Noah Diffenbaugh, of Stanford's Department of Environmental Earth System Science, has plugged in present day temperature data, extrapolated climate projections and concluded that in the Napa Valley, the amount of land suitable for growing premium grapes could decrease by half.
"Napa produces such great wines because the temperatures are so favorable," Diffenbaugh said. "There are fewer than 30 hot days, where the temperature reaches 95 degrees Fahrenheit, during the average growing season, but, in the next 30 years, the number of hot days will increase."
According to Diffenbauch's study, the average temperature during the growing season could increase by as much as two degrees, Fahrenheit, with the number of hot days increasing by as many as 10. Those additional peaks could cause serious damage unless growers adapt to them. The study also shows temperatures will increase for wine growers in Santa Barbara County and as far north as Oregon.
"Areas like the Willamette Valley in Oregon could benefit," Diffenbaugh said.
Napa Valley growers and agricultural experts remain somewhat skeptical about the report.
"They are looking at too broad a set of data," Terry Hall of the Napa Valley Vintners Association said."In February, we released our own data study with help from Scripps Institution and Stanford University. It uses more specific data points. I think this new study is too big."
"The Napa Valley is unique," Matt Ashby, who grows grapes at Mondavi, said. "There are too many other factors. Some of the hottest summers, elsewhere, have been among the coolest here."