Global Warming could slash US wine industry- a study reveals

Global warming could have devastating effects for many premium vineyards in California and across the nation by the end of the century, according to a new computerized climate projection released Monday.

The study released yesterday in Proceedings of the National Academy of Sciences revealed that areas suitable for growing premium wine grapes could be reduced by 50 percent, and possibly as much as 81 percent, due to the predicted rise in the number of days hotter than 95 degrees during the growing season, by the end of this century.

The major problem: an increase in the frequency of extremely hot days, said Noah Diffenbaugh of the Department of Earth and Atmospheric Sciences at Purdue University.

Grapes used in premium wines need a consistent climate. When temperatures top nearly 95 degrees, the vines have problems maintaining photosynthesis and the sugars in the grapes can break down, said Diffenbaugh, a co-author of the report.

An international team of scientists concluded in the journal Proceedings that increasing weather problem for grapes in such areas as California's Napa and Sonoma valleys.

Marginal vineyards countrywide might be eliminated and those capable of producing the most expensive premium wines may be reduced by half, the researchers revealed.

Although wine is produced in 48 states, California's $ 16.5-billion industry, with more than 500,000 acres of vineyards, accounts for almost 90% of the country's wine grapes.

"We found that at elevated greenhouse gas concentrations, the frequency of extremely hot days increases to the point where it is impossible to grow premium wine grapes in many areas of the country," said Noah Diffenbaugh.

"Certainly, the Napa Valley, the Sonoma Valley and the Santa Barbara area all exhibit enormous losses of production in the future climate," Diffenbaugh added.

Until now, climate studies focused only on the impact of average temperature increases on wine production and concluded that wine growers might, if anything, benefit from the temperature increases expected in coming decades.

The recent study, funded by the National Science Foundation, the National Aeronautics and Space Administration and Purdue University, involved five months of supercomputer estimations. It is the pioneer study in which researchers have been able to calculate the daily temperature swings from various climate-change scenarios in such detail.

For the purposes of their computer simulation, the scientists assumed that levels of carbon dioxide and other gases would continue to rise to more than twice their present level by 2100, as marked in standard global-warming scenarios.

Eventually, the computer simulation indicated that the number of extremely hot days during the growing and ripening season would increase by three to eight weeks in much of the South Central and Southwestern United States, which is too hot to produce premium wine grapes.

The number of cool days would also decrease by more than three weeks in many regions of the nation, opening up some areas for new grape production, but also multiplying the possibility of more rot, mildew and fungus infections in those areas.

On average, the growing season would begin 22 days earlier around the country. The West Coast would experience one of the biggest changes, resulting in a considerable alteration to the quality of its grape harvest.

Suitable grape-growing areas in California would shrink to a narrow coastal band, the researchers said, while premium wine-grape areas would shift into the Pacific Northwest and New England. In the Southwest and the Midwest, wine production would be almost completely eliminated.

"This is a call to arms," said Karen Ross, president of the California Assn. of Winegrape Growers, which represents 1,000 growers in the state. "We need to pay attention now. We ought to start thinking about what can be done now to impact the severity of what might happen," concerned with the problem, Ross said