February 2018 Issue of Wines & Vines

How Climate Change Affects Winegrowing

by Dr. Bruce Zoecklein

Temperatures will increase between 2.0º and 2.5º C (3.6º-4.5º F) by the end of the century, with the worst-case scenario being an increase of 3º-3.5º C,3 according to estimates by the Intergovernmental Panel on Climate Change.

     Despite the worldwide rise in temperatures, many agricultural products will continue to be cultivated without any noticeable difference or change discerned by consumers. This is not the case with the wine industry, where wine quality may be impacted. According to Spanish winemaker Miguel Torres, “Climate change is the greatest threat for the wine business in general, and for winegrowers in particular.”14 The reality of climate change and man’s influence is admitted by the vast majority of scientists, vignerons and the general population, with the notable exception of Donald Trump, a man who wanted to be president in the worst way—and perhaps is.

     My first glimpse of the impact of climate change occurred during a trip to Romania sponsored by the U.S. Agency for International Development in the early 1990s. I was traveling on one of Romania’s state-of-the-art medieval roads to meet a vanguard, one of the country’s more renowned winegrowers. Unfortunately, his lack of English competency was eclipsed only by my lack of Romanian. Through an interpreter I attempted a conversation by asking the vapid pedestrian question: What is your most important constraint to operating your vineyard?

     The winegrower’s reply was rather torrid. To my simple question about viticulture constraints, he replied, “My favorite time of year is mid-way between the flood and the drought,” or what I would later term “the universal grapegrower’s mantra.” As it turns out, it may not be the change in climate that is the greatest concern, but rather the unpredictability of the weather.

Climate and vine physiology
Among environmental factors, climate has a greater impact on vine development and fruit composition than either soil or variety.18 Each main wine-producing region of the world can be characterized by mean climatic conditions that are drivers of wine typicity for that region. Those drivers are changing. J. Gladstones,8 R. Roehrdanz and L. Hannah16 summarized some of the overall effects of a changing climate:
• Increased temperature during the growing season,
• Increase in growing degree-days,
• Increase in mean temperature during fruit maturation,
• Increase in mean temperature of the warmest month of the growing season,
• Increase in mean temperature of the coldest month of the growing season,
• Increase in length of growing season (frost-free days),
• Occurrence of extreme winter minimum temperatures,
• Increases in precipitation for July through October,
• Increase in precipitation seasonality (coefficient of variation),
• Change in the aridity index (annual precipitation/potential evapotranspiration).

     The primary climate vectors impacting viticulture include temperature, moisture stress and radiation.10 The phenology of bud break, flowering and véraison are temperature-dependent and well established. In some regions, the intervals between these events have decreased as a result of climate change.2,13 Temperature affects the rate of fruit ripening. Sugar concentration increases with temperature, although secondary metabolites such as aroma, flavor and phenolic compounds are generally negatively affected by high temperatures.

     Vine water status depends on soil texture, percentage of stones, rooting depth, rainfall, evapotranspiration and leaf area.19 Water deficiency affects photosynthesis and shoot growth; it can increase both tannin and anthocyanin content,6 while excess stress can lead to leaf damage and severely impair fruit ripening. The proper cover crop may help assure ground shadingand contribute to humus formation while helping to buffer very dry and very wet periods.

     Many Europeans equate limited soil moisture with their terroir expression and remain reluctant to irrigate. It should be noted, however, that many of these vineyards are on abundant underground aquifers. In many other regions of the world, aquifers are very deep, and thus the water is unavailable to vines.3 Climate variability may necessitate even more careful monitoring and, perhaps, more irrigation.

     Ripening is dependent on a constant supply of hormones. Optimum hormone balance is dependent on continuous and moderate moisture stress and favorable soil temperatures. Therefore, irregular patterns of moisture stress and increased rainfall will certainly have an impact.
     Another possible effect of climate change is diurnal temperature range (difference in temperature between day and night), which will decrease as carbon dioxide levels increase.1,8 Such changes can influence fruit secondary metabolites such as aroma, flavor and phenolic compounds. Large differences in clouds, humidity and diurnal range—particularly in mid-latitudes and continental interiors—will continue to occur with a changing climate.
Winemaking issues
Processing changes may need to be considered for both red and white cultivars. The following are a few winemaking issues that may be impacted by climate change:
• Vintage-to-vintage variation,
• Ripeness assessment,
• Tannin and color,
• Longevity/reductive strength,
• Grape nitrogen,
• Grape/must temperature,
• Alcohol adjustments,
• Need for flexibility in practices.

