Wines & Vines

26 WINES&VINES February 2018 Viewpoint T emperatures 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 Intergovernmen- tal Panel on Climate Change. 15 Despite the worldwide rise in temperatures, many ag- ricultural 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 par- ticular." 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 Don- ald 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 con- straint to operating your vineyard? The winegrower's reply was rather torrid. To my simple question about viticulture con- straints, 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, cli- mate has a greater impact on vine development and fruit composi- tion 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 typic- ity for that region. Those drivers are changing. J. Glad- stones, 8 R. Roehrdanz and L. Hannah 16 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 viticul- ture include temperature, moisture stress and radiation. 10 The phenology of bud break, flow- ering and véraison are temperature-depen- dent 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 ripen- ing. Sugar concentration increases with temperature, although secondary metabo- lites such as aroma, flavor and phenolic com- pounds are generally negatively affected by high temperatures. 12 Vine water status depends on soil tex- ture, percentage of stones, rooting depth, rainfall, evapotranspira- tion and leaf area. 19 Water de- ficiency affects photosynthesis and shoot growth; it can in- crease both tannin and antho- cyanin content, 6 while excess stress can lead to leaf damage and severely impair fruit ripen- ing. The proper cover crop may help assure ground shading n DR. BRUCE ZOECKLEIN How Climate Change Affects Winegrowing

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