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.”