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dimanche, 12 mai 2013



Claude Gilois

What can we learn from the recent past?

In Europe, dates of picking and yields have been recorded for nearly a thousand years and we know that certain periods have been better than others for viticulture as climatic variations are not all due to anthropic changes. It is precisely this point that has provided the global warming sceptics with a lot of food for thought to deny results from the IPCC. It is worth noting that the media at large holds climate scientists to much higher standards than they hold denialists.


We know that warmer periods have alternated with cooler ones. During the Medieval Warm Period that lasted 400 years from 900 to 1300, temperatures were on average one degree higher, and towards the end of the Middle Ages picking took place in early September in Europe, and temperature during the maturation of grapes was 1.7oC higher than that of the nineteenth century. Grapes were cultivated in the South of England and reached as far as the coastal regions of the Baltic Sea. When we observe the speed of recovery of viticulture in areas such as Israel and to a lesser degree Lebanon, where it had been absent for centuries because of cultural reasons, it is worth noting that its re-installation and rising to the top barely takes forty years. We can conclude that areas of previous wine growing can be re-established very quickly and successfully.


This hot period has been followed by what is known as the Small Glacial Age which lasted from 1450 to 1850 and which put an end to viticulture in all northern areas of Europe. Furthermore, reconstruction of temperatures in Burgundy from 1379 and 2003 based on dates of picking has indicated that spells of hot weather seen in the 1990 decade were not unusual and had been seen before. However, a vintage such as 2003 was unique in the history of Burgundian viticulture by its heat intensity and high temperature.


Temperature variations are not uniformly spread out over the globe

An overall increase of world temperature of 0,80C is not uniformly spread out over the planet. We now know precisely what sort of temperature ranges grape growing can tolerate. They obviously vary with every cultivar, but their range of admissible temperature differences between maximum and minimum is fairly small, i.e. 2-3oC. Observation of temperature in Barolo, Burgundy, the Rhone Valley and Beaujolais between 1950 and 1999 has shown that temperature rises were between 0,7oC to 1,8oC with an average of 1,3oC[i], that is 0,5oC above the average temperature increase for the whole world. The increase in temperature has, of course, raised the alcoholic level in wines.  The potential alcohol increase for an Alsace Riesling has risen by 2.5o over the last 30 years and there are statistically significant (i.e. meaningful) correlations with warm periods and with more precocious phenolic maturity.


We can observe the same phenomenon in the Napa Valley where average alcoholic levels have risen from 12,50 to 14,80 from 1971 to 2001[ii]. One has to be very cautious when interpreting rise in alcoholic levels in the USA as a proportion can undeniably be attributed to the American critics who have pushed the wine industry to produce broader, fruitier and more alcoholic wines [iii].  Additional research has shown that global warming has contributed 50% to the rise of the alcoholic levels of the Napa Valley wines [iv].


Europe: The overall winner of the global warming so far?

Is the New World in some difficulty?

At this point, global warming seems to have been more beneficial for Europe than for the New World. Europe has always been a marginal area for viticulture but, then again, the grape does best in marginal climates.  Over the last fifty years, main viticultural regions have seen a better phenolic maturity and sometimes over-matured grapes have been produced in some classical regions.  Barolo and Barbaresco, where the Nebiolo grapes reign supreme, 1997, 2000 and 2007 can be classified as vintages where over-maturity is a dominant characteristic.  Eventhough they have attracted big scores from American critics, they are a significant departure from the classic vintages of Nebiolo, of which 1996 and 1999 can be considered a good example.  However, the number of bad vintages per decade has been markedly reduced over the last 30 years. 


Better climatic conditions have reduced problems caused by adverse climatic conditions such as frost, wind and rain at bud-burst.

In the New World, initially warmer than in Europe, negative effects of global warming have been more noticeable. Australia has seen a drought that has lasted for more than 10 years followed by torrential rain in 2011. In parts of Australia, one can see surrealistic scenes where hundreds of dead trees are bathing in artificial lakes created by the downpours of 2011.    Europe, however, has seen the best of global warming and the worst is yet to come.  It is now obvious that limiting sustainable climatic temperature increase to  20C will not be possible with the current rate of increase in the CO2 concentration, so temperature increases in excess of 20C could mean temperature increases well in excess of that in certain viticutural regions; probably enough to turn the viticulture conditions as we have known them so far, upside down.


I)  Duchenne, E Schneider, C (2005) Grapewine and climatic change : a glance at the situation in Alsace. Agronon. Sustain Dev. 24 :93-99.

II) Vierra G (2004). Pretenders at the Table. Are table wines no longer food friendly? Wine Business Monthly. July 2004: 11(7)

III) Jones GV. (2005). Climatic changes in the Western United States grape growing regions. Acta Horticulturae (ISHS) 689;41-60.

IVJones G.V.. Goodrich, G.B. (2007). Influence of climatic variability  on the US West Coast wine regions and wine quality in the Napa Valley. CLIMATE RESEARCH. Vol. 35: 241–254, 2008.


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