Dra. Liliana Martínez (National University of Cuyo, Mendoza, Argentina)
Currently, the earth is warming. Climate records sufficiently exhaustive demonstrate that warming affects almost the entire earth’s surface. Over the past century and a half, the Earth's average temperature has increased by 0.85°C. Since the 1950s, the increase in temperature has accelerated rapidly, where each of the last three decades has been successively warmer than all the previous decades.
The reality of Climate change is admitted by the vast majority of the scientific community. Climate change is understood as any significant change in the state of climate that lasts for an extended period of time, typically decades, whether due to natural causes or human activities. The IPCC (Intergovernmental Panel on Climate Change) proposes four scenarios of increasing global mean temperatures for the end of this century. The most optimist scenario (RCP 2.6) foresees that the emissions will be decreased drastically in a few decades, while the most pessimist scenario (RCP 8.5) is an extreme scenario without any decreases. Two intermediate reduction scenarios were also added (RCP 4.5, RCP 6.0) (Intergovernmental Panel of Climate Change, IPCC, 2014) (1).
As a consequence of climate change, rainfall amounts have increased at the mid to high latitudes of the northern hemisphere. At the subtropical level, rainfall has declined. Rainfall has increased in South America, northern Europe, and northern and central Asia, while decreasing in the Sahel, the Mediterranean regions and Southern Africa. It seems that wet regions are wetter and dry regions drier as the planet warms.
In addition, the world is experiencing more extreme weather. Although it is difficult to perceive a significant increase in extreme events, trends show a change in the frequency and intensity of these events (e.g. number of cold days, warm days).
Among human activities, agriculture, in particular viticulture, is highly dependent upon climatic conditions during the growing season and wine production.
Vines are grown in a wide variety of climatic situations. However, a majority of the major wine-growing regions are located between the 35th and the 50th parallels in the Northern Hemisphere and between the 30th and the 45th parallels in the Southern Hemisphere. It is virtually impossible to produce high-quality wines in tropical or subtropical regions.
Climate plays a vital role in the terroir of a given wine region, as it strongly controls canopy microclimate, vine growth, vine physiology, yield, and berry composition, which together determine wine attributes and typicity. New challenges are, however, predicted to arise from climate change, as grapevine cultivation is deeply dependent on weather and climate conditions (4).
Climate change will also expose vines to increased drought, either because of reduced rainfall, or because of higher reference evapotranspiration due to elevated temperatures. This may lead to lower yields, because several yield parameters are impacted by water deficits, in particular berry size and bud fertility. On the contrary, water deficit has a positive effect on red wine quality because grape skin phenolics increase and wines develop more complex aromas during bottle ageing.
On the other hand, grapevine phenology (Figure 2), refers to the timing of its growth stages, are very climate sensitive. Higher temperatures advance grapevine phenology. Hence, grapes ripen earlier in the season under warmer temperatures. If harvest occur to early, grapes are rich in sugar, have low acidity levels, promoting unbalance wines, with red grapes containing less anthocyanins. Wines from these grapes will lack freshness and aromatic complexity. Instead, when ripening occurs to late, grapes have high acidity and low sugar contents, with unripe aromas (1).
Hence adaptations to higher temperatures encompass all changes in plant material or modifications in vinicultural techniques with the purpose of delaying ripeness. Later ripening varieties and clones, increasing trunk height, reducing leaf area to fruit weight ratio leaf, late pruning, and moving to higher altitudes. In mountainous areas, temperature decreases by 0.65 C per 100 m of elevation. If other vineyard adaptations are not adequate, and if topography permits (Douro, Portugal; Mendoza, Argentina),moving vineyards to higher altitudes can be an effective adaptation to a warming climate. In Mendoza varieties are grown according to the altitude, where in very warm conditions at 800 m above sea level (a. s. l.) entry-level wines are produced from high-yielding vines. Finer wines are produced from Malbec and Cabernet Sauvignon planted at 1500 m. a. s. l. (Figure 3) and early ripening Chardonnay and Pinot noir planted at 1500 m. a. s. l. (3).
The previously mentioned changes in plant material and viticulture techniques can be progressively implemented. Some of them do not require major changes in viticulture management (e.g., late pruning), while others may involve replanting vineyards with a potential change in wine typicity (e.g., change of varieties). Overall, depending on the rate of climate warming, such adaptations should be effective for decades to come, except maybe for already very hot wine growing areas. (3).
Climate change is a major challenge in wine production. Temperatures are increasing worldwide, and most regions are exposed to water deficits more frequently. Higher temperatures trigger advanced phenology. This shifts the ripening phase to warmer periods in the summer, which will affect grape composition, in particular with respect to aroma compounds. Increased water stress reduces yields and modifies fruit composition. The frequency of extreme climatic events (hail, flooding) is likely to increase. Depending on the region and the amount of change, this may have positive or negative implications on wine quality. Adaptation strategies are needed to continue to produce high-quality wines and to preserve their typicity according to their origin in a changing climate. The choice of plant material is a valuable resource to implement these strategies (2).
1- Etienne Neethlingk, Gerard Barbeau, Cyril Tissot, Mathias Rouan, Celine Le Coq, Renan Le Roux, Hervé Quénol. Adapting viticulture to climate change. Guidance Manual to support winegrowers`decision-making. 2016.
2- Cornelis van Leeuwen and Philippe Darriet. The Impact of Climate Change on Viticulture and Wine Quality. Journal of Wine Economics, Volume 11, Number 1, 2016:150–167.
3- Cornelis van Leeuwen, Agnè s Destrac-Irvine, Matthieu Dubernet, Eric Duchêne, Mark Gowdy, Elisa Marguerit, Philippe Pieri, Amber Parker, Laure de Rességuier and Nathalie Ollat. An Update on the Impact of Climate Change in Viticulture and Potential Adaptations. Agronomy 2019, 9, 514:20.
4- João A. Santos, Helder Fraga, et al. A Review of the Potential Climate Change Impacts and Adaptation Options for European Viticulture. Appl. Sci. 2020, 10, 3092:28.