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.”