Global warming no friend of California wines: study

A worker carries a container while picking grapes at sunrise at a vineyard in Napa Valley, September 12, 2008.

SAN FRANCISCO (Reuters) - Global warming could make it more difficult for California's prized Napa Valley to make high quality wines over the next 30 years, but could improve grape-growing in Oregon, a study published on Thursday suggests.

A research team led by Stanford University scientists examined four premium wine-growing counties in the West.

Those were Santa Barbara County and the Napa Valley in California, Yamhill County in Oregon's Willamette Valley and Walla Walla County in Washington state's Columbia Valley.

The scientists, whose study appeared in the journal Environmental Research Letters, applied climate models and historical weather data to predict how global warming would affect those fertile regions.

They assumed a 23 percent increase in atmospheric greenhouse gases by 2040. That is a conservative scenario, amounting to a 1.8 degree Fahrenheit rise in average global temperature, said study co-author Noah Diffenbaugh, an assistant professor of earth sciences at Stanford University.

In northern California's Napa Valley, one of the world's best wine-making regions and a key contributor to the state's $18.5 billion wine industry, the results of climate change could be dramatic.

An uptick of 2 degrees Fahrenheit over 30 years could shift half the lands hospitable to pinot noir or cabernet sauvignon beyond the acceptable band of temperatures required for those high quality varieties, which is typically around 68 degrees, according to the study.

"We do see a shift in Napa," Diffenbaugh said. The hotter weather would reduce the quality of the grapes.

Hotter weather also was predicted to reduce suitable grape-growing acreage in California's Santa Barbara County and the Columbia Valley in Washington.

But warmer conditions would significantly increase opportunities for high-quality grape growing in the Willamette Valley in Oregon, where conditions at present are considered too cool for some premium wines, according to the study.

Still, the researchers' forecast is no guarantee the Willamette Valley will become the next Napa.

"A lot more than temperature goes into making wine," Diffenbaugh said. "But temperature is one consistent factor across the highest-quality wines."

A 2006 climate study projected that as much as 81 percent of premium wine grape acreage in the United States could become unsuitable for some varietals by the end of the century.

This latest study looks at effects of climate change on the wine industry over a shorter time frame, more in-line with what growers would use to make decisions, Diffenbaugh said.

(Editing by Alex Dobuzinskis and Greg McCune)