July 10, 2006 -- Extreme weather events triggered by global warming threaten to eliminate more than 80 percent of the best U.S. wine-producing regions by the end of this century, according to a new study published today.
The report's conclusions -- which appear online in the Proceedings of the National Academy of Sciences -- could have multibillion-dollar implications for the U.S. wine industry.
"Where things are headed now, we're likely to see some very dramatic changes in sectors that are not only economically important, but culturally and aesthetically very valuable," said Noah Diffenbaugh, a co-author of the study and atmospheric scientist at Purdue University.
Wine sales in the United States -- including imports -- total an estimated $26 billion a year, according to the Wine Institute, a California wine industry group.
California sales are $16.5 billion a year, and the United States is the world's fourth-largest grape producer.
In the last 50 years, the study says, average temperatures have warmed by about 1.6 degrees Fahrenheit in the main wine-producing regions of California, Oregon and Washington.
Virtually all climate scientists blame the rise on human-caused greenhouse gases -- like carbon dioxide -- released into the atmosphere from the burning of fossil fuels.
Looking at the average temperature increase doesn't tell the whole story, researchers say.
"What really hits the winegrape plants hard is the frequency of extremely hot days," Diffenbaugh said.
Using high resolution computer models and historical observations, the team has for the first time attempted to predict how well grape plants will be able to tolerate "extreme temperature days" that reach at least 95 degrees Fahrenheit. The conclusions predict the outlook isn't good.
The most tolerant winegrape plants are able to handle 14 days of 95 degree-plus weather in a season before they were ruined by the heat.
The models predicted that the number of those hot days would increase to anywhere from 30 per to 60 per season.
"Our minimum increase is more than double the maximum tolerance," Diffenbaugh said. "It's just too hot for the wine grapes too many days of the year."
Check the Temperature
The study's results show that areas "marginally suitable" for producing wine in today's climate would be nearly eliminated, and that the areas currently producing the most expensive, highest-quality wine would decline by more than half.
Scientists predict that climate change may shift production of the best wines from places like Napa Valley to vineyards in the Pacific Northwest and New England -- locations traditionally considered too cool for production.
Heavy amounts of rainfall and humidity in those areas may create another problem.
"Those are not areas where, given a change in temperature, conditions are going to be hospitable," Diffenbaugh said. "What we would expect in those areas is serious problems with mildews, fungus and rots affecting the plants."
The report notes that wine grapes are excellent harbingers of climate change because attributes like acidity, alcohol content and flavor are so closely studied.
"It's perhaps the well-studied system because people have kept such good records and been so in tune with climate and changes in climate," Diffenbaugh said. "So it gives us increased confidence in our ability to project the relationships going forward."
While the report contains predictions for the future, some effects of climate change are already being seen in places like Spain.
There, warm temperatures are forcing growers to higher, cooler grounds in the Pyrenees mountains. Winemaking is just one of many agricultural industries that are dealing with climate change.
While some of the changes in climate can help crops, the adverse costs may outweigh the benefits, researchers have said.
The Intergovernmental Panel on Climate Change, an international group of hundreds of climate scientists, has said that "even though increased CO2 concentration can stimulate crop growth and yield, that benefit may not always overcome the adverse effects of excessive heat and drought."
"This certainly isn't good news," Diffenbaugh said. "It's a snapshot of where the climate space is headed, given where greenhouse gas emissions are now, and where they're pointed in the future."
However, Diffenbaugh pointed out that the study's predictions might not come true if something was done soon to reduce the amount of greenhouse gases getting pumped into the atmosphere.
"There's still a chance to curb those greenhouse gas emissions and stabilize them at lower levels than where we're pointed now," he said. "The decisions that we make now actually are in very large part determining where we end up in the future."