Dr. Michael Roberts, one of the lead authors of the study, said, “While crop yields depend on a variety of factors, extreme heat is the best predictor of yields.”

Temperatures higher than 85 degrees Fahrenheit for corn, 86 degrees for soy, and 89 degrees for cotton cause damage to crops, reducing yields.   By the end of this century, temperatures are predicted to rise by as much as 11 degrees Fahrenheit due to global warming, according to a recent US Global Change Research Program report (PDF format).

Risks of Inaction

Yield losses of up to 80% for corn, cotton and soy will clearly have devastating effects on American farmers. Additionally, these yield losses will be disastrous for US and global food security.  Though much of the focus has been on the costs and impacts of federal policy, this study shows that the cost of doing nothing and putting farmers and the world food supply at grave risk is the most critical calculation.

According to the study, “The United States produces 41% of the world’s corn and 38% of the world’s soybeans. These crops comprise two of the four largest sources of caloric energy produced and are thus critical for world food supply.”

For More Information

For more information on the Columbia University and North Carolina State University study, go here.

For more information on the effects of climate change on agriculture, go here.

The full report can be found here; the section on agricultural impacts can be found here. Key findings of the report include:

• Human-caused changes in US climate are already taking place and are expected to increase (p. 27)
• Climate change puts increasing stress on water resources (p. 41)
• Crop and livestock production will face greater challenges due to climate change (p. 71)
• Actions taken now to mitigate and adapt to changing climate can reduce future impacts (p. 11)

Agriculture and Climate Change

The report illustrates significant effects (and costs) from global warming on crops and livestock due to increased pests and weeds, water stress, diseases, and weather extremes such as longer dry periods and heavy downpours.

Agriculture and Water Resources

• NOAA expects climate change to make dry areas drier and wet areas wetter, putting added stress on agricultural and grazing systems across the country.
• Dry periods will be longer, making droughts more intense, and precipitation will be heavier, increasing risks of flooding.

Crop Production

• Though some crops (and especially weeds) respond positively to low increases in temperature and carbon dioxide concentration, the report explains that moderate to intense warming can harm crop growth and yield.
• Research shows that moderate warming decreases yields of crops grown in all regions of the U.S., including corn, wheat, sorghum, beans, rice, cotton and peanuts, and higher temperatures can affect crops’ ability to reproduce even in well-watered conditions.
• Increased temperatures and carbon dioxide concentrations also favor weeds and insect pests. Warming temperatures may result in the northern migration of invasive weeds which have been confined due to low winter temperatures.

Livestock Production

• Climate change will likely cause increased heat stress in livestock, which can make animals more susceptible to disease and parasites or kill them outright.
• Forage quality decreases with higher carbon dioxide concentrations, making it more difficult to feed livestock from pastures and rangelands.

Agricultural Climate Change Adaptation: Not cheap

The costs to agriculture of adapting to climate change are often ignored.  For example, weed suppression will increase costs for herbicides and more frequent spraying.  Currently, these costs vary across regions and are higher where it is hotter. New crop varieties can be designed for tolerance to drought and heat or a longer growing season, but developing these new varieties and making changes to farming operations to use them may be substantial.

Where development of new varieties is not possible, it maybe necessary to grow different types of crops entirely which means starting from scratch in terms of equipment, storage and infrastructure – a very expensive prospect.

For more information

• Report Home page:  Global Climate Change Impacts in the United States
  • Direct link to the report’s Agriculture chapter (PDF format)
• US Global Change Research Program web site