Rising temperatures could transform Wine Country's mild climate into one as sweltering as Tijuana, Mexico, eliminating Sonoma and Napa counties' competitive edge in producing world-class wines.
That's the conclusion of a study released Monday and published in the Proceedings of the National Academy of Sciences.
Areas in California suitable for growing premium wine grapes could be reduced by 50 percent -- and possibly as much as 81 percent -- by the end of this century because of global warming.
The study, the second report in two years on global warming's impact on premium wine, indicates increasing weather woes for wine grapes in California if fossil fuel consumption continues unabated.
In 2004, the Union of Concerned Scientists released a report warning that within 80 years most of Sonoma and Napa counties could become too hot to grow premium wine grapes. If so, it would severely affect an industry that contributes more than $5 billion to the regional economy, defines the Wine Country lifestyle and anchors more than 100,000 acres of vineyards.
While growers and winemakers are concerned about global warming, they don't believe rising temperatures would necessarily destroy the state's $45 billion wine industry. They said adjustments in vineyard management, irrigation practices and varietal selection could keep grapes the leading crop in the North Coast and in California.
Nick Frey, executive director of the Sonoma County Grape Growers Association, said the Pacific Ocean and its cooling maritime influence are the most critical factors in producing Sonoma County's premium-quality grapes. He said even if there are more hot days in the future, the Pacific Ocean will still be there to cool things down at night, creating the sugar-acid balance essential for fine wine.
"It's the cooling nighttime temperatures and fog from the Pacific Ocean that make Sonoma County such a great wine region," said Frey.
The primary change in the weather will be an increase in the frequency of extremely hot days, said Noah Diffenbaugh, a co-author of Monday's report and a scientist in the Department of Earth and Atmospheric Sciences at Purdue University.
Grapes used in premium wines need a consistent climate, he said.