Redrawing the Map of California’s Premier Wine Region

The vineyards at Chimney Rock Winery in Napa, Calif., Wednesday, Nov. 19, 2025. (Jessica Christian/San Francisco Chronicle via AP)

It was Labor Day 2017, and the remote thermometer at McIntyre Estate Vineyard in Monterey County’s Santa Lucia Highlands was registering a noontime temperature Steve McIntyre couldn’t quite believe: 104 degrees.

McIntyre jumped in his car, hoping the sensor was broken. Twenty miles later he stepped out into the searing air at his vineyard and knew there was no mistake. It would hit 116 before the day was over, the hottest since he first planted the site in 1973.

“It felt like a gut punch,” he said.

The U.S. is the largest wine-producing country outside Europe, and 80% of that output comes from California. For an industry in which even subtle shifts in temperature or humidity can transform a harvest’s value, increasing extremes and unpredictability pose an existential threat.

Extreme heat can kill a vine just as it can a human. As temperatures rise, so does the speed at which vines pull water from the soil. Once a plant starts losing water faster than it can rehydrate, it mounts a perilous last-ditch effort to save itself. 07-23-26

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