HOPLAND -- St. Helena winemaker George Vierra says wine snobs will find it "unfathomable" that climate changes may be transforming Mendocino County into a higher-quality grape-growing region than neighboring Sonoma County.
Or worse yet, the touted Napa Valley.
"Yet such a shift is supported by available data and expert analysis," said Vierra.
For Vierra it's a surprising development after 35 years of overseeing wine production for Napa Valley icons such as Charles Krug and Robert Mondavi wineries, and his own Vichon and Merlion labels.
"I was among the many who believed Mendocino vineyards were probably 'too hot' to produce quality grapes for high-end premium wines," Vierra said.
Yet, an expert analysis of 50 years of summer highs shows that the Ukiah Valley is now a cooler grape-growing region than Napa Valley.
The findings are attracting the scrutiny of winemakers such as Vierra and climate experts who specialize in weather-related effects on grape-growing regions.
Vierra's own quest to understand changes in Mendocino vineyards took root last year after he assisted in making a wine from organically grown pinot noir grapes in Hopland.
"I was amazed," said Vierra.
Vierra said he unexpectedly found acidic levels of the Hopland grapes comparable to those grown in the famously cool Carneros region at the southern tip of Napa and Sonoma counties. That's important because grape acidity falls significantly slower in cool regions, a process that can be sensed in the taste of a finished wine.
To better understand why, Vierra sought the opinion of nationally known climatologist Gregory Jones of Southern Oregon University. Jones the year before had compiled, analyzed and published findings from a study of 50 years of Wine Country temperature data.
Jones' findings substantiated a warming trend in Sonoma and Napa counties, which he said is already altering grape-growing conditions. Jones said a pattern of warmer overnight temperatures appears to be stewing some cool-loving varietals.