Agriculture and Food Supply Impacts & Adaptation

Climate Impacts on Agriculture

Increased carbon dioxide levels may accelerate the growth of some crops. Source: USDA (2009)

Agriculture is an important sector of the U.S. economy. In addition to providing us with much of our food, the crops, livestock, and seafood that are grown, raised, and caught in the United States contribute at least $200 billion to the economy each year. ^[1]

Agriculture and fisheries are highly dependent on specific climate conditions. Trying to understand the overall effect of climate change on our food supply can be difficult. Increases in temperature and carbon dioxide (CO₂) can be beneficial for some crops in some places. But to realize these benefits, nutrient levels, soil moisture, water availability, and other conditions must also be met. Changes in the frequency and severity of droughts and floods could pose challenges for farmers and ranchers. Meanwhile, warmer water temperatures are likely to cause the habitat ranges of many fish and shellfish species to shift, which could disrupt ecosystems. Overall, climate change could make it more difficult to grow crops, raise animals, and catch fish in the same ways and same places as we have done in the past. The effects of climate change also need to be considered along with other evolving factors that affect agricultural production, such as changes in farming practices and technology.

Impacts on Crops

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Despite technological improvements that increase corn yields, extreme weather events have caused significant yield reductions in some years. Source: USGCRP (2009)

Crops grown in the United States are critical for the food supply here and around the world. U.S. exports supply more than 30% of all wheat, corn, and rice on the global market. ^[2] Changes in temperature, amount of carbon dioxide (CO₂), and the frequency and intensity of extreme weather could have significant impacts on crop yields.

Warmer temperatures may make many crops grow more quickly, but warmer temperatures could also reduce yields. Crops tend to grow faster in warmer conditions. However, for some crops (such as grains), faster growth reduces the amount of time that seeds have to grow and mature. ^[1] This can reduce yields (i.e., the amount of crop produced from a given amount of land).

For any particular crop, the effect of increased temperature will depend on the crop's optimal temperature for growth and reproduction. ^[1] In some areas, warming may benefit the types of crops that are typically planted there. However, if warming exceeds a crop's optimum temperature, yields can decline.

• Higher CO₂ levels can increase yields. The yields for some crops, like wheat and soybeans, could increase by 30% or more under a doubling of CO₂ concentrations. The yields for other crops, such as corn, exhibit a much smaller response (less than 10% increase). ^[3] However, some factors may counteract these potential increases in yield. For example, if temperature exceeds a crop's optimal level or if sufficient water and nutrients are not available, yield increases may be reduced or reversed.
• More extreme temperature and precipitation can prevent crops from growing. Extreme events, especially floods and droughts, can harm crops and reduce yields. For example, in 2008, the Mississippi River flooded just before the harvest period for many crops, causing an estimated loss of $8 billion for farmers. ^[1]
• Dealing with drought could become a challenge in areas where summer temperatures are projected to increase and precipitation is projected to decrease. As water supplies are reduced, it may be more difficult to meet water demands.
• Many weeds, pests and fungi thrive under warmer temperatures, wetter climates, and increased CO₂ levels. Currently, farmers spend more than $11 billion per year to fight weeds in the United States. ^[1] The ranges of weeds and pests are likely to expand northward. This would cause new problems for farmers' crops previously unexposed to these species. Moreover, increased use of pesticides and fungicides may negatively affect human health. ^[1]

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Impacts on Livestock

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Beef cattle and pasture/rangeland distribution in the continental United States. Source: USGCRP (2009)

Americans consume more than 37 million tons of meat annually. ^[2] The U.S. livestock industry produced $100 billion worth of goods in 2002. ^[4] Changes in climate could affect animals both directly and indirectly.

• Heat waves, which are projected to increase under climate change, could directly threaten livestock. A number of states have each reported losses of more than 5,000 animals from just one heat wave. ^[1] Heat stress affects animals both directly and indirectly. Over time, heat stress can increase vulnerability to disease, reduce fertility, and reduce milk production.
• Drought may threaten pasture and feed supplies. Drought reduces the amount of quality forage available to grazing livestock. Some areas could experience longer, more intense droughts, resulting from higher summer temperatures and reduced precipitation. For animals that rely on grain, changes in crop production due to drought could also become a problem.
• Climate change may increase the prevalence of parasites and diseases that affect livestock.The earlier onset of spring and warmer winters could allow some parasites and pathogens to survive more easily. In areas with increased rainfall, moisture-reliant pathogens could thrive. ^[3]
• Increases in carbon dioxide (CO₂) may increase the productivity of pastures, but may also decrease their quality. Increases in atmospheric CO₂ can increase the productivity of plants on which livestock feed. However, studies indicate that the quality of some of the forage found in pasturelands decreases with higher CO₂. As a result, cattle would need to eat more to get the same nutritional benefits.

