Wine grape harvesters will feel the heat if climate change carries on - study
Connoisseurs of fine wine should be drinking a toast to global warming, according to new research.
They say every cloud has a silver lining. In the case of climate change, the welcome news is that higher temperatures in France are producing exceptional vintages.
But scientists have warned that if the trend continues too long, the current run of outstanding grape harvests could end.
Records dating back more than 500 years show that wine grapes across France are now being harvested two weeks earlier on average than they were in the past.
Wine grape maturation is accelerated by warmer temperatures and delayed by rain, and earlier harvests are generally associated with higher quality wines.
The main reason for the change is climate change pushing up temperatures in the absence of drought, it is claimed.
Dr Elizabeth Wolkovich, from Harvard University in the US, who took part in the research published in the journal Nature Climate Change, said: "There are two big points in this paper.
"The first is that harvest dates are getting much earlier, and all the evidence points to it being linked to climate change. Especially since 1980, when we see a major turning point for temperatures in the northern hemisphere, we see harvest dates across France getting earlier and earlier.
"The bad news is that if we keep warming the globe we will reach a tipping point.
"The trend, in general, is that earlier harvests lead to higher-quality wine, but you can connect the dots here .. we have several data points that tell us there is a threshold we will probably cross in the future where higher temperatures will not produce higher quality."
There is a French word, "terroir", that vintners use to describe the set of environmental factors affecting wine grape quality.
It is because of terroir that the wine grape is one of the best barometers of climate change, say the scientists.
"At the heart of a good wine is climate," said Dr Wolkovich. "So the grapes are a very good canary in the coal mine.
"You want to harvest when the grapes are perfectly ripe, when they've had enough time to accumulate just the right balance between acid and sugar.
"For much of France, there have been times when it's difficult to get the exact harvest date growers want because the climate wasn't warm enough that year. But climate change means the grapes are maturing faster."
In the past, early wine grape harvests have always required both above-average air temperatures and the added kick of a late-season drought, leading to warmer, drier soils and rapidly maturing grapes.
Prior to the 1980s, droughts were necessary for early harvests - without them, vineyards could not quite get hot enough.
Since then, overall air warming alone has pushed summer temperatures over the early harvest threshold, the research shows. Throughout the 20th century France warmed by about 1.5C, and the upward climb has continued.
Lead author Dr Benjamin Cook, of the US space agency Nasa's Goddard Institute for Space Studies and Columbia University's Lamont-Doherty Earth Observatory, said: "Now, it's become so warm thanks to climate change, grape growers don't need drought to get these very warm temperatures.
"After 1980, the drought signal effectively disappears. That means there's been a fundamental shift in the large-scale climate under which other, local factors operate."
The wine-growing regions affected included some familiar names, among them Alsace, Champagne, Burgundy and Languedoc.
Vineyards in these areas grow finicky Pinot Noirs, Chardonnays and other varieties that thrive within specific climate niches and are especially good when they can be harvested early.
"So far, a good year is a hot year," said Dr Wolkovich. But she pointed out that a foretaste of what might be to come occurred in 2003 when a searing heat wave led to the earliest French grape harvest ever recorded.
In that year, grapes were picked a full month ahead of their usual time. However, the wines they produced were mediocre.
Dr Wolkovich added: "That may be a good indicator of where we're headed. If we keep pushing the heat up, vineyards can't maintain that forever."
Across the world, experts have found that each degree Centigrade of warming brings grape harvests forward roughly six or seven days.
A 2011 study led by Dr Yves Tourre, from the Lamont-Doherty Earth Observatory, suggested that a combination of natural climate variability and human-induced warming could force Pinot Noir grapes out of many parts of Burgundy.
Other reports indicated that Bordeaux might lose its Cabernets and Merlots.
One controversial study published in 2013 predicted that by 2050 some two thirds of today's wine regions may no longer have climates suitable for the grapes they now grow.
As the world gets hotter, famous-name wine grapes might find unlikely new homes, possibly even making southern England the new Champagne region, according to some experts.