Can fine wines weather climage change?
(appeared in Mar2016)

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With research and technology the best wines may still get made, says S.Ananthanarayanan.

Grapes are cultivated on eighteen million acres, world-wide, some 750 million quintals are harvested every year and the production of wine, from grapes, is nearly thirty billion litres. In comparison, the world production of wheat is 730 billion kg, or over twenty times as much. But wine commands ten times a higher price, on the average, which makes wine almost equally important a commodity. It is hence of economic, apart from great cultural interest, to examine if global warming, which has threatened the survival of millions and the lifestyle of the rest, would spare this oldest industry of humanity.

Benjamin I Cook, climate scientist from New York and Elizabeth M Wolkovich, biologist and ecologist from Boston and Harvard, describe in the journal, Nature Climate Change, their study of four hundred years of vineyard records, mainly in France, and of one region in Switzerland, and also climate indicators covering the period, to assess the effect that changes in weather conditions have on the time of maturing of grapes, and the implications these changes for the production and the quality of wine.

While alcohol in the wine comes from the sugar content of grapes, the quantity of wine from an acre depends first on the sweetness and the quantity of the fruit. But apart from quantity, it is the quality of wine, as opposed to alcohol from other sources of starch or sugar, which lends wine its special place. And the unique quality comes from the thousands of other substances, acids, esters, aldehydes, aromatics, usually in traces, that form along with the alcohol to make up wine.

Traditionally, the quality of wine has depended on the strains of grape, the nature of the soil, the finely developed process of wine making and, equally important, the timing of the budding of the vines, appearance of berries and their ripening, and also on a warm summer and dry weather later in season. Harvest dates, which are decided based on the maturing of grapes, have been consistently earlier during years with warmer summers, but delayed if there has been rain. And as for the quality of the wine, the records, one source used by Cook and Wolkovich was Michaels Broadbent’s Vintage Wine: Fifty Years of Tasting Three Centuries of Wines, indicate that the best wines came from the years which had earlier harvests.

Growth of vines

In cold countries, where vines have traditionally been grown, budding, or the start of leaves, is soon after winter and a little later, small flower clusters appear. While the energy for the budding is from the previous year’s store, it is the new leaves and sunshine that drive further growth and the development of grapes. The first green berries that form are hard and high on organic acids till they reach about half their final size. At this stage, known as véraison, or ripening, there is reduction of acidity and increase of sugars and also the change of colour when chlorophyll in the green berries gives place to pigments, leading to light coloured or red and black grapes. As the sugar content increases, there are changes in cell structure which limit the uptake of water, so that the sugar content is concentrated.

As can be imagined, a sunny, warm summer, accompanied by a dry later period makes for ample sugar formation and also limits dilution by water, and hence readies the grapes for maturity. “This ensures the vines have sufficient heat and moisture to, grow and mature early on, with dry conditions later in the year shifting them away from vegetative growth and towards greater investment in fruit production mid-season”, the authors say in the Nature Climate Change paper. There has been considerable research, the authors say, into how variations in the weather affect harvest dates and wine quality, but this has been only of recent time scales, some 30-40 years. Understanding how climate change could affect wine production would need study over a longer term, ideally earlier than man-made CO2 emissions started perceptibly affecting the climate, they say.

They have hence made use of an open source, 2012 data base, and a compilation on behalf of the European Geoscience Union, of harvest dates in different wine growing districts in France, Italy, Spain, Luxemburg and Switzerland, from the year 1600. The data base has been created from local vineyard and winery records, the oldest record seen being of 1354 in Burgundy. From this data, the researchers have created a table of average Grape Harvesting Dates over different regions in France (and one in Switzerland). The data of France, for the purpose of estimating the effect of climate change, has the advantage that cultivating practices in France have remained almost unchanged (see box). In fact, the researchers say, even irrigation, which would spoil the study by compensating for climate change effects, has not been used in France

For the climactic conditions, of temperature, rainfall, soil moisture and drought, during all these years, data has actually been recorded since 2001 and this has been used. For the preceding period, they have derived the information from a variety of proxy sources, for example, study of ring formation in tree barks is a record of annual rainfall in the region, over the centuries. For the quality of wine during these years, during which the climate data had been collected, they used, as stated earlier, the 2002 compilation by Michael Broadbent. This record has the advantage of being an estimation of the whole series of wines by the same taster, and hence a consistent standard of assessment.

The result of the data compiled are not basically different from what has been noted, that in the period from 1600 to 1980 and also for the period from 1981 to 2000, years of early harvest correspond to warmer than average conditions, getting more intense in the recent period, when there has been major greenhouse gas induced warming. But the difference – this is the rainfall and the level of dryness or drought – this is consistently low during the good years, with high warming, during 1600 to 1980 – but not thereafter. After 1980, the need for dryness in the later part of the season, disappears – the rainfall is marginally lower, but the drought condition, it actually gets a wee bit wettter!

This change is seen as a major change in the factors that drive maturation of grapes, post 1980. During this period, GHG gas forcing seems to be able to keep up the temperatures needed for grape maturation even without supporting low levels of soil moisture. There has thus been “recent decoupling of wine quality and drought,” the authors say in the paper. These observations, in the regions studied, are generally the same with other regions, they say. This is significant, because the observations are being made over a range of conditions of growth of vines and grape, and sensitivity to changes in climate. Secondly, the consistency across sites rules out changed management techniques being responsible for the trends in harvest dates, rather than forcing by the environment.

It is warm temperatures, thus, that are the drivers for early harvests and quality wines, and the relationship with drought appears to have weakened. This is not to say that drought or moisture would not be relevant, especially in dryer regions than France, there may even be the need for shading of vines when things get too warm, as is done in Australia. And there would always remain the need for monitoring and fine control measures after the grapes are crushed, to take care of the effects a range of causes on the way from budding to harvest. The role of the experience and knowledge at every stage, to guide the wine, and its range of aromas and flavours to perfection has always been valued and the role has been growing in its complexity. The rising temperatures, in the coming decades, in the world’s wine growing regions, would surely call for greater expertise and research to keep the best vintages on our tables even while we cope with other pressures!


Wine making has been something of a scared tradition, carefully controlled and preserved by regional communities in France. The protection of the name, or the appellation, of products, like cheese or wine of a region, has been a practice even before such origin names were protected by law at the start of the last century. The wine growers in a region hence had to abide by norms of a minimum separation between vines, control the use of water (which fattened the grape, but diluted the juice), timely pruning of vines, and so on. Till after the French Revolution, even the dates of harvesting were prescribed by the community or the State.

The use of sugar to improve the quality of grape juice was strongly frowned upon and was even punishable by law. But recourse to adding sugar, during lean years was a necessity, as France would otherwise need to make huge imports if the summer was below par. Jean-Antoine Chaptal (1756-1832), comte de Chanteloup was a man of science, later Minister for the Interior, under Napoleon, who perfected the process of adding sugar to poor grape juice, which was permitted when the vineyard had otherwise followed acceptable procedures. The process is now known as Chaptalisation.


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