The researchers also looked at how much land could be available to growers who adapt to warmer conditions, such as by planting heat-tolerant vines or altering their cultivation practices.

The study found that suitable acreage in Napa and Santa Barbara counties could actually be increased if growers are able to produce quality grapes that can tolerate up to 45 very hot days and average temperatures of 71 F (22 C) in the growing season. However, varieties currently grown in those conditions tend to produce considerably lower wine quality and value, the authors noted.

Winegrowers, with their knowledge of which cultivation techniques are most appropriate in a given climate, could benefit from the study's forecasts of temperature conditions, Diffenbaugh said.

"Climate change over the next few decades is of particular relevance for the wine industry," he said. "It's a big investment to put plants in the ground. They're slow to mature, and once they mature they're productive for a long time."

Some decisions growers make now could affect their vineyards in 30 years, he added, whether they consider the potential effects of local climate change or not. Moving a vineyard to a cooler location or planting different varietals could be costly for winegrowers, the study said. But in areas where less drastic temperature change is likely, growers may be able to maintain the quality of their grapes by using existing cultivation and winemaking techniques, Diffenbaugh said. Possible strategies include special trellis systems that shade vines, using irrigation to cool plants and adjusting fermentation processes in the winery.

"It's risky for a grower to make decisions that consider climate change, because those decisions could be expensive and the climate may not change exactly as we expect," Diffenbaugh said. "But there's also risk in decisions that ignore global warming, because we're finding that there are likely to be significant localized changes in the near term."

Diffenbaugh's coauthors are Michael White of Utah State University, Gregory Jones of Southern Oregon University and Moetasim Ashfaq of Oak Ridge National Laboratory, a former postdoctoral researcher at Stanford.

The study was supported in part by a National Science Foundation CAREER award to Noah Diffenbaugh.