Climate, Viticulture, and Wine … my how things have changed!

Abstract

The planet is warmer than at any time in our recorded past and increasing greenhouse emissions and persistence in the climate system means that continued warming is highly likely. Climate change has already altered the basic framework of growing grapes for wine production worldwide and will likely continue to do so for years to come. The wine sector can continue to play an important role in leading the agricultural sector in addressing climate change. From developing on farm to production to consumer strategies in mitigating aspects that warm our atmosphere, to the wealth of adaptive measures available, the wine industry has and will continue to be at the forefront of these efforts. However, these endeavors will need substantial advances in our scientific knowledge of grapevine growth, productivity, and quality combined with extensive local, terroir-driven, understanding that identifies constraints and opportunities based on regional economies and cultural identities. Finally, it is clear that open access publication is necessary for the timely dissemination of scientific knowledge to other scientists and to the industry.

Introduction

Growing up in the 1970s I became interested in weather and climate while in high school. At the time my teachers were discussing numerous environmental issues, including aspects of climate change. However, the nature of these discussions was quite different than those that we are considering today. In the 1970s climate science was on the fence about whether we were going into an ice age or a warming trend. In a prominent story in the magazine Newsweek (1975) titled “The Cooling World” scientists detailed their concerns about falling global temperatures with terrible consequences for future food production resulting in catastrophic famines worldwide. The article also mentioned that “climatologists were pessimistic that political leaders will take any positive action to compensate for the climatic change.” Sounds familiar, doesn’t it, but today it is for the opposite reason. Another more extensive article came out a year later in National Geographic (1976) with the subtitle “Temperatures change, storm tracks and drought belts shift, as scientists search for answers around the world.” Again, sounds familiar, doesn’t it? In the well-researched article, the author detailed that science was debating whether the world was cooling off and possibly heading into another onset of growing ice sheets and glaciation or was the planet warming irreversibly due to human activities. The major question posed by the article was “what sort of weather will our children and grandchildren know?” I think we see the answer to this question much more clearly today.

As I was heading to college in the late 1980s, the discussion of cooling or warming started to become much clearer. Climate scientists had started to better understand the aerosol effect, whereby sulfur aerosols from the burning of coal from the start of the industrial revolution and the two world wars had contributed to significant cooling during the middle of the 20th century. Climate models from that time were not as advanced as they are today but had started to show that there was real concern for the growing concentrations of greenhouse gases that would warm the atmosphere. Seeing all this unfolding I decided to be an environmental scientist and a climatologist. Needing a dissertation topic for my PhD, I turned to agriculture for my main climatology interests. While many of my professors attempted to direct me to study broadacre crops such as corn, wheat, rice, and soybeans, I had been around wine some and knew that it encompassed so much of life – geography, historical development of civilizations, art, gastronomy, biology, chemistry, economics, geology, soil, climate, etc. – providing a rich agricultural system to study. Looking into the topic further, I found that there were no climate scientists focused on viticulture and wine, and that while the wine industry knew how important weather and climate was, the industry was not looking at it from a climate scientist perspective. The next step was to find where and what to study. Knowing that one needed long-term data for studying climate, I turned to Bordeaux where I knew that there had been records kept over hundreds of years of growing grapes and making wine. As for what to study, my interest turned to trying to understand what aspects of weather and climate influenced vintage productivity and quality, and why certain varieties grew well in some climates but not others.

My research in Bordeaux started with a wealth of data on local and regional weather/climate, grapevine phenology and harvest information on fruit composition and production (e.g., Jones and Davis, 2000). It did not take long to notice that the significant trends in numerous weather factors, especially temperature, were related to trends in many grapevine, fruit, and wine characteristics. This finding piqued my interest on further examining not only the general relationships between growing grapes and wine production and quality, but how a changing climate was influencing the wine industry both in Bordeaux and around the world.

