Could the Napa Valley, the nation's best known wine region, be undone by global warming?

Calling the local industry the "canary in the coal mine," Napa wine business officials acknowledge its vulnerability if climate change produces significantly warmer weather from Carneros to Calistoga. The precise impact, though, is all but unknowable.

Premium wines depend on grapes whose character is formed by a delicate balance of temperatures, with rain occurring at the right times.

If global warming shakes things up, Napa vintners may have to juggle where grape varietals are planted, modify trellising and canopy practices and strive for breakthroughs in vine genetics, said Terry Hall, a spokesman for Napa Valley Vintners.

That's the optimistic scenario.

A bleaker picture was laid out in a study published last summer in the Proceedings of the National Academy of Sciences. The report warned that wine grape acreage in the United States could be reduced as much as 80 percent if the Earth heats up significantly.

This set off a media firestorm, Hall said. "With Napa at the top of the pyramid, all the headlines across the world said Napa is going to hell in a handbag."

Vintners don't deny that climate change or global warming is occurring, Hall said, but predicting the impact on the local wine industry is a "huge unknown."

If California heated up 1.7 degrees Centigrade (3 degrees Fahrenheit) over the next 50 years, as the study predicted, that raises more questions than it answers, according to Hall.

Would that change occur mostly in the winter, when vines are dormant, or would grapes be subjected to more scorching heat in the summer and fall?

As the Central Valley becomes hotter, it's possible that more ocean fog would be pulled into Napa, providing a cooling effect, Hall said. Two of the hottest years in world history, 1998 and 2005, were two of the coldest Napa Valley years, he said.

Chardonnay, a cool weather grape, would be most vulnerable if conditions become hotter. The issue isn't whether chardonnay vines would thrive in heat -- they would -- but whether the fruit would achieve the necessary sugar-acid balance for great wine.

Ninety percent of Napa Valley vineyards have been replaced since the early 1990s due to phylloxera, Hall noted. This demonstrated the industry's ability to overcome a threat with new plantings, he said.

At the end of the day, global warming isn't primarily a wine industry problem, but a world problem, Hall said. "There are bigger questions involved in this than, 'Are we going to be able to continue to grow great cabernet sauvignon?'"

Six months ago, the Napa Valley Vintners created a climate change task force to explore what the industry could do to be more energy efficient, thus lowering its production of carbon dioxide and other greenhouse gases.

Some vintners have made major steps in reducing the use of electricity in the winery and regular gasoline and diesel in vineyard cultivation.

Shafer Vineyards spent $1 million two years ago to install solar panels that generate enough energy to address all of the winery's electrical needs. State energy rebates cut the cost in half.

Robert Sinskey Vineyards installed a solar energy system that meets 75 percent of its need. To run its trucks and tractors, the winery takes restaurant food waste and brews its own biodiesel fuel, owner Robert Sinskey said.

"I feel business as a whole needs to ... take a leadership role to manage its (carbon) footprint," Sinskey said. Reducing the winery's greenhouse gas emissions "makes us feel better about being in business."

The prospect of climate change has always been in the back of his mind, which is why he chose 200 acres in the cooler Carneros region for his vineyard, he said.

Customers appreciate businesses that are environmentally friendly, said Sinskey, who has been farming organically since 1990. "It generates good will," he said.

Because they produce a prestige product, Napa vintners could serve as role models that inspire others to fight global warming, said Bob Massaro, a Napa contractor and advocate for "green" building practices.

If American industries and local governments take the lead, consumers can be inspired to do their part to cut energy use and live more sustainably, he said.

Moira Johnston-Block, an environmentalist who helped found Friends of the Napa River, said the Napa Valley wine industry has a special obligation to be on the forefront of enlightened energy practices.

The Napa Valley lifestyle depends on the success of the "magical grape," said Johnston-Block, who fears the worst if global warming isn't turned around.

"I don't want this to be Thompson seedless in 20 years. This is where we're heading," she said.

Mick Winter, who runs Web sites and publishes books about environmental issues, says some diversification in Napa County's ag focus might not be such a bad thing.

For a county with such a major focus on agriculture, Napa produces precious little actual food, Winter said. In the long run, wine is nice, but food is essential, he said.

And so the discussion goes. When thinking about a possible global apocalypse, there is much to focus the mind.

Whatever happens, be assured that the wine industry is paying attention, Hall said. Vintners will be a nimble as they need to be to adjust to changing conditions.

"We're not losing our industry anytime soon," he said.