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Global Warming Could Disrupt Agriculture Around The Globe

Chuck Woods (352) 392-1773 x 281

Hartwell Allen (352) 392-8194
Ken Boote (352) 392-1811

GAINESVILLE—University of Florida researchers are peeking into the next century at what might happen to food crops if global warming continues at its current rate, and what they found is a good news/bad news situation.

In the short run, the research shows, some crops thrive in warmer temperatures caused By increases in carbon dioxide and other greenhouse gases. But the picture could worsen later in the century if temperatures climb and rainfall patterns change around the globe.

One glimmer of hope: new genetically engineered plants that produce high yields in a changing environment.

“Carbon dioxide is the key to plant growth, and rising levels of the gas may be a silver lining for agriculture for a few decades,” says Hartwell Allen, crop and climate research scientist with the UF’s Institute of Food and Agricultural Sciences.

“Our research shows that increases in carbon dioxide do have some positive effects on the growth of most plants,” he said. “However, too much carbon dioxide will heat the atmosphere and disrupt agriculture around the globe as we know it.

“The warming changes will come very gradually over many decades. We’re certainly not going to start growing citrus in Georgia or winter vegetables in Minnesota anytime soon, if ever.”

The research project, funded By the U.S. Department of Agriculture, the Department of Energy and the Environmental Protection Agency, began in 1981 on soybeans and has been expanded to other crops during the last 10 years.

To find out how peanuts, rice, soybeans, sugar cane and forage crops react to elevated carbon dioxide, temperature, humidity and soil moisture levels, UF researchers are using computer-controlled greenhouses and growth chambers to simulate climate and environmental changes that may begin unfolding early in the next century.

In testing various “what if” scenarios for Florida agriculture, Allen and UF agronomist Ken Boote found that changes in temperature and rainfall could be the most troublesome. While slightly elevated temperatures did not affect the growth of most crops tested, global warming could cause rainfall to drop in some parts of the world and increase in others.

“We’re convinced the biggest problem could be changes in rainfall patterns and the availability of water,” Allen said.

He said soybean yields increased By 32 percent when carbon dioxide was doubled in the growth chamber. Increased carbon dioxide also boosted growth of citrus seedlings and rice. Sugar cane, corn and sorghum are not as responsive because they concentrate carbon dioxide in their cells.

Allen said crops such as rice and soybeans, for example, continue to grow under higher temperatures, but their ability to flower, pollinate and produce viable, high-quality seed is adversely affected. Under very high temperatures, plants reach a critical point or threshold beyond which photosynthesis and vegetative growth crash.

Increased carbon dioxide levels caused tomatoes to accumulate starch in their cells, making them yellow and thick.

But there may be room for adaptation. Boote said shifts in management practices and further improvements in genetic engineering will lead to crops that thrive in a warmer world.

“Researchers have already developed a few crops such as cotton and cowpeas that are more tolerant to heat and drought. In the future, we may need to transfer genes from plants growing in very hot desert environments to crops grown here in Florida and the Southeast,” Boote said.

With 1997 going down in the record books as the warmest year ever, there’s almost no question in the scientific community that rising carbon dioxide levels are beginning to warm the planet, Allen said.

“Just like a closed greenhouse traps heat from the sun, greenhouse gases — mostly carbon dioxide, but also methane, nitrous oxide, ozone and chlorofluorocarbons — trap heat that would otherwise escape,” he said. “Without this process, the earth would freeze. However, rising levels of these greenhouse gases will cause global warming and change our climate.

“We have very accurate measurements on increases in the level of carbon dioxide and other gases in the atmosphere, but our ability to predict global or regional climate changes is still in the developmental stage,” Allen said.

He said carbon dioxide levels in the atmosphere have risen about 30 percent since the 19th century. Air bubbles trapped in prehistoric ice in Antarctica and Greenland give researchers an accurate record of ancient climates. Since 1958, the concentration of carbon dioxide in the atmosphere has increased from 315 parts per million (ppm) to 365 ppm, and the rate of increase is accelerating.

If nothing is done, some predict carbon dioxide levels could double to 700 ppm within the next 100 years, he said. A similar doubling is projected for methane, a natural gas which is scarcer than carbon dioxide but more potent as a greenhouse gas.

“Some computer projections indicate greenhouse gases could cause average temperatures to rise By about 3 to 8 degrees Fahrenheit and change rainfall patterns around the globe,” Allen said. “Other models predict polar ice caps will melt and cause coastal flooding. Warmer weather may cause stronger storms, habitat changes for wildlife, and more weed, insect and disease problems.

“With world population growth, deforestation and a steady increase in the burning of fossil fuels, the global warming train has already left the station. In the coming century, the best we can hope for is to stabilize the world climate, perhaps at a somewhat warmer level, but one that will not cause great ecological changes around the planet,” Allen said.