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Global warming and its impact on wine 

We Brits love to talk about the weather. It’s a safe topic. A little dull perhaps, but safe. And in the last couple of years there’s been a lot of it to talk about, with the scorching hot summer of 2003, near drought conditions lasting through to October and then the dismal summer of 2002 followed by a Mediterranean September and October. It seems that the global weather system is getting weirder and less predictable. Has the human impact on the environment finally screwed our weather up once and for all? This brings us round to the contentious but important subject of global warming, and its potential impact on viticulture.

Important new data suggest that the impact of global warming on many of the world’s leading wine regions may have already had a major influence on wine quality, and will likely have further significant effects in the near future. Recently, Dr Gregory Jones from Southern Oregon University and his colleagues reported results of their analysis of 50 years of climate data from 27 different wine regions and compared them with Sotheby’s 100-point vintage ratings, looking for any trends in wine quality and growing season temperatures. In addition, they ran a sophisticated climate model to look at the projected temperature changes over the next 50 years.

Bad news for the South of France?

But good news for England?

The results are striking. Overall, growing season temperatures have increased for most of the world’s high quality wine regions over the last 50 years, by an average of 2 ºC. In tandem with this rise in temperatures, the quality of vintages has also improved over this period. The study showed a significant relationship between the vintage ratings and monthly average growing season temperatures in most regions.

One potential confounder is that winemaking and viticulture has improved quite dramatically over the last 50 years with the result that what would have been a disastrous vintage some decades ago is now salvageable. In addition, because of the rise in prices of fine wines producers can afford to be more selective, declassifying where necessary – the result is that the overall quality perception of a difficult vintage is improved. As a result, there is the chance that the rise in vintage quality caused by these changes could be mistakenly attributed to the temperature increases. Jones accepts this, but points out that his results show that 10–62% of vintage quality can be explained by growing season temperature variability, with the greatest effects seen in cool climate regions such as the Mosel.

The data also indicate that for many regions, climate has become more variable over this 50 year period. ‘We found that more than half the regions experienced changes in growing season temperature variability’, says Jones. ‘The changes in variability were not uniform, with most of the European regions having the greatest changes.’ Given that the weather towards the end of the growing season, around harvest time, is crucial for vintage quality, do any of the data address how this might have changed? ‘We looked at the “ripening window” period,’ reports Jones, ‘and found that the relative temperature changes mirrored those of the rest of the growing season for most of the regions’.

Perhaps the most interesting part of the study concerns its predictions for the next 50 years. To look into the future Jones and his colleagues used a HadCM3 coupled atmosphere–ocean general circulation model, which has been used previously for predicting changes in agricultural conditions. The results suggest that the 27 wine regions analysed can expect an average growing season temperature increase of 2.04 ºC by 2049. Of these regions, the largest predicted change was for southern Portugal (2.85 ºC) the lowest was for South Africa (0.88 ºC).

While a change of 2 ºC doesn’t sound very dramatic, averaged over a growing season this sort of temperature increase is significant. ‘From this research’, explains Jones, ‘it would appear that the currently cool climate regions would benefit the most. If the climate warms as the models predict, then these regions will be better able to ripen the fruit and may even be able to consider other varieties that could not ripen there today’. He suggests that this might be good news for wineries in England, which experienced a very successful vintage in 2003: ‘Our research indicates that more of the same is in the future for England’. In addition, warmer temperatures could lead to new areas opening up to viticulture.

But the news is less encouraging for some of the warmest wine regions. ‘For many of the warm to hot regions, the negative impacts are already being felt’, Jones reports. ‘In hot regions, grapes ripen to a “sugar ripe” condition, but lack flavours that can take time to develop. Other regions, somewhat in between cool to hot growing climates, will likely have to consider other varieties that will produce better in a new climate regime. For example, in California’s Napa and Sonoma Valleys, the climate has become so warm that ripening fruit is not an issue, but retaining acidity and developing flavour have become increasingly difficult in the warmer conditions. Our analysis shows that this issue could become very critical in already warm areas like Chianti, Barolo, Rioja, southern France, the Hunter Valley, parts of Chile and the Central Valley of California.’

Other effects of increased temperatures could include harvest periods being brought forwards into the warmest parts of the year, reduced water availability, and increased pest and disease burden. So while it seems that the climate change over the last 50 years has mostly had a positive effect on wine quality across the 27 regions included in this study, the future picture could be quite different. And assuming that the projections from the climate models are at all accurate, viticulturalists across the globe will have their work cut out adapting their vineyards to take account of these changes.

These results were presented at the Geological Society of America’s conference in Seattle, and will soon be published in the journal Climatic Change. Dr Jones’ co-workers are Michael White and Owen Cooper. 

This article is modified from a news feature I wrote for leading UK wine trade journal Harpers.

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