Higher temperatures could hurt California and other premium winegrowing regions of the United States in the next 30 years, according to a new study led by Stanford University climate scientists.

Writing in the June 30 edition of Environmental Research Letters, the scientists report that by 2040, the amount of land suitable for cultivating premium wine grapes in high-value areas of Northern California could shrink by 50 percent because of global warming. However, some cooler parts of Oregon and Washington state could see an increase in premium grape-growing acreage due to warming, according to the study.

These results follow the researchers' 2006 climate study, which projected that as much as 81 percent of premium wine grape acreage in the country could become unsuitable for some varietals by the end of the century.

"Our new study looks at climate change during the next 30 years – a timeframe over which people are actually considering the costs and benefits of making decisions on the ground," said Noah Diffenbaugh, an assistant professor of environmental Earth system science and a center fellow at the Woods Institute for the Environment at Stanford. Diffenbaugh co-authored both studies. 

Climate change, from global to local

Most American wine comes from the West Coast. California alone produces on average more than 5 million gallons per year, accounting for about 90 percent of the nation's total wine production, according to the Wine Institute, a trade organization representing California winemakers. The institute estimated the retail value of the state's wine industry in 2010 at $18.5 billion.

The new study focused on premium wines – the 25 percent most expensive wines on the market – and how global warming could affect growing conditions in four premium wine-producing counties by 2040: 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.

But that could change, and soon.

"There will likely be significant localized temperature changes over the next three decades," Diffenbaugh said. "One of our motivations for the study was to identify the potential impact of those changes, and also to identify the opportunities for growers to take action and adapt."