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lundi, 06 mai 2013




Claude Gilois

This is the conclusion reached by scientists in an article published in the Journal ‘Proceeding of the National Academy of Science’ in early 2013 (1a)

Jane Anson, in the English magazine Decanter, was the first to reveal the conclusions of scientists prompting some additional comments by Michel Chapoutier from the well-known producer in the Rhone valley. The article would have warranted some additional comments as articles on climatic change and viticulture are few and far between. It is also a highly emotionally charged subject and over the last few years we have heard all sorts of contradictory points of view. The official position of climate experts has been increasingly challenged by scientists (mostly from fields outside the climatology discipline) who even disputed the existence of an anthropic climate change and calling the climatology a ‘junk science’.

It is obvious that temperature and water supplies are two essential elements for viticulture and any changes in these two variables, as a result of climatic changes, will have a major impact on some of the best-known viticultural regions, in particular in Europe and around the Mediterranean, if we believe the conclusions of the authors.

Before evaluating any article relating to climatic change, it is useful to know where the paper was published and by whom. This article was published in the second most widely read scientific review in the world whose first publication dates back to 1915. It is a peer-reviewed article and the authors come from a field know today as ‘Life Sciences’. They do not have an academic background in viticulture and their study is mostly concerned with the ecological footprints that would result from the transfer of some well-known viticultural areas to new areas more suitable for viticulture.  The  authors have certified that they had no conflict of interest.


They have used 17 climatic models developed by the climatologists to evaluate the impact of climate changes on the major viticultural areas of the world. They have worked on two of the four scenarios[1] proposed by the IPCC[2]. Firstly, they used the  intermediate scenario (also called RCP 4.5)[3] which evaluates the concentration of the major greenhouse gases (expressed in C02) to be 530 ppm in 2050. We are now just about to cross the 400 ppm barrier, the highest concentration since the Pliocene epoch, 3.2 to 5 million years ago. They also use the most pessimistic scenario (RCP 8.5) which estimates the concentration of C02 gas to be 630 ppm in 2050. To day the concentraion of C02 is in excess of the most pessimistic scenario.

The scientists have concluded that the areas suitable for viticulture would be reduced by 19% to 62% with the intermediate scenario (RCP 4.5) and by 25% to 73% with the most pessimistic scenario (RPC 8.5)

Concentration CO2 over time-final.JPG

The 4 scenarios from the IPCC 



c02 concentration and temperature.gif

We know that viticulture is only possible within certain ranges of temperatures which differ for each variety. This range is usually limited to 2oC to 3 oC between the lowest and the highest temperature for most cultivars. It is the Australian Gladstone[ib] who was the first to use this range of variability to identify Margaret River in Australia as being a suitable region for viticulture in the 1970’s, in particular for Cabernet Sauvignon, but it is Jones et al[ii] who, in 2005, identified precisely the ranges of temperature variability permissible for 21 of the major cultivars in the world.


climat maturité.jpg

The regions most affected by climatic changes would be Bordeaux, the Rhone Valley, Italy and most of Spain, and the conditions most suitable for grape growing would move predictably to the north of Europe. The forecast from the models also show a displacement of suitable vineyard land to the north of the USA while the area most suitable for viticulture in Australia would shift towards the east of the country. South Africa would see the disappearance of more than half of its viticulture, as there is no or little vineyard land available at more southerly latitude. New Zealand would be the overall winner of this great re-shuffling of the viticultural deck making viticulture possible all over the islands and south of Central Otago, the most southern latitude for viticulture in the world.   15 of the 17 climatic model results were in high agreement while 2 diverged. The final results were calculated by taking the mean of the 17 models.


Climate change map-FINAL.jpg

The increase in temperature will predictably be accompanied by a water reduction for irrigation and to refresh the vines using giant sprinklers, as it is currently already done in Chile. The most affected regions would be the ones where irrigation is required. Chile would see its water reduced by 47% while water would be reduced by 25% in California, in the Mediterranean basin and around Cape Town.  Australia, already plagued by droughts, would be in an even more critical situation. Australia has already started disengaging itself from industrial viticulture that will become increasingly difficult. In 2050, some of the best viticulture areas in Chile could disappear if the pessimistic scenario 8.5 was confirmed. Maipo, Cochapoal and Colchagua would become largely unsuitable for viticulture, and other regions such as Acongagua and Maule would see production decline sharply. 95% of the current viticultural areas in Chile already experience water stress, the main water resources come from the melting of snow from the Andes and we know that these are very prone to suffer from climatic changes.  Although Argentina is not dealt with in the paper, it is highly likely that its situation is similar to that of Chile.