From our early work in this area, it was clear that grapevines were telling us that climate was changing through changes in phenology (Jones and Davis, 2000; Jones et al., 2005a) but that there were also trends in wine quality (Jones et al., 2005b). Furthermore, trends in growing season temperatures had warmed on average 1.3°C during the second half of the 20th century for many of the world’s best known wine regions (Jones et al., 2005b). Additional research looking at other wine regions over a longer period (1901-2018) found that trends averaged 1.4°C for many of the world’s well-known wine regions (Jones, 2019) and that many emerging cool climate regions as far north to 58°N and south to 46°S had warmed on average 1.4°C as well (Jones and Schultz, 2017). In addition, while early climate models had much lower spatial and temporal resolution than we have today, they have been shown to be fairly accurate at what we projected temperatures to be for 2020 (IPCC, 2021).

Recent work by Puga et al. (2022) carried this even more extensively worldwide by examining the general climate characteristics of 813 locations in wine regions during 1959-2018. The research classified the locations into three groups with similar climates and found that temperatures increased, especially in the warmest months of the growing season (99% of the locations), and that daily temperature ranges have decreased largely due to more warming at night than during the daytime. Annual precipitation decreased slightly across all groups, while drier locations got drier and wetter locations got wetter during their respective growing seasons. As a result, higher vapor pressure deficits were seen across all groups and over 93% of the locations examined.

Numerous researchers have followed up our earlier research, confirming many aspects of the relationships between grapevine and climate including widespread trends. Droulia and Charalampopoulos (2022) conducted meta-analysis of scientific publications reporting on viticulture and wine-related impacts in Europe from climate change over the last couple of decades. Their results indicate that increasing trends in temperatures across all regions, declining trends in precipitation in some regions inducing greater water deficits, and shifts in risks from extreme events are the most evident factors. The results highlighted four common themes related to impacts that range from 1) changes in growth characteristics with a longer growing season, earlier phenological timing, more rapid intervals between events, and earlier harvests, 2) to changes in fruit and wine composition and therefore alterations in quality, 3) to varied effects on grapevine yields, and 4) to the expansion of viticulture into regions that were not suitable previously. These impacts have also been documented in other wine regions around the world (Jones et al., 2022).

Others have also helped to fine tune our understanding of the relationships between the grapevine growth characteristics and fruit productivity and quality. García de Cortázar-Atauri et al. (2017) and others have advanced our understanding of the usefulness of quality phenological data to better understand the current distribution of varieties and how more advanced phenological modeling can help us to better understand future climate change impacts. The authors also point to the fact that there is much to be learned about climate’s role in grape composition at harvest and therefore maturity timing. Cameron (2021) found that since grapevine phenology is advancing with increased temperatures, there is often higher sugar concentrations at harvest and/or earlier compressed harvests between cultivars and changes in the synchrony of sugar with other fruit metabolites. Parker et al. (2020) have developed models for both phenology (Grapevine Flowering Véraison [GFV]) and ripeness (Grapevine Sugar Ripeness [GSR]) that help us better understand these relationships and how suitability changes might influence adaptation to new varieties. While these temperature-based models are relatively easy-to-use for predicting flowering, véraison and time to target sugar concentrations (ripeness), I would also argue that these models need to be built with data across more regions with a greater diversity of climate types. Jones et al. (2012) found that only approximately 15% of the worlds wine regions are in traditional Mediterranean climates, while other midlatitude and subtropical dry climates make up roughly 19%, humid subtropical make up close to 24%, and maritime temperate is nearly 13%. Therefore, more climate data across the range of climates that winegrapes are grown in is needed to make these models more universal. In addition, the breath of varieties planted across wine regions needs to be incorporated into these models to be even more applicable. Furthermore, the current prediction error of 6-10 days for phenological events will need to be lowered to be more useful for growers/producers and to better forecast what future changes in climate might bring.

Gambetta and Kurtural (2021), updating the work of Jones et al. (2005b), have asked the important question “are we close to a tipping point” in some of the more traditional wine regions? While both pieces of research indicate that the warming of the last 50 years or more has significantly contributed to increases in average wine quality, ripening relationships and potential wine quality have been shown to be reaching a plateau with concerns for the future. Gambetta and Kurtural (2021) also suggest that fruit-based measures may be better measures of declining fruit quality and tipping points or thresholds under future warming.

