Bordeaux wine in St. Émilion in southwestern France. (Georges Gobet/AFP/Getty Images)

Some in the upper echelons of government may still doubt human-caused climate change, but there are few such skeptics in the world’s vineyards. Wine growers around the world have been seeing the effects of a warming globe for years, while we were still debating it as a theoretical issue. Now that we are feeling the effects with increasing instances of severe weather, like frequent wildfires and stronger hurricanes, vignerons are facing existential questions about their future and the future of wine.

“Wine is a bellwether of climate change,” says Elizabeth Wolkovich, an associate professor of forest and conservation sciences at the University of British Columbia in Vancouver. “Much of the notion of terroir comes down to climate, so we are reshaping terroirs, with varied consequences.”

Climate change has made winners out of some cool regions that traditionally had trouble ripening grapes. Germany’s rieslings and the Loire Valley’s cabernet francs are enjoying more reliable harvests, year after year, than they were even a decade ago. English sparkling wine is challenging champagne. Sure, there are other factors involved, such as improved winemaking, but the effects of climate change are obvious.

There are negative effects, too. “I believe in climate change. I live it,” Gerhard Kracher told me. Kracher specializes in late-harvest and ice wines from Austria’s Burgenland region. We met last month in Bordeaux during Vinexpo, the biennial trade fair that focused, this year, on climate change.

“I used to be able to make an ice wine seven vintages every decade,” Kracher told me, referring to a dessert wine made from grapes picked while frozen on the vine. “Now, maybe three a decade.”

For Bordeaux, climate change’s effects are more subtle, but just as existential.

“Bordeaux is preparing for the future, but we are aware we need to act now,” Allan Sichel, head of the Bordeaux Wine Council, said during Vinexpo’s symposium on climate change. “Our objective is to preserve the characteristics of Bordeaux — freshness, elegance, balance, digestibility and aromatic complexity. To achieve that, we may need to change everything we do.”

At the very least, that means tinkering with the classic bordeaux blend of grape varieties. In descending order of their regional prominence, they are merlot, cabernet sauvignon, cabernet franc, petit verdot, malbec and carmenère.

For decades, merlot has been the backbone of great value bordeaux from $15 to $30, as well as the prestigious, pricier reds of St. Émilion and Pomerol. Merlot is the earliest to ripen, which was great when vintages were difficult but has become problematic. Warmer, shorter growing seasons risk higher sugars, and therefore alcohol, but lower development of aromas and flavors. Vintners are already responding by using more cabernet sauvignon and cabernet franc in their blends.

At Chateau Lagrange, in St. Julien, winemaker Matthieu Bordes has even ripped out some merlot vines and replanted with cabernet sauvignon. “I tend to go low on merlot in the blend, because it ripens unevenly,” with sugars climbing before favorable flavor characteristics develop, he told me during a tasting at Vinexpo.

With strong tannins and deep color, petit verdot used to be called “Dr. Wine” because it could heal a rough vintage. But it requires more work in the vineyard than other varieties and can dominate a wine if it becomes more than a small part of the blend. Today’s growers have learned to ripen it more reliably, and because it ripens later than merlot but sooner than the cabernets, it is gaining favor in some quarters. Plantings of petit verdot have nearly tripled, from 375 hectares (927 acres) in 2000 to 1,093 hectares (2,700 acres) last year.

“Petit verdot runs against the Bordeaux style of cabernet sauvignon or merlot, but if terroir includes weather patterns, then a change in style is part of the evolution,” says Vincent Bache-Gabrielsen, technical director of Chateau Belle-Vue in the Médoc region, which produces a 100-percent varietal wine from petit verdot.

Perhaps most shocking to traditionalists, Bordeaux’s response to climate change will challenge our very conception of the wine. Later this month, the growers of the Bordeaux-Bordeaux Superieur AOC, the council that sets the appellation’s rules, are expected to approve a list of 20 additional grape varieties that may be used in a wine labeled as bordeaux. The move, already approved by French national regulators and the legislature, will allow grapes such as marselan and touriga nacional to join the traditional blend. The varieties must have an advantage in terms of climate change or environmental protection (as in disease resistance, requiring fewer chemical treatments), explained Bernard Farges, president of the AOC.

“Climate change is challenging the very nature of our appellation system,” Farges said. “If our wine is defined by the blend of grapes, the style and typicity will change with the climate. Or is it defined by a style and flavors? If the latter, you need to change the blend to maintain the wine’s identity in changing circumstances.”

Around the world, wineries are responding to climate change by reducing their carbon footprint, practicing more environmentally friendly viticulture and planting different grape varieties. I plan to write about several of these initiatives, which will ultimately change wine as we know it in ways both subtle and dramatic.

“The underlying premise of all this is that the climate is changing, and you accept that you have to do something about it,” Farges said.

Dig Deeper: Environment + Food

Want to explore how a changing climate has impacted access to food? Check out our curated list of stories below.

Context matters: The impact of climate change on the wine industry

As severe weather situations like hurricanes and wildfires increase, the world’s vineyards are facing an existential crisis.

Get smart about the future of the world’s food supply

Offshore sea ranches that farm and harvest shellfish, finfish and seaweed have the potential to be a substitute for terrestrial farming.

Understanding how diet reforms can fight climate change

Earth’s population could swell to 10 billion by 2050. Making sure there’s enough food to go around — without destroying the environment — will require major changes to everyone’s diet.

More from Food:

Wine column archive