Vintage variation
Climate change may result in minimal impact on terroir expression due to the multitude of influences of geography, topography, soil and underlying geology.3 However, some varieties are impacted more than others with regard to warmer temperatures and seasonal variations. Tight-cluster grapes are much more prone to fungal diseases, as are thin-skinned varieties compared to thick-skinned varieties. Varieties such as Viognier, Petit Manseng and Tannat have proven to do well in the warm, humid environment of Virginia.

     Vintage-to-vintage variations are likely to become much greater, as seen throughout the world. It is not climate change, per se, that will affect some, but the erratic nature of the unpredictable weather that may be a greater problem. Increased seasonal variations may influence fruit set and will affect maturity and maturity evaluations. We can expect the asynchrony among primary (such as Brix) and secondary metabolites (aroma, flavor and phenols) will likely increase. Additionally, as a function of changing environmental conditions during fruit set, fruit variation within otherwise uniform blocks may increase.

     Even in the most uniform vineyard, the coefficient of variation for various components is broad at best: Brix 4%-5%, TA 10%-12%, berry weight 6%-20% and color 13%-18%.9 These ranges will certainly increase in some areas and will require great sampling precision.

Ripeness assessment
In 2016, Boris Champy reported that harvest dates for his Pinot Noir at Louis Latour in Beaune, France, had moved from mid-October to approximately Sept. 20.4 D. Frederick Frank reports that his New York vineyard has experienced a 10% increase in growing degree-days (GDD) in the past 10 years.7 One obvious contribution of global climate change is the tendency in some regions to pick grapes at slightly earlier ripeness. Optimally, this should occur following the loss of green tannins in the fruit.

     Animals, insects and plants have moved to higher elevations and more northerly climates to adjust to warmer temperatures. It is likely that viticulture will follow a similar pattern in the future.3 Some grapegrowers have chosen to plant vines at higher altitudes to find cooler ripening climates. This can impact heat and, likely, ultraviolet interception.

Tannin and color
Red wine cap management strategies and skin contact time must be reviewed in the context of changes in seasonal variability and fruit chemistry. (See “Climate Can Impact Phenol Concentrations at Harvest” on page 28.)
     Differences in phenols are both qualitative and quantitative. The major quantitative differences due to climate lie in the ratio of anthocyanin to skin tannins at harvest. This ratio is important due to the influences on color, color stability, mouthfeel and aroma integration.

     During fermentation, oxidative condensation reactions occur, resulting in tannin polymerization. This continues until a terminal polymer end reacts with an anthocyanin molecule, stopping the process. Thus, anthocyanins act as bookends, limiting chain elongation. As such, the more anthocyanins there are relative to tannins, the shorter the resulting polymers and the “finer” the tannins. Thus, seasonal variations that impact this ratio also impact the resultant polymer length.

     Tannin-anthocyanin polymers help stabilize color. Small polymers have relatively fewer protein-binding sites, thus producing less astringency. These small colloids provide a surface area that allows for integration of aroma components. Additionally, climate change can impact the concentration and type of color cofactors, components that bind with anthocyanins providing additional spectral color.

Longevity/reductive strength
Small pigmented polymers help provide red wine reductive strength. Reductive strength is essentially a measure of the uptake of oxygen, providing longevity, or the ability of a wine to age. This is an important quality attribute, analogous to a wine’s chi (qi), or life force. Reductive strength is impacted by both climate and fruit maturity. Problems with under-ripe fruit include the following:
   • Insufficient pigments,
   • Limited extraction,
   • Limited desirable flavors, which limits tannin capacity.
The problems with over-ripe fruit or wide variations in fruit maturity include the following:
   • Loss of color,
   • High alcohol capacity, which can destabilize color-tannin complexes,
   • Significant loss of reductive strength.
     The change in phenolic content as a function of excessive fruit maturity can lower the reductive strength by a factor of 10.17 In some regions, the use of hyperoxygenation for some white cultivars may become more important in helping to provide longevity. (See Enology Notes #160 at vtwines.info.)

Grape nitrogen
Both YAN (yeast assimilable nitrogen) and micronutrients are essential for fermentation. Nitrogen availability can be considered a terroir factor, being correlated to both red and white wine quality, particularly where soil moisture is not limiting.

     Fruit nitrogen may change notably in some regions as a result of increases in temperature and precipitation extremes. As such, it may be even more important in the future to monitor each block, each season, for nitrogen status. This monitoring should be done in concert with the understanding of differences in optimum YAN in red and white grapes, cultivar differences and difference between native plant-derived nitrogen and fermentation adjuncts.

