Global Warming and Wine Quality: are we close to the tipping point?

Written by Professor Gregory Gambetta for JA

To coincide with COP26 in Glasgow, we asked Professor Gregory Gambetta, an expert in viticulture, to summarise the findings of a rigorous scientific study that he has been involved in, looking at whether the benefits for viticulture of a warmer climate on viticulture, that have led to more regular grape ripening over recent decades in areas such as Bordeaux and Napa, is now approaching a point where the negative effects outweigh the positive. A link to the full scientific study can be found at the end of this article.

The worlds’ top wine regions have grown out of – among other things – exchanges between grape cultivars and the local climate, resulting from a long history of interaction between the two. Growers, scientists, and wine professionals speculate that global warming could reshape the distribution of these regions, pushing them to higher latitudes and elevations with cooler temperatures. It goes without saying that these redistributions have the potential to be economically devastating.

This scenario is based on the idea that specific wine grape cultivars each have an ideal temperature range within which they produce the best wines. We assume that climate change will determine regional winners and losers. The winners will be the regions where warming allows for increased quality winegrape production, and the losers will be where quality wine grape production becomes impossible because it is simply too hot. The United Kingdom is a great example of a current winner, with rapidly expanding production and reputation. But in well-established regions how much warming is too much? Are viticultural scientists good at predicting the temperature thresholds that will result in poorer quality wines?

These are the questions we asked in a recent article “Global warming and wine quality: are we close to the tipping point?” published in the open access journal Oeno One. The study examined the relationships between warming, ripening, and wine quality over the past 60+ years in two of the world’s top red wine regions, Napa Valley in California, U.S.A. and Bordeaux, France.

Not surprisingly both regions have warmed substantially over the past six decades with the average growing season temperature increasing by 2°C in Napa and 3°C in Bordeaux. What is remarkable is that these increases have not been gradual, but instead the temperatures increased abruptly during the 1980s. Scientists recognise the 1980s as a period of extreme climate change referred to as a “regime shift”. These abrupt changes were felt globally; the timing of the cherry blossom season became earlier, tuna migrations changed, and winter snowfall amounts decreased. What’s alarming about this precedent is that temperatures can change rapidly over short time frames. Viticulturists, enologists, and policy makers need to be prepared to adapt quickly to future climate change.

But how have grapes and wines changed over this period? Wine quality has not been negatively affected but instead has become more consistently good. There are probably numerous contributors to the increased quality. Increased temperatures have resulted in riper fruit with higher sugar concentrations, viticulture and wine making techniques have evolved, and consumer preferences have changed towards riper flavors with less vegetative aromas. The worst fears of the wine industry have not come to pass, but if we assume that warming will continue, is there a tipping point?

A seminal study from the late 1990s predicted an optimal average growing season temperature of 17.3°C for Bordeaux. However, Bordeaux surpassed that temperature more than a decade ago and is currently a whole degree warmer. Perhaps our inability to accurately predict these thresholds shouldn’t be surprising. Both plants and humans adapt. But importantly how can we make better predictions?

So far most predications have been based on wine quality scores which are subjective and subject to changing preferences. Instead, fruit-based metrics may be better indicators of losses in grape quality. We found that the dynamics between the accumulation of sugar and colour (i.e. the important quality-related phenolics, anthocyanins) exhibit a clear peak where both are maximised. Interestingly this peak corresponds to about 13-14% potential alcohol, after which color decreases. Similar relationships exist for other quality-related compounds.

What is clear from the study is that so far both Napa and Bordeaux viticulture has successfully adapted to a drastically changing climate. The current challenge is to better predict the thresholds that will lead to decreasing yield and quality in the face of climate change.

Gregory Gambetta is a professor of viticulture at Bordeaux Sciences Agro and the Institut des Sciences de la Vigne et du Vin.

The full article can be read here: https://oeno-one.eu/article/view/4774