The heat has brought the harvest earlier and earlier

A recent study by the European Geosciences Union successfully demonstrated a correlation between the rise in average temperatures and the earlier harvests. They did so by using the recorded data collected from the Burgundy wine region since 1354. The study calculated that between 1354 and 1988, the average start date for the harvest was around the 28th September. Since 1988, the year when the inflexion of the temperature curve took place and the temperatures started to increase by more than the average, the average start date for the harvest is now 13 days earlier, on the 15th September.

It’s not just the hot summer temperatures and heatwaves which cause the grapes to ripen faster (sometimes the heat can have the opposite effect and block the maturity), it’s the average temperature throughout the year that is making each stage of the vine’s development earlier.  The bud burst, flowering, and veraison are all happening earlier, as a study by INRA France Agrimer showed in 2017 (donwload the chart – in French).

The impact of the heat on the harvest

As we just mentioned, the winemakers must reorganise the way they work in the face of climate change, not just for the harvest, but in the methods and techniques used in the vineyard throughout the year. All of the green work is challenged. For example, when the summer is forecast to be hot, the winemakers remove much less leaves than before, so as to not burn the grapes by leaving more shade. The tops of the vines are trimmed more severely to reduce the surface area of foliage, thus limiting the photosynthesis that causes the grapes to ripen too quickly. 

And even before this stage, some winemakers opt to spread mulch in the vineyard as opposed to mowing the grass.This creates a vegetative layer that limits the evaporation of water when it is hot. Research is also under way in some regions to evaluate the planting of grape varietals that mature later and are less sensitive to the heat.

We can also note that other climatic conditions are also impacting the vines.  When the winters are warmer, the bud burst happens earlier, and so any late frosts are more likely to cause significant damage to the buds.  Hail falling from thunderstorms, and droughts are becoming more frequent and intense, increasing the risk of reducing the yield. And then there are new diseases and parasites that are appearing with the warming, as well as shortening the reproductive cycles and the number of generations of insects each year.  The eudemis grape berry moth and leaf hoppers are good examples.

Even without all of the above, a summer drought can drastically reduce the yield because, without water, the grapes don’t swell enough and produce less juice to ferment.

The quality of the wine evolves and the characteristics change.  With heat, the level of sugar in the grape must increases, and can give wines with a higher alcoholic degree and less acidity.  For red wines, sometimes it is a characteristic that is sought after, allowing the wine to have stewed fruit aromas rather that fresh fruit.  But it is generally much less desirable for white wines because you need a certain freshness and equilibrium with the acidity.

A few avenues to explore in the face of rising temperatures

In terms of the work in the vineyard, we have already touched on some of the techniques that can be used to fight against the heat and lack of water.  As well as research into new types of grape varietal, studies are underway to produce rootstocks that are more resistant to drought.

On the winemaking side, you can also compensate for the lack of acidity by choosing yeast that is able to produce less alcohol from the same amount of sugar, or by using tartaric acid, although these methods are of course less naturel.  You can also remove some of the alcohol by filtering it through a membrane, but this can also alter the taste of the wine.  Filtering is also possible before the fermentation to remove some of the sugar in the juice.

These procedures are just avenues to explore for the moment, and are not completely satisfactory in that they act in response to the initial problem, that of rising temperatures and global warming.  But they are worth exploring given the acceleration of the rise in temperature over the past few years, as the winemakers are likely to face bigger and bigger threats to their harvest over the coming years.

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Never has the wine been so good and the situation so dire. The tone is set. For the two authors, both specialists in the fields of climate and the environment, the question is not whether climate change will happen, but how the French and global wine industry will deal with it.

The change is already happening, and the statistics and proof of climatic change abound. Since the temperatures in the vineyards have been recorded, the five years with the highest average temperature in the vineyards are 2000, 2005, 2010, 2014 and 2015. Worryingly recent. That supports the view that the climatic phenomena are accelerating, and the exceptional frosts a few weeks ago in the Loire and Burgundy will not stop the trend. The rainfall levels are completely disrupted and the temperature changes even more violent.

As Valéry Laramée de Tannenberg explained, the wine growing regions have encountered numerous climatic change events over the centuries, and that is notably why the culture of winemaking, born in Persia, has climbed further and further north to escape the mounting temperatures in the south. This was also enabled by the advancing Roman legions, known to be great wine lovers, as they expanded northwards. What is different today is the speed of the climatic change. During the COP 21, we talked about trying to stay below 2°C of temperature rise between now and 2100. If we continue as we are at the moment, we are already approaching a rise of 1.5°C.

And the impact for winemaking is already being felt. In the south of France, we're seeing wines touching 16°C in terms of alcoholic volume because of over ripeness. The heat is such that the grapes contain a sugar level that is too high. That is also posing problems for managing the harvest, which is starting earlier and earlier, and which sometimes calls for harvesting during the night to pick cooler grapes. It also has an impact on the vines themselves. In the Bordeaux region, researchers have shown that the merlot grape varietal has reached its optimum. Within the current conditions, it does very well, but a further increase in temperature will see yields decrease. The vines are also seeing new attacks from parasites and fungi which the heat encourages. The wine regions are continuing their advance north, and we are seeing a growth in the number of vineyards in England for example.

The wine growing regions are suffering and it's all of the industry that needs to adapt. Even if some of the changes haven't always been anticipated, there are currently a few paths to explore. The first attempts have been made to try and reduce the alcoholic volume in wine. Tests have been carried out to prune the vines differently and to leave more leaves on the vines to protect the grapes from the sun. Other tests have seen the orientation in which the vines are planted rotate or by planting vines at a higher altitude. In some of the wine growing regions outside of France, where it's authorised, the wine can be diluted with water or filtered when pressed to remove some of the sugar.

But the most impactful research for the long term will be that which is undertaken on the selection and diversity of the grape varietals. In the Bordeaux region for example, they are testing 50 or so new grape varietals which are not currently authorised in the Bordeaux AOC range of wines. Another promising avenue is the regeneration of the soil to develop the micro-bacterial activity as is already the practice with biodynamic winemaking. And another area of research is looking at genetics to create hybrid plants that mature later and are more resistant so as not to need phytosanitary treatments.

To conclude, not is all yet lost if we accelerate the change in cultural practices by using the advances in agro-ecology, organic and biodynamic farming techniques. To learn more about these proposed solutions, you can read more in the book « Menace sur le vin : les défis du changement climatique » (French language only for the moment).

The question that lingers as I leave the conference is the following. The winemakers will encounter some big challenges in the years ahead, but what can we, as consumers and lovers of wine, do? One solution that quickly comes to mind is to be more interested to better understand and better choose our bottles, favouring wines that are produced in an environmentally responsible way. And to talk with those close to us about our choices, so they talk to those close to them, and so that a tiny ripple becomes a wave big enough to force change upon the rest of the wine industry!

Marie Koch

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