Anticipating more volatile weather, more extreme temperatures and violent storms in the future, scientists are busy analyzing the potential effects on agriculture.To help prepare for these potential changes, USDA recently completed a study and released a detailed report titled “Climate change and agriculture in the United States: Effects and adaptation.”

Based on their analysis, the authors say the effects will be variable but mostly detrimental to crop and livestock production, which contribute about $300 billion per year to the U.S. economy. Direct effects such as rising temperatures and altered precipitation will reduce crop productivity more than any potential benefit from higher carbon dioxide levels, according to the report, and indirect effects such as changes in the competitive ability of weeds, diseases, insect pests and beneficial insects also will challenge productivity.

For livestock specifically, the report lists four ways in which climate change could affect productivity.

  • Feed-grain production, availability and price: Each crop species has a given set of temperature thresholds that define the upper and lower boundaries for growth and reproduction, along with optimum temperatures for each developmental phase. Pollination, the authors note, is one of the most sensitive stages to temperatures, and exposure to high temperatures during this period can greatly reduce crop yields and increase the risk of total crop failure.
  • Pastures and forage crop production and quality: Many perennial crops have a winter chilling requirement and yields will decline if the chilling requirement is not completely satisfied.  Also, mid-winter warming can lead to early bud-burst or bloom of some perennial plants, resulting in frost damage when cold winter temperatures return.
  • Animal health, growth and reproduction: For many species, deviations of core body temperature in excess of 2°C to 3°C cause disruptions of performance, production, and fertility, the report notes. For cattle that breed during spring and summer, exposure to high temperatures decreases conception rates. Livestock and dairy production may be more affected by changes in the number of days of extreme heat than by adjustments of average temperature.
  • Disease and pest distributions: Warmer, more humid conditions will also have indirect effects on animal health and productivity through promotion of insect growth and spread of diseases. These effects are not well understood, but earlier springs and warmer winters could enable greater proliferation and survivability of pathogens and parasites. Regional warming and changes of rainfall distribution may lead to changes in distributions of diseases sensitive to temperature and moisture, such as anthrax, blackleg and hemorrhagic septicemia.

The report projects the U.S. agricultural system can largely adjust to climate change in the short term by expanding irrigated acreage, shifting regional crop preferences, rotating crops and changing management practices such as choice and timing of inputs and cultivation practices.

In the long term, however, the vulnerability of agriculture will depend on human responses according to the report. This will require “development of geographically specific, agri­culturally relevant, climate projections for the near and medium term; effective adaptation planning and assessment strategies; and soil, crop and livestock management practices that enhance agricultural pro­duction system resilience to climatic variability and extremes.” We’ll also need research and development in new crop varieties that are resistant to drought, disease and heat stress.

The full report (193 pages) is available online from the USDA.