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Impacts on Fisheries

American fisheries catch or harvest five million metric tons of fish and shellfish each year. ^[2] These fisheries contribute more than $1.4 billion to the economy annually (as of 2007). ^[5] Many fisheries already face multiple stresses, including overfishing and water pollution. Climate change may worsen these stresses. In particular, temperature changes could lead to significant impacts.

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The ranges of marine species have shifted northward as waters have warmed.
Source: USGCRP (2009)

• The ranges of many fish and shellfish species may change. Many marine species have certain temperature ranges at which they can survive. For example, cod in the North Atlantic require water temperatures below 54°F. Even sea-bottom temperatures above 47°F can reduce their ability to reproduce and for young cod to survive. In this century, temperatures in the region will likely exceed both thresholds. ^[1]
• Many aquatic species can find colder areas of streams and lakes or move northward along the coast or in the ocean. However, moving into new areas may put these species into competition with other species over food and other resources, as explained on the Ecosystems Impacts page.
• Some diseases that affect aquatic life may become more prevalent in warm water. For example, in southern New England, lobster catches have declined dramatically. A temperature-sensitive bacterial shell disease likely caused the large die-off events that led to the decline. ^[1]
• Changes in temperature and seasons could affect the timing of reproduction and migration. Many steps within an aquatic animal's lifecycle are controlled by temperature and the changing of the seasons. For example, in the Northwest warmer water temperatures may affect the lifecycle of salmon and increase the likelihood of disease. Combined with other climate impacts, these effects are projected to lead to large declines in salmon populations. ^{[6] [7] [8]}

In addition to warming, the world's oceans are gradually becoming more acidic due to increases in atmospheric carbon dioxide (CO₂). Increasing acidity could harm shellfish by weakening their shells, which are created from calcium and are vulnerable to increasing acidity. ^[1] Acidification may also threaten the structures of sensitive ecosystems upon which some fish and shellfish rely. ^[3]

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International Impacts

Internationally, the effects of climate change on agriculture and food supply are likely to be similar to those seen in the United States. However, other stressors such as population growth may magnify their effects. For example, in developing countries, adaptation options like changes in crop-management or ranching practices or improvements to irrigation are more limited than in the United States and other industrialized nations.

To learn more about adaptation options, visit the Agricultural and Food Supply Adaptation section.

Impacts to the global food supply concern the United States because they can affect food prices here at home. In addition, food shortages abroad can pose humanitarian crises and national security concerns.

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References

1. USGCRP (2009). Global Climate Change Impacts in the United States . Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

2. U.S. Census Bureau (2011). The 2011 Statistical Abstract: International Statistics .

3. CCSP (2008). The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Backlund, P., A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M. Ryan, S. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L Meyerson, B. Peterson, and R. Shaw. U.S. Environmental Protection Agency, Washington, DC, USA.

4. U.S. Bureau of Economic Analysis (2002). 2002 Benchmark Input-Output Data: Standard Make and Use Tables at Summary Level .

5. USDA (2007). 2007 Census of Agriculture: Volume 1, Chapter 1: U.S. National Level Data

6. CCSP (2008). Preliminary Review of Adaptation Options for Climate-Sensitive Ecosystems and Resources (PDF). A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Julius, S.H., J.M. West (eds.), J.S. Baron, B. Griffith, L.A. Joyce, P. Kareiva, B.D. Keller, M.A. Palmer, C.H. Peterson, and J.M. Scott (authors). U.S. Environmental Protection Agency, Washington, DC, USA.

7. CCSP (2008). Analyses of the effects of global change on human health and welfare and human systems . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Gamble, J.L. (eds.), K.L. Ebi, F.G. Sussman, T.J. Wilbanks, (authors). U.S. Environmental Protection Agency, Washington, DC, USA.

8. Field, C.B., L.D. Mortsch, M. Brklacich, D.L. Forbes, P. Kovacs, J.A. Patz, S.W. Running and M.J. Scott (2007). North America. In: Climate Change 2007: Impacts, Adaptation and Vulnerability . Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change Parry, M.L., O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson (eds.). Cambridge University Press, Cambridge, United Kingdom.

