warming and its impact on
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
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.
article is modified from a news feature I wrote for leading UK wine
trade journal Harpers.
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