,⁽⁴⁹⁾ as well as increased costs associated with pesticide use.⁽⁵³⁾ Similar trends are predicted for herbicide use and costs in the future.⁽⁵⁴⁾

Economic Impacts

Assessing the economic impacts of climate change on agriculture generally involves the use of a variety of tools, including climate, crop and economic models. Each step in the modelling process requires that assumptions be made, with the result that final outputs are limited by cascading uncertainties.⁽²⁵⁾ It is therefore not surprising that agricultural economic impact assessments in Canada are characterized by great variability.⁽⁵⁵⁾ On a general level, however, the economic impacts of climate change are expected to mirror the biophysical impacts (e.g., economic benefits are predicted where effects on crop yields are positive). Studies suggest that Canadian agriculture should generally benefit from modest warming.⁽²⁸⁾

It must be noted, however, that most economic impact assessments do not consider changes in the frequency and severity of extreme events. The sensitivity of agriculture to extreme events, as noted previously, suggests that overall economic losses could be more severe than commonly projected. For instance, the 1988 drought caused an estimated $4 billion in export losses,⁽⁵⁶⁾ and the 2001 drought is expected to result in record payouts from crop insurance programs of $1.1 to 1.4 billion.⁽⁶⁾ Economic impact studies also tend to aggregate large regions, and generally do not acknowledge the impacts on specific farm types and communities.⁽⁵⁵⁾

International markets will also play a significant role in determining the economic impacts of climate change on the Canadian agricultural sector. In fact, changes in other countries could have as much influence on Canadian agriculture as domestic changes in production.⁽⁹⁾ North American agriculture plays a significant role in world food production and, since Canada is generally expected to fare better than many other countries with respect to the impacts of climate change, international markets may favour the Canadian economy. Trade agreements, such as NAFTA and GATT, are also likely to affect Canadian agriculture;⁽⁵⁷⁾ however, quantitative studies of these issues are generally lacking.