Adaptation Examples in Agriculture

Climate change will likely impact agricultural practices in the United States through more frequent water shortages, extreme weather events, flooding, and shifts in growing seasons. To learn more about how climate change can impact agriculture and food production, visit the Agriculture and Food Supply Impacts section.

Farmers and ranchers have always had to cope with variability in the weather. But climate change will likely produce more permanent shifts in temperature and precipitation. Climate change impacts on agriculture and food production will vary by region. In some places, warmer temperatures may extend the growing season, while in other regions more heavy downpours may increase crop losses. Regardless of whether shifts in climate are ultimately beneficial or harmful, the agricultural industry will have to modify certain practices to adapt to new conditions as a result of anticipated changes in weather patterns. Specific adaptation approaches ^[1] include:

• Diversifying crops to adjust to changing temperature and precipitation patterns
• Adopting water and soil moisture conservation measures that minimize the impact of potential seasonal water shortages
• Changing livestock breeding practices and shifting grazing patterns
• Developing and using disease-resistant crop and livestock species ^[1]

The following case studies, examples, and related links are illustrative and not intended to be comprehensive.

Tools are being developed to make the food supply more resilient to climate change

Farming in Montana. Source: Montana Department of Environmental Quality (2011)

While strategies for responding to climate change will continue to develop over time, some options have been identified: ^[1]

• Aerial and satellite imagery can be used to monitor broad-scale patterns, such as changes in plant mortality and the spread of invasive plant species. Farmers can then use this information to make decisions about adjusting agricultural practices.
• Federal agencies can modify support and subsidy programs to encourage the planting of more diverse sets of crops or the adoption of innovative agricultural practices in areas where yields are threatened.
• Government agencies and the private sector can distribute and encourage the use of technologies to harvest rainwater, conserve soil moisture, and use water more efficiently. "Dryland farming" is a technique that uses soil moisture conservation and seed selection to optimize production under dry conditions. For more information about this practice, visit the adaptation section of the Great Plains Impacts & Adaptation page.
• Ranchers can reduce the loss of livestock during extreme heat events by improving ventilation in barns and increasing shade.
• Farmers and researchers can work to develop and breed crops that are more tolerant of droughts or to increased precipitation and flooding.
• Farmers can select crops that can best take advantage of increased levels of carbon dioxide in the atmosphere.
• With earlier springs and warmer winters increasing the risk of disease to crops and livestock, for example, by increasing the survival rate of parasites, farmers and ranchers can develop and use disease-resistant crop and livestock species. Also, to minimize the spread of disease among animals, ranchers can modify livestock breeding practices so that animals are living in less densely packed conditions, and move grazing herds to new areas.
• To combat potential increases in polluted agricultural runoff from heavier precipitation events, farmers can use buffers and modify or reduce fertilizer and pesticide application.

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USDA works to address climate change impacts on agriculture

The USDA Climate Change Program Office was created to address the climate change impacts on agriculture and food production. The details of USDA's overall adaptation plan to address climate change will continue to be refined over the next several years, and USDA has already sponsored several activities aimed at minimizing the risks of climate change to agricultural activity throughout the United States. For example:

• USDA Agricultural Research Services (ARS) is placing climate change impacts high on the list of priorities for upcoming research. Specifically, ARS will be researching how to build better models that simulate crops' responses to changes in weather and water and how to bolster the resilience of agricultural systems.
• The Risk Management Agency funds partnerships with states, universities, and other organizations to develop risk management tools to assist agricultural producers in minimizing risks, like those associated with climate change.
• In 2010, USDA released a report that analyzed the impacts of climate change on crop insurance. Although the report does not provide any definitive recommendations about crop insurance programs, it recognizes that past climate conditions may not fully represent future climate, which may require new modeling tools to be used as part of insurance programs.

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USDA works with farmers to improve water-use efficiency

The Environmental Quality Incentives Program (EQIP), run by USDA Natural Resources Conservation Service provides financial and technical support to agricultural producers. Several projects supported by EQIP employ water-use efficiency strategies to help farmers increase yields with less water. In 2010, 28 projects in nine states assisted agricultural professionals to shift practices to react to the projected change in resources. ^[2]

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References

1. NRC (2010). Adapting to the Impacts of Climate Change . National Research Council. The National Academies Press, Washington, DC, USA.

2. Interagency Climate Adaptation Task Force (2011). Federal Actions for a Climate Resilient Nation: Progress Report of the Interagency Climate Change Adaptation Task Force (PDF). U.S. White House, Washington, DC, USA.