Writing in the Oeno One journal, researchers said climate data showed a significant increase in average growing season temperatures in both Napa and Bordeaux, particularly since the 1980s.
So far the warmer conditions have generally contributed to better average wine quality, noted the authors, from the University of Bordeaux’s ISVV Institut des Sciences de la Vigne et du Vin and UC Davis.
Yet, they questioned how long this would continue.
The authors said: ‘In Napa and Bordeaux, viticulture has successfully adapted to a drastically changing climate thus far, but fruit-based metrics raise concerns that we are approaching a tipping point.’
They said previous research showed higher temperatures can increase grapes’ sugar content and decrease anthocyanins, the molecules which help to give red wine its colour. After analysing samples from five vintages of California Cabernet Sauvignon, the authors suggested that colour loss began after a particular sugar level had been reached.
Professor Gregory Gambetta, of ISVV in Bordeaux and a co-author of the Oeno One study, said a key issue was the pace of change and how to find more precise ways of measuring the impact.
‘One thing that’s shocking to me is that temperature change [since the 1980s] hasn’t been gradual,’ said Gambetta in a recent interview with Decanter magazine. ‘We kind of always believe it’s going to be gradual and there’s going to be time to adapt.’
He added, ‘How quickly can growers change if temperatures go up again in another 10-year period?’
While there’s no suggestion of winemakers abandoning signature grape varieties just yet, Bordeaux AOC and Supérieur appellations have gained approval for experimental use of six ‘new’ varieties, including Touriga Nacional.
Gambetta said ‘increasing diversity in any system is always better’, but he also noted that ‘existing cultivars are quite adaptable’.
The authors’ study also cites the economic upheaval that would likely follow a wholesale switch of grape varieties in an established wine region.
Several wineries and vineyard managers have spoken about myriad methods of adapting to climate challenges, although Gambetta said this may require further appellation rule changes in areas such as Bordeaux.
Despite the Oeno One study’s focus on grape quality indicators, he also said quantity of production is a big issue.
Scientists have linked climate change to more frequent extreme weather, such as hailstorms, frost or drought, with the latter also considered a particular risk factor for wildfires.
World wine production in 2021 will be below-average for the third consecutive year, predicted the International Organisation for Vine & Wine last week.
‘This is the result of adverse climatic conditions that severely impacted the major wine-producing regions in Europe,’ said the OIV’s director-general, Paul Roca.
He told a virtual press conference that winemakers ‘have a lot of tools’ to help them adapt to climate challenges, from better data to improved understanding of plant genetics.
Speaking to Decanter last month, Gambetta agreed that plants and winemakers have a remarkable ability to adapt. But, as a plant biologist, one of his main worries about climate impact on wine is ‘not understanding where the thresholds are’.
He added, ‘We are interested in being able to tell growers something concrete.’
A shorter version of this article was originally published in the ‘Uncorked’ section of Decanter magazine’s December 2021 issue.