Grapegrowers Feeling the Heat
Short heat spikes, likely a result of global warming, could cause long-term changes to how and where wine grapes are grown
On July 28, Williams Selyem winemaker Bob Cabral walked along a row of Pinot Noir vines in the famed Allen Vineyard in Sonoma's Russian River Valley. "Take a look at these," he said, cupping his hand around a bunch. The fruit looked more like burnt, half-cooked popcorn kernels than grapes.
That's what five days of 100 degree-plus weather can do to premium wine grapes. And the heat wave that hit California this July was not an isolated incident. In 2005, Australia's Clare Valley saw a weeklong heat spike that pushed up grape sugars faster than producers could harvest. And this year, New Zealand's Central Otago region, which as the world's southernmost wine region is normally quite cool, experienced a fruit-scorching, four-day heat spike in which the temperature reached 104 degrees.
In fact, events such as these may have been just a taste of things to come for winemakers everywhere. According to a study released in July, if global warming continues at its current pace, extreme weather events such as heat spikes could shrink the total area suitable for growing premium wine grapes in the United States by as much as 81 percent by the end of this century. Europe and Australia, the report suggests, could be similarly affected.
 | |
| Study suggests that the total potential grapegrowing area of the U.S. may decline as much as 81 percent over the next century. | |
Purdue University professor Noah Diffenbaugh, coauthor of the study, which was published and presented at the Proceedings of the National Academy of Sciences, said that until now, most studies on global warming have looked at long-term rises in temperature. While these studies have raised concerns about winegrowing's future, this one brings a new sense of urgency. Based on the researchers' calculations, with the current projected increase in the number of heat spikes, over the next 100 years U.S. wine production would become most favorable only in coastal Oregon, Washington and the northeast.
For vintners in cooler regions such as these, however, climate change is viewed as much as a blessing as a curse. "It's obvious that the overall climate in Germany is different than it was 10 years ago," said Nik Weis, winemaker at St.-Urbans-Hof in the Mosel. "Since 1991, which was the last weaker vintage, we didn't have a single one that could be considered as bad. Every vintage was good." However, he has concerns, citing the extreme heat of summer 2003, which resulted in some water-stressed vines, sunburned grapes and dried-out berries. "To my knowledge, this never occurred in the past."
Even rainy, cool England has seen an increase in wine quality. "Our summers are much drier now here," said Paul Woodrow-Hill, vineyard manager of sparkling-wine producer Nyetimber Vineyard. "This allows grapes to be picked at ideal ripeness levels." And that's gotten the attention of some outsiders. "It is true that there has been some interest from Champagne houses in purchasing land in England," said Woodrow-Hill. Champagne producer Didier Pierson, who said he saw the potential of the area because his wife is English, has bought land in Kent, in the south.
While cooler regions are more attractive now, traditionally warmer regions are hurting from the heat spikes. Spanish producer Miguel Torres Sr. declared at a global warming symposium in Barcelona that he was going to have to take his Catalan grape plots further and further north.
And some believe heat isn't the only thing to worry about. In Australia's Clare Valley, Wakefield chief winemaker Adam Eggins said, "We just had the coldest winter in 25 years. So it's not just heat spikes, it's cold spikes. The extremes will become extremer."
So should Australian growers be planting new land along the southern coast and in Tasmania? Will all American winegrowing eventually shift to New England and the Pacific Northwest? That depends, said Diffenbaugh.
"Those areas that become advantageous from a temperature perspective are likely to have pretty serious problems from excess moisture, both from humidity and serious precipitation," he said. So abandoning Napa vineyards today for greener pastures further north isn't necessarily the answer.
Instead, much could be done to respond to the changes in seasonal conditions, claims Diffenbaugh. For example, he said, "People are trying to breed heat-tolerant [vines]."
Growers and vintners in California, New Zealand and Australia said they are reconsidering their approach in the vineyard. In the past 15 years, they have opened up the leaf canopy over the grapes to allow more sunlight in to better ripen the grapes. "That is going to be moderated now," said Napa grower Andy Beckstoffer. Concerned about overexposure when he planted a new vineyard in Rutherford four years ago, Beckstoffer made sure the rows ran in a direction that limited direct sunlight.
Many Californians are also maintaining a cover crop between rows of vines, to keep heat from reflecting off the ground. But cover crops won't work for everyone, said Grant Taylor, owner of Valli in Central Otago, where many vineyards are very gravelly. "I'm not sure how you put a cover crop on them since they're rocks, not soil."
Eggins is laying straw in Wakefield's vineyards to retain moisture and help slow the ripening, but he's also taking preventive measures in the winery, increasing capacity in case a heat spike forces him to pick several vineyards in a short time span. "If your winery's good for 5,000 tons over three months, you better build a 10,000-ton winery," he said. "The flavor ripening curve is still going to happen, it's just going to happen faster."
Perhaps. Diffenbaugh points out that his study's conclusions were based on the assumption that the environment behaves as it has up to now, and that greenhouse gas concentrations continue to build at their projected rate. A lot can happen over the next century. "We're pointing to the environmental variables that will be of greatest concern going forward," Diffenbaugh said. "The question is, really, what will be done on the ground?"
