Grape growers may relocate
Posted on Monday, July 17, 2006
URL: http://www.nwanews.com/bcdr/News/37375/
SACRAMENTO, Calif. — The hotter days and warmer nights that global warming may bring could compel most premium wine grape growers to lower their quality or move to cooler sites by century’s end, say scientists who developed a new climate model of the United States.
This has huge implications for California’s wine-producing industry, which has grown to $ 17 billion in retail sales, according to the Wine Institute, a trade group in San Francisco.
Premium wine grapes are usually defined as such because they are used to make wine that sells for $ 7 or more per bottle. Lower-quality grapes end up in jug or fortified wine, as table grapes and as raisins.
Growing premium wine grapes requires the right climate: hot during the day and cool at night. Temperature extremes can ruin otherwise good wine grapes and were the focus of a study published in Monday’s edition of the Proceedings of the National Academy of Sciences.
Using a finely detailed model of the nation’s climate, scientists created daily temperature maps for the end of the century. These temperatures were then used to determine the “ Winkler region” for the wine, an industry gauge of the quality of a winemaking climate that considers total heat accumulation over a year.
Based on an increase in number of days on which the temperature exceeds 95 degrees, the researchers found an 81 percent decrease in the acreage suited to growing premium wine grapes.
“ We’re talking about anywhere between 40 to 60 more days” annually above 95 degrees in those areas, says Noah Diffenbaugh, climate scientist at Purdue University in Indiana and one of the study’s authors. “ You’re really talking about a new heat regime in these areas. ”
Some level of climate change is nothing new to wine-growing regions, said Greg Jones, climate scientist at Southern Oregon University and another study author. “ The growing season in Napa is 85 days longer now than in the 1930 s and 1940 s. ”
Lengthening the growing season is a good thing for wine grapes, because the best spend a long time slowly maturing on the vine, says Eric Aafedt, winemaker at Bogle Vineyards in Clarksburg. This gives the grapes enough time to develop the correct balance of flavor and sugar.
But when temperatures get too high, about 95 to 100 degrees, the grapes “ pretty much shut down, ” says Leon Sobon, of Shenandoah Vineyards in Amador County. “ If you get to about 100 degrees, the vine shuts down, and if you get to 100 day after day, the leaves start burning. ”
The study was a forecast of temperatures in the United States at the end of this century, but like all forecasts, it comes with a degree of uncertainty. What the climate scientists are certain about, however, is that the earth is warming.
The National Academy of Sciences recently released a report confirming that the earth is warming by one degree over the past century, and at an increased rate over the past 20 years.
“ There’s abundant evidence that we’re getting warmer, ” said Michael Hanemann, director of the California Climate Change Center at UC Berkeley, and a member of Gov. Arnold Schwarzenegger’s Climate Action Team. “ The question is, how will this trend continue, and that’s where the (climate ) models come in. ”
Hanemann also notes that many economic theories assume that changes in temperatures have a “ symmetric” relationship to agricultural output, meaning that if the weather is hotter or cooler, the crop yield decreases equally. But the yield of many crops, such as wine grapes, has a temperature threshold, or tipping point, beyond which “ the decline is like falling off a cliff. ”
Inez Fung, director of the Berkeley Atmospheric Science Center, said people may have doubts about the accuracy of climate predictions. She compares global warming to smoking cigarettes: Doctors know that smoking cigarettes is bad for your health and increases your risk of getting lung cancer. Climate scientists likewise know that global warming is happening and that carbon dioxide helps drive it.