 |
...humanity, global warming remains a contentious topic, albeit not nearly as contested as it used to be.
While it’s indisputable that average global temperatures have been rising for the last century, and more specifically over the last 50 years, the problem is that it has been difficult to demonstrate that this is caused by human activity—or ‘anthropogenic’, to use the trade term. Ice cores, long-term temperature records and other clues indicate that the world’s climate has shifted quite significantly throughout history. In recent times, there was a warm period described as the ‘Little Optimum’ in the middle ages, followed by the ‘Little Ice Age’ from the 14th to the 19th centuries, which has only recently receded.
In 2004 Isabelle Chuine of the CEFE-CNRS in Montpellier and her colleagues used historical records of the grape harvest dates in Burgundy to reconstruct spring and summer temperatures from 1370 to 2003. They found two particularly warm decades, in the 1380s and 1420s, followed by a series of warm decades in the 1520s, 1630s and 1680s. After this a long cooling phase began, which commenced with a cold snap in the 1750s, lasting until the 1970s. ‘Our results reveal that temperatures as high as those reached in the 1990s have occurred several times in Burgundy since 1370’, says Chuine.
So could it be that what we are seeing now is merely one of these long-term trends, and that while it correlates with increasing atmospheric carbon dioxide levels, there is no causal relationship? If this were the case, then efforts to reduce CO2 emissions would be a futile and potentially very costly intervention that would hamper economic progress through both the developed and developing countries.
For this reason, climate change is a highly politicised topic. In the absence of scientific ‘proof’—which because of the incredible complexity of accurate climate modelling has not been forthcoming—there has been space for climate sceptics. All that is needed is a few scientists to take a sceptical stance, and that is enough for politicians with motives for downplaying the ‘climate chaos’ story to latch onto. While most of the scientific community has been convinced that emissions of greenhouse gases have had a leading role in recent temperature rises, and as a result many governments have been persuaded to begin enacting legislation, in the United States there has been a strong vein of opposition. But there are signs that this is beginning to change. It’s becoming just as socially unacceptable to disbelieve in global warming as it is to think that women should never have had the vote.
Back to wine. Perhaps more than any agricultural crop, the grape vine is exquisitely sensitive to changes in average growing season temperature. So much so, that varieties have been carefully matched to site, and even within the same region some slopes are fine for one variety but not another, whereas in a neighbouring vineyard with different aspect this may be reversed. Small perturbations in average |
|
|
|
|
|
|
|
|
temperature could therefore have a strong qualitative impact on wine production. So what do the best data suggest is happening to the world’s climate, and how will this impact on winegrowing? The answer is complex, a little uncertain, and doesn’t make cheerful reading.
The most prominent study to address the issue of global warming and its implications for wine was published in 2005 by Professor Gregory Jones and his colleagues from Southern Oregon University. Jones and his colleagues analysed 50 years of climate data from 27 different wine regions and compared them with Sotheby’s 100-point vintage ratings, looking for any trends. They also ran a powerful computer program, the Hadley Centre Climate Model, to look at the projected temperature changes over the next 50 years.
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—so far. There is a significant positive correlation between the vintage ratings and monthly average growing season temperatures in most regions. A confounder is that winemaking and viticulture has improved 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 has improved.
Perhaps the most interesting part of the study concerns its predictions for the next 50 years. The results of the Hadley Centre model suggest that the wine regions analysed can expect an average growing season temperature increase of 2.04 ºC by 2049, on top of the 2 °C rise seen over the last 50 years. This is a highly significant change. The largest predicted change was for southern Portugal (2.85 ºC); the lowest was for South Africa (0.88 ºC).
‘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’.
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.’
In a similar vein to Jones’ work, PhD student Leanne Webb has been conducting a study at the CSIRO in Australia, looking at the implications of climate change for the Australian wine industry. Various climate models and greenhouse gas emission levels were used to predict future climate change in the various Australian wine regions. By 2030, temperature increases of between 0.3 and 1.7 ºC are forecast; Webb equates this to reductions in quality ranging from 12–57%. Her predictions are that the wine industry may have to look to cooler wine regions for new plantings, and change the varieties currently grown in established regions to those better suited to higher temperatures.
Increased temperatures could see harvest periods being brought forwards into the warmest parts of the year, 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, 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. In some cases the careful matching of grape variety to vineyard site may have to be reconsidered.
As well as temperature changes we have to consider climate unpredictability. Agriculture can handle difficult growing conditions, if these are predictable and occur year-on-year.
Seasonal variation is much easier to manage if it can be planned for. However, what seems to be happening is that climate is becoming increasingly unpredictable. Australia is currently in the midst of a devastating drought, and in the previous vintage the Yarra was being harvested before Western Australian wine regions. Most of Europe suffered a serious drought in 2005 after the anomalously hot 2003 vintage and dismally damp 2002. Large variation isn’t consistent for producing quality wines, where specific grape varieties are carefully planted in sites which have suitable average growing season conditions.
A further issue facing a warmer world is that of water availability. While this sounds unglamorous, it could be hugely significant. In most warm climate regions irrigation is the norm; even where this is only used as a last resort for extreme conditions, it is necessary for the establishment of young vines, and to rescue vintages where quality could be lost through periods of water stress.
