The Dismal Science

Go North, Young Grapes

The effect of global warming on the world’s vineyards.

In the 1978 Superman, supervillain Lex Luthor bought up worthless dry land in California’s Central Valley. Then, Lex fired nuclear missiles at both the San Andreas fault and New Jersey to prevent the Man of Steel from saving coastal California and to ensure that the villain’s new property would become West Coast oceanfront. The scheme failed, of course. But the idea—that the value of land migrates in the shadow of disaster—has new relevance in light of global warming. Climate change will create lots of winners and losers. Its relationship with land value is the subject of new economic research on an agricultural prima donna: the vineyard.

Grapes require very particular conditions to grow well. For the last few hundred years, European vineyards have thrived between latitudes of 35 and 50, or from Sicily to northern Germany, where temperatures have averaged between 50 and 68 degrees Fahrenheit. Since the last century, the average earth temperature has increased 1 degree Fahrenheit, and according to a 2005 study, wine-quality ratings have improved over the last half-century in the regions where temperatures have risen more. The Intergovernmental Panel on Climate Change expects them to increase between 2.2 and 10 degrees more by 2100. So, what does that mean for where the best wine will come from?

The new study, by economists Orley Ashenfelter of Princeton University and Karl Storchmann of Whitman College, answers this question by using the present-day relationship between vineyard quality and temperature to make informed estimates about the effects of higher temperature on the value of the world’s vineyards. In particular, Ashenfelter and Storchmann have unusual data on vineyards in Germany’s Mosel Valley. OK, it’s not the Loire Valley or Bordeaux, but it sits at the northern edge of the wine belt, near latitude 50. Prussian tax authorities created a detailed land register in the 19th century, classifying vineyards according to eight quality grades based on the average price of wines they produced. The Prussians were tough graders: Of the 344 vineyards included, only 10 percent made the top three grades.

The Mosel Valley is hilly, so the vineyards vary substantially in altitude and latitude as well as slope. And for grapes, slope matters a lot. At the equator, flat land gets the most energy from solar radiation. But at a latitude like that of the Mosel Valley, a southern-oriented hill with a slope of 45 degrees gets 40 percent more solar radiation than a flat piece of land—and just 3 percent less than land at the equator! In the Mosel Valley, vineyards sit on hills that slope in all different directions at different gradients. So, there is large variation in radiation across many otherwise similar vineyards within a small radius. Because of the relationship between solar radiation and earth temperature—more sunshine, more heat, of course—the Mosel Valley is a ready-made experiment for measuring how grape quality will change because of global warming.

When they compared the valley’s vineyards with one another, Ashenfelter and Storchmann found that the vineyards that basked in more sunshine were more likely to produce higher quality wine. Other factors, such as soil quality and altitude, mattered as well. But radiation is extremely important. While only a tenth of Mosel Valley vineyards get a top-three grade, vineyards with 10 percent more solar radiation—based on their slope, orientation, and latitude—have more than double the chance of being rated this high.

Increased solar radiation that raised the average temperature would improve the quality of grapes produced in the Mosel Valley, given its latitude. A planetary increase in temperature of 1 degree Celsius (about 1.8 degrees Fahrenheit) would raise the share of valley vineyards that produce top-three-grade wines (as measured by the Prussian yardstick) from 10 percent to 15 percent. And it would raise the overall value of the region’s vineyards by 20 percent. A 3-degree-Celsius increase (about 5.4 degrees Fahrenheit) would put 28 percent of vineyards in the top-three ranks and double the value of the Mosel vineyards.

The prospect of a warmer planet gives these findings broader application. In Europe, England sits atop the current wine belt, poised along with Germany for expanded viticulture as temperatures rise. In North America, major grape-growing regions extend along the West Coast from Southern California more or less to the Canadian border. So, warmer temperatures will improve the wine offerings of British Columbia. As the temperatures rise, the losers will likely be at the warm end of the viticulture scale—vineyards in Spain, southern France, southern Italy, and the Napa Valley.

For a while, anyway, countries better known for solid automobiles and mounted police may replace countries known for art, romance, and unreliable cars as the world’s premier wine suppliers. A wine renaissance in Germany, England, and Canada could mean that the United States should take action on global warming to uphold the Napa Valley’s honor. Or that Lex Luthor was right, and it’s time to start buying up British Columbia.