Climate change has become the all-purpose culprit for seemingly every problem, from AIDS to zoonotic diseases. Just this week, Democrats in the House of Representatives floated a resolution declaring that climate change could lead to increased prostitution. Meanwhile, in California, the press is trumpeting new research predicting doom for the state’s legendary wine industry. “Study: California Can Kiss Its Vineyards Goodbye,” a San Jose Mercury News headline blared last month. Apparently, climate activists think that if they threaten everyone’s favorite pinot noir, we’ll all roll over for their anti-energy agenda—though how much more rolling California can do is unclear, since it has already imposed a go-it-alone cap-and-trade program designed to solve global warming in one state.

The study, published recently in the Proceedings of the National Academy of Sciences (PNAS), is billed as the first worldwide analysis of climate change on wine production. It concludes that a warming world will produce a decline in wine-grape vineyards— as much as 75 percent by 2050—in regions including California, Chile, Argentina, southern Europe, and Australia. The study’s only points of distinction, though, are its purported global scope (which means the margin for error is larger) and its lack of rudimentary knowledge of contemporary winemaking. The great wine scare has been around for quite a while. Spain even hosted an annual “World Conference on Climate Change and Wine,” featuring that well-known climate scientist and oenophile Al Gore, along with former United Nations Secretary-General Kofi Annan, though the series seems to have lost its effervescence after its third meeting in 2011. The current PNAS study is not the organization’s first prediction of a dire future for California’s wine industry. “Climate Change May Bring Sour Grapes,” CBS News reported in 2009 of a similar PNAS study. Still another PNAS study from 2006 explored how “Extreme Heat Reduces and Shifts United States Premium Wine Production in the 21st Century.”

Even if one had complete confidence in long-range climate modeling and ignored the widely acknowledged problems of predicting local and regional effects of projected global warming, the whole exercise serves up some notable howlers. Start with the parochialism of the media coverage. Left out of the news accounts was the finding that the net area suitable for premium viticulture outside existing wine-grape regions would expand by more than twice as much as the area supposedly at risk in California and elsewhere. As the study says, “Large newly suitable areas are projected in regions of Northern Europe and western North America.” Good news for wine consumers, no? It wouldn’t be the first time viticulture has changed along with the climate: 1,000 years ago, after all, wine was made in England and Greenland. (Climate change already appears to be reviving the British sparkling wine industry—don’t you dare call it “champagne”!)

In fact, the chief worry in the new PNAS study is not that wine drinkers will suffer a shortage of quality quaffs, but that the expansion of viticulture into new regions would hinder habitat-conservation efforts on behalf of species that may be struggling to adapt to a warmer world. Here emerges one of the ironies of the climate crowd’s placing so much emphasis on poor California. Environmentalists once complained that California had too many vineyards, and that grape “monoculture” was crowding out habitat. Given the new PNAS portents of doom, environmentalists ought to be celebrating a possible limit to California’s oenophilia; instead, they default to their bigger fear. Climate has trumped everything else for some time now.

Another irony is the study’s speculation that climate change may constrict water supplies for vineyards. This bears a closer look, even beyond the fact that climate models don’t line up uniformly on whether precipitation will decrease or increase in the western United States. Few premium vineyards in California are irrigated; dry farming is the dominant mode of wine-grape production. The study notes that vineyards’ primary use of water currently is for frost-damage prevention in the springtime, when a late frost can wipe out an entire crop if a hard freeze occurs after budbreak. (One study finds that vineyard water use increases as the temperature approaches zero degrees Celsius.) You might think that a warmer climate would reduce the need to counter frost damage.

The study also worries that “water use may increase [in the summer] as vineyard managers attempt to cool grapes [through misting or sprinkling] on the vine to reduce quality loss from heat stress and to reduce drought stress.” Very few vineyard managers employ summer spraying to “cool” grapes, because moisture is the enemy of viticulture. I don’t know of a single vineyard that sprays to cool grapes in my local area on the central coast; vineyard managers to whom I mentioned this idea looked at me as though I was nuts. The premium wine industry has clustered in hot, dry climates for a reason. Vineyards in the more humid northeast are forever treating their vines with sulfur and other drying agents to fight off powdery mildew and other ill effects of moisture. That doesn’t happen often in California.

Might a significantly warmer climate nonetheless make it too hot for grapes in some areas? Even if the climate models turn out to be generally correct (a bad bet at the moment), the models’ lack of local precision makes them useless for forecasting the wine industry’s prospects. Few agricultural enterprises are more dependent on local knowledge of microclimates and adaptation to changing consumer tastes. Even aside from soil composition, an east-facing hillside and a south-facing hillside in the same valley will yield entirely different results, depending on the varietal and the active management of the viticulturalist. No general-circulation climate model could predict what will happen on such a minute scale. Some hillside vineyards calculate harvesting so finely that they pick grapes from the upslope days ahead of the downslope on the same line of grapes, because the effects of daily temperature differences can be measured in real time in the grapes. In the Paso Robles area, whose preeminence in some varietals owes to the region’s having one of the world’s largest diurnal temperature swings, the impact of a generally warmer climate would be lost in the large year-to-year variability that has much more to do with the outcome than the average temperature.

Even more important to all of California’s coastal vineyards are the changes, if any, in predominant sea breezes and coastal fog, which have much more influence on viticulture than general temperatures. And on this point, the climate models lack the “resolution,” as they say in the trade, to make any predictions. A 2011 study of climate and western wine concedes that the current “horizontal resolution is not sufficient to capture all of the microclimatic features that determine temperature suitability.”

In sum, the real world of viticulture bears little relation to the published findings of scientists relying almost entirely on computer models. The latest PNAS study surely won’t be the last episode of the great wine scare. In the meantime, don’t be surprised if premium winemakers “adapt” by using the climate-change craze as an excuse to raise their prices further.


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