Finally, there is a significant worry for growers in many parts of Western Europe: what will happen to the Gulf Stream? This is part of an ocean circulation system known in the trade as the ‘Ocean Conveyor’, or the ‘Northern Hemisphere Thermohaline Circulation’, which shifts large amounts of heat from equatorial regions northwards between North America and Western Europe. This ocean flow releases its heat |
|
|
|
|
|
|
|
|
in cooler northerly regions and is responsible for tempering what would otherwise be a much cooler climate. The driving force for this conveyor is the fact that colder water is denser than warm, and saltier water is denser than less salty water. Once this North Atlantic ocean flow, which is very salty, has released its heat, it becomes cooler and sinks, drawing more water from warmer areas and maintaining the flow. What would happen if this water didn’t sink? The answer is that the conveyor would cease. Evidence from ice cores suggest such a conveyor shut-down has occurred several times in the past, leading some commentators to dub it the ‘Achilles heel’ of the world’s climate. If the conveyor were to shut down now, the effects would be disastrous for most of Europe’s wine growing regions, with a drop in average temperatures of up to 5 °C. To put it bluntly, Euope’s wine regions would be ruined. So, paradoxically, global warming could actually prove to be the catalyst for a much colder future for many of us. Signs that global warming has been affecting the vital global conveyor are already emerging. It’s not likely that we’ll see a complete shutdown over the next couple of decades, but this is a possibility we should be concerned about.
The message for winegrowers world wide is that we should be prepared for change. The hope is that this change will be manageable; from current data we can’t be certain of just how it will pan out. The remaining, but diminishing, controversy that surrounds climate change—whether or not it’s all our fault—is more-or-less a side issue here. From the perspective of winemakers, the important fact is that warming is occurring and looks set to continue. It seems likely that increasing temperatures are at least partly to blame for rising alcohol levels in wines from warm climates, which are frequently detrimental to quality. Increasingly, a challenge for growers will be how to manage vineyards to achieve optimum flavour development at sugar levels that don’t result in overly alcoholic wines.
Indeed, even in the classic European regions, the focus is turning away from paying growers by potential alcohol: this was once a reliable and easily measured proxy for grape quality, but it is no longer. Miguel Torres reports that he’s currently buying land closer to the Pyrenees, in cooler climate sites, and that he’s having to adjust his viticulture in existing sites. ‘In the past we wanted to advance maturation to avoid botrytis from the autumn rains’, he explained, ‘but now we are doing the contrary, delaying maturation through density of planting and playing with canopies’. This looks set to be an increasingly adopted viticultural goal in the face of a changing climate.
Winemakers I polled seemed to share a common concern about the impact of climate change. ‘I think there is no question about global warming,’ says Michael Moosbrugger of Schloss Gobelsburg in Austria’s Langenlois. ‘We see it in our documentation about the flowering dates of the past decades. If we take the average, then we |
|
|
|
|
|
|
|
|
can recognize the warming effect. On the other hand, we still have cool (1996, 2001, 2004) medium (1998, 1999, 2002, 2005) and hot years (1997, 2000, 2003).’ Moosbrugger adds that, ‘The prospect is that in the future we will see more warm years than cool years. So how do we react on that? At the moment, not at all. I guess one effect would be that we would slowly become a red wine growing area, for which we would be prepared as we already are growing Pinot and St. Laurent. For vine managment we have to be flexible anyway, as we have to react on the situation of every vintage individually. For the future it also means that we will also look for vineyards that are cooler and higher located in the hills.’
’Climate change is strongly factored in all I am planning’, says Australian wine scientist and winemaker Brian Croser. ‘From Tapanappa’s view point I have a rule, which is not further than 30 kilometres from the coast, not lower than 300 metres altitude and not less than 900 millimitres of annual rainfall.’
‘I’ve been concerned about climate change for more than 20 years,’ says Clare Valley vigneron Jeffrey Grosset, ‘and Gaia Vineyard stands as a somewhat meagre initiative to not only offset the impact temporarily, but was also established from a personal wish that it could, in some small way, raise people’s awareness of the sensitivity of grape quality to the most subtle changes in climate, as is the case with most living things.’ Grosset adds that. ‘The loss of species on earth is of course just making this all so much worse, and the description self mutilation best sums up the impact on us, and other living things.’
‘I am a true believer’, said New Zealand winemaker Steve Smith when I asked him about global warming. ‘It will have a significant effect on us and on winegrowing around the world, the only issue is when and by how much.’ Smith adds that, ‘Whether we are experiencing the effects of it now is debatable. However, in my view the weather patterns seem to be more dramatic. Ironically it seems that frost is playing a bigger part, with the warmer early spring pushing earlier bud burst, yet we are still exposed to the polar fronts that come through and dump late snow and therefore increase frost risk on buds that have burst quite early.’ For various reasons Smith feels that New Zealand will suffer less from the effects of global warming than many other regions, chiefly because it has plenty of room to move south to cooler areas, and because rises in temperature may well make viticulture easier in established regions. ‘To tell you the truth I think New Zealand is very well placed to cope, where our neighbour to the west will have severe problems due to extreme drought, lack of rainfall and increased temperatures.’
Overall, there will be winners as well as losers in the climate change game, but it’s likely that for every winner, there will be scores of losers. |
|
|
|
|
|
|
|
|
