Global warming may affect world's finest wines

Global warming may make the famous vineyards of France and Switzerland too hot for traditionally grown grapes, which may affect good quality wines from those regions, researchers warn.

Temperature is the main driver of grape-harvest timing, and in the last 30 years, progressive warming has pushed harvest dates dramatically forward across the globe, from California to Australia, South America and Europe.

In France, where records go back centuries, since 1980 harvest dates have advanced two weeks over the 400-year mean.  These earlier harvests have meant some very good years.

However, existing studies suggest that regions here and elsewhere will eventually become too hot for traditionally grown grapes.

Vineyards may then have to switch to hotter-climate varieties, change long-established methods, move or go out of business.

Scientists analysed 20^th and 21^st-century weather data, premodern reconstructions of temperature, precipitation and soil moisture, and vineyard records and going back to 1600.

They showed that in the relatively cool winemaking areas of France and Switzerland, early harvests have always required both above-average air temperatures and late-season drought.

In the past, droughts helped heighten temperature just enough to pass the early-harvest threshold. Normally, daily evaporation of moisture from soil cools earth’s surface. If drought makes soils dryer, there will be less evaporation, and thus the surface will get hotter.

The researchers said that up to the 1980s, the climate was such that without the extra kick of heat added by droughts, vineyards could not get quite hot enough for an early harvest.

That has now changed; the study found that since then, overall warming alone has pushed summer temperatures over the threshold without the aid of drought. On the whole, France warmed about 1.5 degrees Celsius during the 20^th century, and the upward climb has continued.

“Now, it’s become so warm thanks to climate change, grape growers don’t need drought to get these very warm temperatures,” said lead author Benjamin Cook, scientist at Columbia University’s Lamont-Doherty Earth Observatory and NASA’s Goddard Institute for Space Studies.

The regions affected include familiar names including Alsace, Champagne, Burgundy, Languedoc. These areas grow Pinot Noirs, Chardonnays and other fairly cool-weather varieties that thrive within specific climate niches, and turn out exceptionally after an early harvest.

The earliest French harvest ever recorded - 2003, when a deadly heat wave hit Europe and grapes were picked a full month ahead of the once-usual time - did not produce particularly exceptional wines, researchers said.

“That may be a good indicator of where we’re headed. If we keep pushing the heat up, vineyards can’t maintain that forever,” said Elizabeth Wolkovich, from Harvard University. The study was published in the journal Nature Climate Change.