Climate Change and Agriculture Fact Sheet Series E3149 April 2011 FielD Crop Agriculture and Climate Change Julie E. Doll1 and Marci Baranski 1,2 1W.K. Kellogg Biological Station, Michigan State University, 2Michigan State University Extension How are greenhouse gases related to agriculture? Ultimately, the way we farm the land can directly affect Greenhouse gases such as carbon dioxide occur the amount of important greenhouse gases in the naturally in the atmosphere and keep the Earth warm, atmosphere. allowing us to survive on Earth. Over the last 200 years, the amount of greenhouse gases in the atmosphere In 2008, agriculture contributed about 7% of human- has increased as a result of burning fossil fuels and based greenhouse gas emissions in the United States3. other human activities1. The majority of scientists agree Much of this impact comes from the more potent that increased greenhouse gas levels are causing Earth’s greenhouse gases (see MSU Extension E3148): methane average global temperature to rise. Consequently, we largely from animal agriculture and nitrous oxide largely experience changes in climate at the local level (see from field crop agriculture. Agricultural soil management MSU Extension E3148). was responsible for 68% of total nitrous oxide emissions; these emissions are greatly influenced by the amount Field crop agriculture both emits and consumes of nitrogen fertilizer applied, the crop grown, and the weather patterns3. Figure 1 shows the relative greenhouse gases that affect climate – so agricultural contribution of major agricultural greenhouse gas management and policies can help combat climate change. sources in the United States. Two of the most important greenhouse gases are How will climate change affect Michigan field related to field crop agriculture: carbon dioxide (CO2) crop agriculture? and nitrous oxide (N2O). Field crop agricultural practices Global warming is likely to bring local shifts in both emit these gases and remove them from the temperature and in the amount and seasonal distribu- atmosphere. For example, through photosynthesis tion of precipitation. It is also likely to result in more crops remove carbon dioxide from the atmosphere and extreme weather such as droughts and periods of use it to build plant tissue. Some of this carbon can be heavy precipitation. Such changes can affect plant stored in the soil as soil organic matter. However, when growth, the spread of pests and diseases, and water soil is tilled, microbes are stimulated to more quickly availability in both positive and negative ways (Table 1). convert organic carbon to carbon Soil and fertilizer management dioxide, which escapes into the Ruminant livestock Agriculture as a portion of all atmosphere. In most (enteric fermentation) U.S. emissions 7% farmed soils, tillage Manure management has caused the release of 40–60% of original Rice cultivation soil carbon2. Soil microbes can also Field burning of crop residues emit nitrous oxide, especially when there 0 50 100 150 200 250 is excess nitrogen that Tg CO2 Eq. plants do not use. Figure 1: Relative contributions of agriculture to greenhouse gas emissions in 2008 (expressed in the unit CO2-equivalents). Total emissions increased by 16% from 1990–2008 from the U.S. agricultural sector. (Figure adapted from EPA 20103.) There are feedbacks so the issue is consequently Increased carbon dioxide concentrations in the complicated. For example, while greater rainfall and a atmosphere (carbon fertilization): Almost all plants longer growing season can enhance crop growth, they utilize one of two types of photosynthesis, C3 or C4. can also lead to more plant disease and different and The difference between these types is how the plant perhaps more virulent pests. Furthermore, if the greater uses carbon dioxide in the growth process. Michigan precipitation occurs in winter rather than summer, then C3 crops include soybeans and wheat while corn is a the longer growing season will not enhance rainfed C4 plant. In general, crop yields are enhanced by more yields and may delay springtime soil drying. If, on the carbon dioxide, with C3 plants responding more other hand, the greater precipitation occurs in summer strongly than C4 plants, so long as other factors such but in more intense storms, the benefit may be offset as water availability are not limiting their growth5. by nitrogen loss, erosion, and other fertility problems. However, estimates of increased yield from elevated carbon dioxide may be overestimated as most of these For now, the takeaway message is uncertainty. The experiments have been conducted in enclosures that climate is changing, and changes are likely to happen fail to represent field conditions and do not account for more rapidly in the future. We do not know exactly