Global warming is already affecting wine production

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Wine grapes at harvest time in southern France. @bberwyn photo.

NASA, Harvard scientists study wine harvest dates in cool-weather countries

Staff Report

Global warming is changing centuries-old climate patterns that are crucial for wine production in cool-weather regions, a new study from NASA and Harvard concludes. After analyzing climate records and grape harvesting dates from 1600 to 2007, the scientists found that harvests started happening much earlier during the second half of the 20th century.

These shifts were caused by changes in the connection between climate and harvest timing. Between 1600 and 1980, earlier harvests were linked to years with warmer and drier conditions during spring and summer. After that, global warming caused earliers harvests in years without droughts.

from 1981 to 2007 warming attributed to climate change resulted in earlier harvests even in years without drought. The findings have implications for wine production in countries with cooler climates, where high quality wines usually come from years with earlier harvest dates.

The evidence is mounting that climate change is driving the change in harvest dates, said NASA scientist Ben Cook, who led the study.

“Our research suggests that the climate drivers of these early harvests have changed,” said Cook, climate scientist at NASA’s Goddard Institute for Space Studies and the Lamont Doherty Earth Observatory at Columbia University in New York.

In historic patterns, rainfall early in the growing season helps spur vegetative growth, with drier and warmer conditions later in the year helping to complete the ripening of the grapes.

The study looked at 400 years of harvest data from Western Europe, considering  variability and trends in harvest dates, climate data from instruments during the 20th century, and reconstructions from historical documents and tree rings of temperature, precipitation and soil moisture dating back to 1600.

The researchers compared that data with shifts in wine quality in the Bordeaux and Burgundy regions of France based on the ratings of vintages during the past 100 years. Detailed quality information was available for those two regions in addition to the broader harvest data available throughout France and Switzerland.

The results show that the roles of seasonal drought and moisture are changing. Warm temperatures have consistently led to earlier harvests and higher-quality wines in recent decades but the impact of drought has largely disappeared as a result of large-scale shifts in climate.

“Wine quality also depends on a number of factors beyond climate, including grape varieties, soils, vineyard management and winemaker practices,” Cook said. “However, our research suggests the large-scale climate drivers these local factors operate under has shifted. And that information may prove critical to wine producers as climate change intensifies during the coming decades in France, Switzerland and other wine-growing regions.”

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