Agriculture and Food Supply

Climate Factors | Implications for North America
Agriculture is highly sensitive to climate variability and weather extremes, such as droughts, floods and severe storms. The forces that shape our climate are also critical to farm productivity. Human activity has already changed atmospheric characteristics such as temperature, rainfall, levels of carbon dioxide (CO2) and ground level ozone. The scientific community expects such trends to continue. While food production may benefit from a warmer climate, the increased potential for droughts, floods and heat waves will pose challenges for farmers. Additionally, the enduring changes in climate, water supply and soil moisture could make it less feasible to continue crop production in certain regions.
The Intergovernmental Panel on Climate Change (IPCC, 2007) concluded:

Recent studies indicate that increased frequency of heat stress, droughts and floods negatively affect crop yields and livestock beyond the impacts of mean climate change, creating the possibility for surprises, with impacts that are larger, and occurring earlier, than predicted using changes in mean variables alone. This is especially the case for subsistence sectors at low latitudes. Climate variability and change also modify the risks of fires, pest and pathogen outbreak, negatively affecting food, fiber and forestry.

Climate Factors

Several factors directly connect climate change and agricultural productivity:

• Average temperature increase
• Change in rainfall amount and patterns
• Rising atmospheric concentrations of CO2
• Pollution levels such as tropospheric ozone
• Change in climatic variability and extreme events

Most agricultural impact studies have considered the effects of one or two aspects of climate change on a particular farming activity. Few, however, have considered the full set of anticipated shifts and their impact on agricultural production across the country.
Average temperature increase: An increase in average temperature can 1) lengthen the growing season in regions with a relatively cool spring and fall; 2) adversely affect crops in regions where summer heat already limits production; 3) increase soil evaporation rates, and 4) increase the chances of severe droughts.
Change in rainfall amount and patterns: Changes in rainfall can affect soil erosion rates and soil moisture, both of which are important for crop yields. The IPCC predicts that precipitation will increase in high latitudes, and decrease in most subtropical land regions—some by as much as about 20 percent. While regional precipitation will vary the number of extreme precipitation events is predicted to increase (IPCC, 2007).
Rising atmospheric concentrations of CO2: Increasing atmospheric CO2 levels, driven by emissions from human activities, can act as a fertilizer and enhance the growth of some crops such as wheat, rice and soybeans. CO2 can be one of a number of limiting factors that, when increased, can enhance crop growth. Other limiting factors include water and nutrient availability. While it is expected that CO2 fertilization will have a positive impact on some crops, other aspects of climate change (e.g., temperature and precipitation changes) may temper any beneficial CO2 fertilization effect (IPCC, 2007).
Pollution levels such as tropospheric ozone: Higher levels of ground level ozone limit the growth of crops. Since ozone levels in the lower atmosphere are shaped by both emissions and temperature, climate change will most likely increase ozone concentrations. Such changes may offset any beneficial yield effects that result from elevated CO2 levels.
Change in climatic variability and extreme events: Changes in the frequency and severity of heat waves, drought, floods and hurricanes, remain a key uncertainty in future climate change. Such changes are anticipated by global climate models, but regional changes and the potential affects on agriculture are more difficult to forecast.

Implications for North America

The IPCC concluded that, for North America as a whole (IPCC, 2007):

Moderate climate change will likely increase yields of North American rain fed agriculture, but with smaller increases and more spatial variability than in earlier estimates. Most studies project likely climate-related yield increases of 5-20 percent over the first decades of the century, with the overall positive effects of climate persisting through much or all of the 21st century.

• Food production is projected to benefit from a warmer climate, but there probably will be strong regional effects, with some areas in North America suffering significant loss of comparative advantage to other regions.
• The U.S. Great Plains/Canadian Prairies are expected to be particularly vulnerable.
• Crops that are currently near climate thresholds (e.g., wine grapes in California) are likely to suffer decreases in yields, quality, or both.
• Climate change is expected to improve growing conditions for some crops that are limited by length of growing season and temperature. (e.g. fruit production in the Great Lakes region and eastern Canada).

Agriculture in the U.S. and other industrialized countries is expected to be less vulnerable to climate change than agriculture in developing nations, especially in the tropics, where farmers may have a limited ability to adapt. In addition, the effects of climate change on U.S. and world agriculture will depend not only on changing climate conditions, but will also depend on the agricultural sector's ability to adapt through future changes in technology, changes in demand for food, and environmental conditions, such as water availability and soil quality. Management practices, the opportunity to switch management and crop selection from season to season, and technology can help the agricultural sector cope with and adapt to climatic variability and change.

The U.S. Global Change Research Program (USGCRP) has commissioned a federal study on the potential effects of climate change on agriculture. The USGCRP Synthesis and Assessment Product 4.3 will address the following questions:

• What factors influencing agriculture, land resources, water resources, and biodiversity in the United States are sensitive to climate and climate change?
• How could changes in climate exacerbate or ameliorate stresses on agriculture, land resources, water resources, and biodiversity?
• What are the indicators of these stresses?
• What current and potential observation systems could be used to monitor these indicators?
• Can observation systems detect changes in agriculture, land resources, water resources, and biodiversity that are caused by climate change, as opposed to being driven by other causal activities?

References

• IPCC, 2007: Climate Change 2007: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Parry, Martin L., Canziani, Osvaldo F., Palutikof, Jean P., van der Linden, Paul J., and Hanson, Clair E. (eds.)]. Cambridge University Press, Cambridge, United Kingdom, 1000 pp.