Grape/must temperature
The importance of energy management should be highlighted as a result of climate change. Many regions around the world have sustainability programs to help winegrowers understand the importance of sustainable practices including thermal control. These programs will become even more important to the industry in the future. Winemakers and winery owners should understand that energy is a variable, not a fixed cost. Each producer, large or small, interested in saving money should answer the following questions:
   • What is the relationship between energy cost and your bottom line?
   • How is energy used at your facility, and where?
   • What are the ways to reduce energy consumption?
   • Are you benchmarking or measuring your energy use?
     The advantage of benchmarking or determining your energy use lies in the ability to answer these questions by measuring, contrasting and charting progress. It is like the old saying: “If you do not know where you are going, any road will take you there!”

Many regions have experienced increases in sugar concentration, resulting in potential alcohol elevation of 1% to 2%. However, others have noted that the average sugar level at harvest has not significantly changed over the years, suggesting that grape sugar level is not only dependent upon weather, it is influenced by a multitude of other factors including yield.
     Research on additional methods for alcohol removal, and the selection and creation of yeasts that produce less alcohol, will certainly continue.

Industry strategies and flexibility
There is an old expression that suggests advice is free unless it is followed. Below are recommendations for adjusting to the ever-changing reality of climate change:
   • Be flexible, not formulaic, with vineyard/wine processing regimens.
   • Use and share scientific information.
   • Be out in the vineyard.
   • Invest in wine and grape research.

Smoke taint
There may not be a better example illustrating the need for research investment than smoke taint. Climate change and how forest land has been managed has resulted in an increase in the incidence of forest fires.5 The fires have added a relatively new term to the winegrower’s lexicon: smoke taint. Smoke residue contains high concentrations of volatile phenols such as guaiacol and eugenol. The glycosylated forms of these phenols tend to accumulate in the grape skin and pulp. These compounds are released during fermentation, causing wines to become unpleasantly “pharmaceutical,” “dirty,” “medicinal” or “burnt,” with “ash tray” and “campfire” characteristics that reduce the perception of fruit aroma intensity.

Climate change dilemma and science skepticism
Some people have been under the impression that in U.S. society no one should suffer; we all work together for common benefits, and once a danger is understood, the problem will be addressed. That is, the government will work to protect all of our citizens. Unfortunately, that has not been true with regard to climate change.

     Capitalism acknowledges that there will be destructive consequences to the pursuit of private prosperity and financial gains. Corporations suggest that they did not mean to pollute the river but are quite pleased to have someone else pay to fix it. However, what do we do if it is not a river, but the entire planet being degraded as a result of human-induced climate change?

     Curtis White (author of Science Delusion) asks: “Are taxpayers going to have to pay for a new planet?” He suggests that the oligarchs and their supporters (the so-called 1%, the highest income individuals in our society) have a Faustian view, but they are not stupid. Their habitude is to do nothing about the changing climate because they do not want to, and because the threat of destruction is not persuasive to them. They are quite pleased to have others pay for any corrections that may be needed. It would appear that their motto isPereat mundus dum ego salvus sim: Let the world perish as long as I am safe. But they are no safer than you and I; they simply value their wealth and the status quo.

     Directly and conclusively linking climate change to weather has admittedly been difficult, a fact the heretics point out on a regular basis. But asking for direct scientific evidence in this case is like attempting to vindicate that poor eyesight or arthritis are caused by old age. They are not, but they are certainly related.
I believe the argument for and against man-made climate change is reminiscent of Pascal’s Wager. Blaise Pascal was a French fideistic philosopher who proposed a wager to his colleagues who did not believe in God. The wager, and you had to bet, was his way of demonstrating the importance of seeing the world the way you would like it to be.

     Pascal wrote: “You can wager there is no God. If you are right, what do you gain? Absolutely nothing. What do you lose? Infinitively everything. You can bet there is a God, and if you are wrong, what do you lose? Absolutely nothing. If you wager there is a God and you are right, what do you gain? Infinitely everything including eternal salvation. Faced with the choice of no detriment and such a gain, who would not at least want there to be a God?”

     The analogy seems appropriate. What do you (and the rest of us) lose if you bet against man-made climate change and are wrong? Everything, including a livable planet! Only when the deniers and capitalists are brought on board will significant progress be made.

     Mahatma Gandhi discussed the concept of svadharma outlined in the Bhagavad Gita. The idea is that that each member of a society has a collective duty, a responsibility, indeed an obligation to work to bring forth the values he or she endorses. The modern equivalent: If you are not part of the solution, you are part of the problem!

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Dr. Bruce Zoecklein is enology professor emeritus at Virginia Tech in Blacksburg, Va.

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