Climate change would likely cause the yields of several major California crops to decline significantly by 2050, while others would not change. Scientists at Lawrence Livermore National Laboratory (LLNL), UC Merced and others recently modeled the effect of climate change for six of California's most valuable perennial crops: wine grapes, almonds, table grapes, oranges, walnuts and avocados (Agricultural and Forest Meteorology 141 [2–4]: 208–18).

“In California, 20 to 30 years is the productive lifespan for most of these plants,” says David Lobell, who was agricultural ecologist at LLNL when he led the study. “If we can get a picture of how the climate will change during this interval, we can evaluate what that means in terms of projected crop yields.” In addition, keeping the time frame relatively short limits modeling uncertainty.

The projections showed variable results. Wine-grape yields, for instance, would change little over the next century, but the other crops exhibited moderate-to-substantial declines. The amount of uncertainty was considerable, but the overall trend was toward decreased yields.

“More than 95% of the simulations for almonds, table grapes, walnuts and avocados showed a negative response to warming by mid-century,” Lobell says. “The current climate is either at or above the optimum temperatures for the crops we studied, and all climate models project at least some warming during this period.”

Lobell is now senior research scholar at Stanford University. He and his colleagues have recently expanded their study to more crops in California; it will be released in coming months on the California Energy Commission Climate Action Team Web site.