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.
Jones, and now Vierra, are convinced the climate shifts occurring in inland Mendocino County to the north deviate sharply from Sonoma and Napa.
Jones' study, for example, found that the number of hot summer days over 95 degrees in the Ukiah Valley has steadily declined over five decades while temperatures in Napa have risen.
In the 1950s, Ukiah posted an average of 51 days where the high temperature reached 95 degrees or more, according to Jones' study. The average for the last 10 years is just 29 days.
The shift is so dramatic that for three summers in a row Ukiah has on average posted cooler temperatures than Napa.
"If we didn't have the supporting data, no one would believe it," said Vierra.
Charlie Barra isn't surprised. A Redwood Valley grape grower for 60 years, Barra knows from experience that conditions have changed.
"I know it's cooler at night because my own vineyards are cooler," said Barra, who has more than 100 acres of grapes.
Last summer, a seminar at Gloria Ferrer Winery in the Carneros district focused on global warming and the wine industry. It touched not only on how winemakers can reduce their carbon footprints but also on how climate change can affect premier grape-growing regions. Some winemakers said they had witnessed local changes, such as more heat spikes and fewer spring frosts, and those changes were influencing the way they manage vineyards.