Climate change will affect agriculture over the next 30 to 50 years and will require scientists and farmers to develop new systems to adapt to more variable weather patterns.

Jerry Hatfield, Laboratory Director and USDA-ARS Supervisory Plant Physiologist at Ames, Iowa, said more extremes in weather, including drought, heat and excessive rainfall, will increase production risk.

Hatfield discussed the challenges of climate change during the recent Texas Plant Protection Association annual conference in College Station.  He said change is real but left it to others to determine if those changes come from natural cycles, human activity or a combination. The need to prepare for change, however, offers challenges for the entire agricultural industry.

He said variability in temperature and precipitation has affected agriculture since the early 1900s. In some cases, higher temperatures have increased yields. “But that also increased variability,” he said. Cotton and corn yields have increased significantly over the past century. A big part of the increase results from better cotton varieties and transgenics and improved corn hybrids.

“Corn yields stabilized in the 1960s,” Hatfield said, “but has been variable the last 20 years because of precipitation and temperature variability.”

He said temperature changes may not occur uniformly. “The assumption (with the trend showing warmer temperatures every year) is that every place is warmer,” he said. “But some areas cooled and some areas warmed. Alaska witnessed the biggest warming trend from 1901 through 2006.”

He said in the future the earth likely will see more days in which the temperature exceeds 90 degrees. “South Texas, for instance, may see even more, possibly half the year with temperatures above 90 degrees.

“We will have to develop agricultural systems to deal with higher temperatures.”

Precipitation

Precipitation will change, as well.  He said the United States as a whole experiences extremely variable rates of precipitation. “Since 1901 some areas have gotten drier and some have become wetter.” The Southwest falls into the drier category, as does the Southeast.

Hatfield said seasonal changes have also occurred. Winters in the Southern United States are drier. “Those seasonal differences will become more extreme,” Hatfield said. “We have to get used to dry periods and we are likely to experience longer periods of drought interspersed with longer periods of wet. We expect less of a happy medium. That will be a challenge for agriculture.”

Hatfield said changes in the earth’s atmosphere, including higher levels of carbon dioxide and other noxious gases, affect temperatures and humidity. “The United States is becoming more humid,” he said.

Also, nighttime temperatures are increasing. He said the mean temperature changes are mostly the result of higher nighttime temperatures. Those higher night temperatures have a significant effect on plant growth, he said. “Higher temperatures at night mean a higher rate of respiration. We’re asking a plant to work 24 hours a day. That hastens senescence and reduces yield potential.”

Plant physiology

He said an “overlooked piece of the puzzle is the physiological aspect of climate change.” Changes affect a plant’s growth rate, water use, and heat stress. “Increasing variability in precipitation will change water availability on both extremes (wet and dry).”

He said rainfall and extreme temperatures at the beginning and the end of a growing season and during critical growth periods, such as pollination, may keep crops from reaching yield potential. Higher temperatures decrease the growing season. “Plants move through growth stages more quickly,” Hatfield said. “Increased nighttime temperatures have a significant impact on vegetative growth and plant reproduction. Yields are affected because of the shorter reproductive period.”

He said crops will have less time for grain fill and seed size will be smaller.

Pest management will also change.

“Weeds love carbon dioxide and show a positive response to carbon dioxide concentrations. An increase of carbon dioxide levels from 380 parts per million to 720 parts per million may result in a 100 percent increase in weed populations. Weeds are much more responsive to carbon dioxide than crop species.”

Hatfield said the changes could encourage herbicide resistance. “It may take more herbicide to kill weeds.”

He said insect and disease pressure also may increase with “a more favorable environment over the winter and more humid conditions during the growing season.”

Additional stress, he said, also makes plants more susceptible to environmental injury.

Quality also suffers in climate change scenarios. Hatfield said higher temperatures may affect protein content in wheat, aflatoxin levels in corn and could reduce quality in wine, raisins and other crops.

“Climate change will affect agriculture,” Hatfield said, and will increase production risk. “But agriculture will adapt to in-season variability and uncertainty. Agriculture has always adapted.”