It is a monumental task to relocate existing viticulture elsewhere as it has a major impact on the local habitat, fauna and flora, and the vines need suitable soil to give their best results. It is highly likely that new terroirs for viticulture would be found outside the existing ones, but the real solution will come from the ability of the winegrowers to adapt to the climatic changes and this is precisely the conclusion that the scientists have come to in this paper. The people who are up in arms about the researchers’ findings should have read the original publication before making their comments.    The effective way winegrowers have to reduce the impact of climatic change is the canopy management as first described by Richard Smart, this is already used extensively in Australia and has proved a very effective way in reducing exposure of the grape to too much direct sun.


It is heat wave episodes that will be more difficult to manage, as was the case in Europe in 2003.  An increase in temperature by 3o or 4oC, if it were confirmed, is not equally spread throughout the year and will produce heat wave spikes with temperatures of 40oC and above.  When temperature increases above a certain threshold, photosynthesis slows down and even stops, and the grapes shrivel on the vine, as was the case in some parts of the Barossa Valley in Australia in 2013.  There is only one region in the world, to the best of my knowledge, where photosynthesis can carry on, despite a temperature of 40oC or more and that is the Hunter Valley in Eastern Australia where rain, sometimes torrential, can beat down during maturation of the grapes. The high natural humidity compensates the high temperature and the region produces very high class Semillon rarely above 11.5% of alcohol. Reducing the temperature artificially with giant sprinklers is an interesting alternative, currently used in Chile, to cool down the vines, but you need water in the first place and in regions where irrigation is needed this is not a foregone conclusion, and the ability of giant sprinklers to reduce temperatures by several degrees has yet to be tested. Water management will have to be better planned to avoid conflicts and the legislation may have to change in Europe where irrigation is largely forbidden.

There is of course another, but more radical solution, which involves uprooting the existing varieties and replace them with more suitable cultivars, but it is difficult to imagine the Rhone Valley being widely planted with Mourvedre, and that Syrah will invade Bordeaux, but some countries may have to resort to going down that path.


Climatic change, until now (about 0,8oC increase over the last 100 years[4]), has contributed to the improvement in the quality of wine made in Europe. The Bordeaux region, for example, produces wines with better phenolic maturity and it is worth remembering that the best vintages of the last century came from warm years (1921,1945,1947,1961). If wine growers were able to cope with a vintage such as 2003, as Michel Chapoutier suggests, it is not a vintage that will be remembered for its greatness, and heat waves such as the one experienced in 2003, are likely to happen 2-3 times per decade; this is not something to look forward to.


An increased temperature of 3-40C could be, at best, a real headache for winegrowers and at worst, a nightmare.  At a time when climatic concerns have been brushed under the carpet by the most polluting countries and any biding agreement not forecast at least until 2015, there is no real reason to be too optimistic.










(1a) Lee Hannaha,b,1, Patrick R. Roehrdanzb , Makihiko Ikegamib, Anderson V. Shepardb,2, M. Rebecca Shawc, Gary Tabord Lu Zhie , Pablo A. Marquetf,g,h,i, and Robert J. Hijmans. Climate change, wine, and conservation (2013) Prioceeding of the National Academy of Sciences.

[1b] These scenarios are called Representative Concentration Pathways (RCPs)

[2] Intergovernmental Panel on Climate Change


[4] CO2 atmospheric levels have been steadily rising for 200 years, registering around 280ppm at the start of the industrial revolution and 316ppm in 1958 when the Mauna Loa observatory started measurements. 


[i] Gladstones, J. (1992) Viticulture and Environment. Winetitles; Adelaide, SA

[ii] Jones GV, White MA, Cooper OR, Storchmann K (2005) Climate change and global Wine quality. Clim Change 73(3):319–343

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