California and Washington’s premium wine grape growing regions could shrivel by up to 50 percent by 2040, warn Stanford University scientists.

On the other hand, bad news for California could be good news for Oregon, as warmer temperatures actually expand the grape growing regions in some parts of the Northwest.

“Our new study looks at climate change during the next 30 years – a time frame over which people are actually considering the costs and benefits of making decisions on the ground,” said Noah Diffenbaugh, assistant professor of environmental Earth system science at Stanford, who co-authored the study, in a Stanford press release.

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“Climate change over the next few decades is of particular relevance for the wine industry,” Diffenbaugh said. “It’s a big investment to put plants in the ground. They’re slow to mature, and once they mature they’re productive for a long time.”

The research, published in Environmental Research Letters, looked specifically at the regions where the top 25 percent priciest wines are produced: Napa and Santa Barbara counties in California, Yamhill County in Oregon’s Willamette Valley and Walla Walla County in Washington’s Columbia Valley.

“We focused on these counties because their mild climates have made them major sources of high-quality grapes, and because they represent both cool and warm growing conditions,” Diffenbaugh said.

Both California and Washington’s wine industry stood to lose ground, but Oregon could actually see milder, wine-friendly temperatures in more areas.

For example, California’s Napa Valley, famous for pinot noir, cabernet, and other top tipples, has historically experienced growing seasons with an average temperature of less than 68 Fahrenheit (20 Celsius) and fewer than 30 days over 95 Fahrenheit.

But by 2040, the average temperature during the Napa Valley growing season could increase as much as 2 degrees Fahrenheit (1.1 Celsius), with the number of days over 95 Fahrenheit increasing by 10. That could reduce by half the amount of land historically hospitable for wine grapes.

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Threats to California’s wine industry are a threat to the world’s taste for cabernet sauvignon, chardonnay and other favorite California wines.

California produces on average more than 5 million gallons per year, or about 90 percent of the nation’s total wine production, according to the Wine Institute, a California winemakers trade organization.

Loss of wine revenues would be yet another hit to the economically troubled Golden State. The Wine Institute estimated the retail value of the state’s wine industry in 2010 at $18.5 billion.

To develop their forecasts of the West Coast’s changing climate the researchers used a model that assumed an increase of 1.8 degrees Fahrenheit (1 degree Celsius).

“World governments have said that to reduce the negative impacts of climate change, global warming should be limited to an increase of 1 degree Celsius,” Diffenbaugh said.

But even that modest increase in temperature, caused the wine barrels to run dry.

“I was surprised that local temperature changes could have such a big impact on an important industry with only 1 degree Celsius of global warming.” Diffenbaugh said.

Knowing that climate change could shrivel their harvests, winegrowers can plan ahead, but planting for the future can be a gamble.

“It’s risky for a grower to make decisions that consider climate change, because those decisions could be expensive and the climate may not change exactly as we expect,” Diffenbaugh said. “But there’s also risk in decisions that ignore global warming, because we’re finding that there are likely to be significant localized changes in the near term.”

“Humans are amazingly resilient, and individual growers will of course make decisions as they read the signs on the ground,” Diffenbaugh added.

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“We’re trying to understand how the climate that works so well for growing great wine grapes right now might be affected by even modest global warming,” Diffenbaugh said. “We can’t know the future before it happens, but if we don’t ask the question, we may be surprised when reality unfolds.”

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IMAGE 1: Wine grapes growing in California (Wikimedia Commons).

IMAGE 2: California’s wine growing regions (Wikimedia Commons).

IMAGE 3: Wine grapes growing in California (Wikimedia Commons).