U.S. Wine Harvest Could Get Squashed by Warming, Study Says

Richard A. Lovett
for National Geographic News
July 11, 2006
Wine production in the United States could take a drastic hit if global
warming continues unabated, a new study says.

The grapes needed for premium wines are more sensitive to weather conditions than those used for table wine or grape juice.

If human-caused carbon dioxide emissions continue to rise, average temperatures in wine-producing regions will increase, the study says, as will the number of extremely hot days.

And a hotter, more variable climate will harm wine-grape ripening.

"We project a greater than 80 percent reduction in total premium wine production in the U.S.," said Noah Diffenbaugh of Purdue University in West Lafayette, Indiana.

Diffenbaugh co-authored the study, which appears today in the journal Proceedings of the National Academy of Sciences.

According to his team's data, warming could lead to a "more than a 50 percent [acreage] reduction in areas suitable for the highest-quality, most expensive wines."

Hot Grapes

In premium grapes, photosynthesis breaks down at temperatures above 95°F (35°C). Flavor ripening can fail with prolonged exposure to temperatures above 86°F (30°C).

Diffenbaugh's team found that as carbon dioxide gases increase, average growing-season temperatures might rise by about 5°F (3°C) by the year 2100.

Although that's a fairly significant change, an average of warmer days isn't by itself catastrophic for grape-growers, Diffenbaugh said.

The scientists also found that California's Napa and Sonoma wine regions, which currently see fewer than 14 superhot days each year, will see 55 or 60 of them by late in this century (California map, facts, more).

That's enough to completely knock out premium wine production in these regions, Diffenbaugh said.

Diffenbaugh's team used a climate model that was detailed enough to show changes on a 2.4-mile (4-kilometer) grid.

This allowed them to pick out small niches where wine grapes might still thrive in a warmer world.

The study also took into account the fact that warmer temperatures will open up two regions that Diffenbaugh considers to be presently unsuitable for premium wine growing.

"That's the coastal Pacific Northwest and the Northeast from upstate New York through Maine," Diffenbaugh said.

He adds that these regions' high humidity and frequent rains can undercut their grape-growing suitability because of fungus, rot, and mildew.

Chris Field, director of the Carnegie Institution's department of global ecology in Stanford, California, says that the new study represents an important advance in our understanding of global warming.

"This approach begins to give a much sharper picture of the kinds of things that can occur locally—the short-timescale events that can be very important for crops," he said.

Overall, he says, it's an additional reason to be concerned about climate change (see the current and future effects of global warming in National Geographic magazine).

"The picture they come out with is that the stresses are greater when you take these types of things into account.

"You can read [this study] as saying that the more we understand [about climate shift] the more serious the trends look. As we get a more sharply focused picture, we see additional stresses on lifestyles and economic systems."

Engineering Pinot Noir?

In California, late-season heat waves caused substantial wine-grape losses in 2003 and 2004.

But interest in the warming scare faded when 2005 produced better weather, says Dave Smart, of the department of viticulture (grape cultivation) and enology (study of wine-making) at the University of California, Davis.

"The wine-grape industry is not at all prepared for the consequences of climate warming," Smart wrote in an email to National Geographic News.

One method of mitigating heat damage, he says, is by installing overhead sprinkler systems in vineyards.

"However, the extent to which this strategy can be applied … may be extremely limited as we enter an era of increasing scarcity of water." (Related news: "UN Highlights World Water Crisis" [June 2003].)

In parts of Europe, he added, wineries are attempting a long-term policy of buying land in isolated regions where climate models indicate the weather will still be ideal for growing high-quality wine.

This suggests that the European wine community has "embraced that climate change is real and will have consequences to wine-grape production," Smart said.

Diffenbaugh notes that his study looked merely at climate and not at the things that wine producers might be able to do to cope.

He suggests, though, that wine makers may be able to create new grape varieties that would be more tolerant to heat, possibly by genetic engineering.

In the U.S. Midwest, he says, corn and soybean producers don't see global warming as a critical barrier to production.

"The people who do genetic engineering are pretty confident that given, say, ten years warning, they could engineer varieties of corn and soybeans that would be tolerant to whatever is coming."

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