Global warming could wither many premium U.S. vineyards by the end of the century, according to a new computerized climate projection released Monday.

A predicted rise in the number of days in the growing season hotter than 95 degrees, due to rising levels of greenhouses gases, could sharply reduce the areas suitable for vintage wine-grape production, an international team of scientists concluded in research published in the Proceedings of the National Academy of Sciences.

Marginal vineyards nationwide might be eliminated and those capable of producing the most expensive premium wines may be reduced by half, the researchers reported. 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 percent of the nation’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, a member of the research team who studies the impact of climate change at Purdue University.

“Certainly, the Napa Valley, the Sonoma Valley, and the Santa Barbara area all exhibit enormous losses of production in the future climate,” Diffenbaugh said. “The Willamette Valley in eastern Oregon takes a big hit.”

Several wine industry experts not connected with the new study initially were skeptical of the new climate projection and its dire prediction.

“If their definition of an extreme hot day is 95 degrees, I’d tell them that they don’t know squat about grapes,” said James T. Lapsley, an expert at the University of California, Davis on the economics of wine and the history of California wine.

If temperatures do rise high enough, however, “Ultimately we will have to be looking for other places to grow grapes,” Lapsley said. But “what these guys are saying is a little more stark.”

Gladys Horiuchi, a spokesperson for the Wine Institute in San Francisco, said, “It raises a lot more questions than it answers. Our group would want to take time to investigate some of the assertions in the paper.”