interacting factors such as weeds, nutrients, soil water, how climate change will affect Michigan field crops, and decreased air quality5,6. but we know there will be change, and the better we are prepared for it the more we can use it to our Warmer temperatures: The general warming trend of benefit. Agriculture’s ability to be nimble in adapting, as the Midwestern United States could allow varieties of well as having good information about changes and crops typically planted in more southern climates to be adaptive measures is key4. Below we discuss how planted further north7,8. While warmer temperatures documented and predicted changes in climate have can increase crop productivity1, there is an optimum the potential to affect field crop agriculture. See MSU temperature for reproductive growth. Once this Extension E3152 and E3153 for a detailed description of maximum is exceeded, plant and seed growth is crop adaptation and soil management in response to diminished. This can reduce yields9. Water availability changes in climate. also can become more limited as higher temperatures increase plant water use. More precipitation: While more rainfall during the Table 1: Representation of positive and negative growing season could benefit plants, the likely increases impacts of climate change on field crop agriculture in winter and spring precipitation, heavy downpours, Good or Bad and summer evaporation can lead to more times of Good Bad 8 for Ag? floods and water deficits . These predicted changes in precipitation and subsequent excesses or deficits of Increased CO2 concentrations water in the Midwest would negatively affect field crop agriculture7,8. Warmer temperatures Greater weather variability: Though winters may Greater weather variability be shorter due to warming temperatures, weather variability can pose an obstacle to some field crops. Crops more vulnerable Unpredictable occurrences like the spring freeze in to pests 2007 or extensive water logging of fields by excessive 7 Longer growing season rainfall could become more common, harming crops . Crops more vulnerable to pests: Plant pathogens are More precipitation highly responsive to increased rainfall. Similarly, insect abundance increases with temperatures9. Invasive weeds, insects, and pathogens from warmer climates may colonize northern soils, creating new, major pest problems for field crop farmers7. Much more research 1) Mitigation: intervention to reduce the is needed to understand changes in production due sources or enhance the sinks of to climate-induced shifts in diseases and weed and greenhouse gases1. insect pests5. 2) Sequestration: the removal of carbon dioxide from the atmosphere and Longer growing season: The Upper Midwest stands subsequent storage in carbon sinks to benefit from a longer growing season associated (such as oceans, forests, or soils) through with warmer temperatures7. longer growing seasons physical or biological processes, most provide more management flexibility, reduce the risk notably through photosynthesis10. of early frost, and allow longer-season varieties to 3) Adaptation: Initiatives and measures to be planted. reduce the vulnerability of natural and human systems against actual or What can agriculture do about climate change? expected climate change effects1. Although agriculture contributes to excess greenhouse gases in the atmosphere, it is possible to reduce emissions and even remove carbon dioxide from the atmosphere through specific land management practices. There are three main concepts central to interactions between climate change and agriculture: Table 2: Mitigation and sequestration strategies for field crop agriculture11,12 Goal Practice Additional benefit to farmers Reduce fossil fuel Renewable energy sources, Saves money, potential new consumption improved efficiency biofuel crops and markets. equipment, biofuel crop substitution Restore Crop diversity through Improves soil and water quality. (sequester) soil cover crops and rotations; Reduces erosion. carbon: increase increase crop residue carbon inputs quantity in no-till; manure to soil and compost additions Restore Permanent no-till, retain Improves soil, water, and air (sequester) soil crop residue, perennial crops quality. Reduces soil erosion carbon: reduce and fuel use. carbon loss from soil Reduce Better manage nitrogen Improves water quality. Saves nitrous oxide fertilizer use expenses, time, and labor. emissions Photos courtesy of KBS lTER - MSU Table 2 indicates some of the many specific strategies 8U.S. Global Change Research Program (2009). Regional Climate Impacts: related to agriculture. For example, research in Michigan Midwest. http://www.globalchange.gov/publications/reports/scientific- assessments/us-impacts/regional-climate-change-impacts/midwest