Morales-Castilla et al. (2020) have identified that increasing cultivar diversity in wine regions would allow for a measure of adaptation to future climate change as long as broader efforts by society to reduce emissions and avoid higher warming scenarios are realized. Given that there are at least 5000 known varieties grown worldwide and that Robinson et al. (2013) identify 1368 ‘prime’ varieties cultivated around the world for commercial wine production, we have many choices to increase cultivar diversity in wine regions. However, despite the need for increasing the diversity of varieties planted, Anderson and Nelgen (2020) find that the concentration of varieties has increased, where 50% of the world’s plantings are now done with 16 varieties and in new world wine regions it increases to 50% planted to seven varieties.

Still others have helped to further identify potential methods of adaptation with van Leeuwen et al. (2019) strongly suggesting adjusting both plant material and viticultural techniques as climate changes. The authors rightly add that the goal would be to maintain ripening and harvest dates at the end of the season instead of too early, in the warmer part of the summer which disconnects ripening dynamics. In addition, it is recommended that using more drought resistant plant material and modifying training systems to address changing growth characteristics and to consider irrigation where water resources are available and allowed for agricultural use. Santos et al. (2021a, 2021b) provides a summary of the work from a European Union project titled “Clim4Vitis”. This work describes adaptation potential over both the short-term and long-term while noting that there many uncertainties, particularly in the long-term, which could alter the best responses depending on region and specific impacts from climate change. The authors state that unravelling these uncertainties was critical to the sustainable development of the wine industry. Short-term adaptation examples from this research include alterations to canopy management, the application of various sunscreen materials to either the plant or the whole vineyard, supplemental irrigation where available and feasible, focused soil management in warmer and drier conditions, and more integrated pest and disease control at the whole vineyard and region scale (Santos et al., 2021a). The work identifies that the long-term adaptations often require greater structural changes and therefore greater investment, which growers and producers are more reluctant to adopt. These include changes in training systems, alterations in the plant scion and rootstock material, changes in cultivars, and relocation of the vineyard (Santos et al., 2021b).

Naulleau et al. (2021) in a systematic review of adaptation strategies for viticulture has helped to identify that many potential site-specific trade-offs are likely to occur. The authors argue that both scientific and local knowledge is needed to develop better spatial and temporal tools to assess the appropriate adaptations to the local conditions. They highlight the need for more multi-scale studies to identify local constraints and opportunities, but also more in depth and systematic economic studies on the impacts of the various adaptation strategies. One such method to address these needs and better understand what the future might hold, the wine industry could use more work like that of Remenyi et al. (2020) which resulted in a climate atlas for all of Australia. The atlas uses the latest climate projections for Australia’s wine regions and provides growers/producers detailed information about how the climate may change over the near, mid, and long-term time horizons over this century. Having tools like this, that are both regionally focused and built with the best data possible, provides the scientific knowledge base from which management decisions for adaptations can be scaled to local knowledge (Naulleau et al., 2021).

Conclusion

Combined, weather and climate are the most basic and most profound environmental factors in grape growing and wine production. Together they drive the overall suitability for viticulture and matching specific cultivars to individual sites, they largely determine what wine styles can be produced in each area, they drive substantial crop risk factors, and produce vintage variations in production and quality. Historically, wine regions have developed worldwide where the weather and climate were most conducive. But the weather and climates of wine regions vary greatly with some more at the climatic margin, some with warmer days and some with warmer nights (differences in humidity), some drier and some wetter, some with relatively reliable rain during the growing season and others with very little, some being more prone to risk from weather extremes, while others are more equitable and consistent. As such it begs the question: Is there a weather/climate structure that is best suited for a given variety for optimum wine quality and production? Then, within the realm of a changing climate, when and how will these weather/climate structures change beyond what is considered viable for both varieties and regions?

From a climate science perspective, my how times have changed … From the second half of the 20th century to today we have gone from concerns about global cooling due to aerosols to evidence of unequivocal warming in the climate system and changes in numerous aspects of weather and climate (IPCC, 2021). While changing atmospheric concentrations of greenhouse gases are the most evident influence on our warming climate, the sum of human impacts on the Earth’s energy balance from deforestation, desertification, urbanization, and ocean acidification mean that future changes are highly likely. With warming across the Earth’s surface, in the atmosphere, and across the world’s oceans, along with declining amounts of snow and losses in ice mass along with rising sea levels the United Nations’ Intergovernmental Panel on Climate Change estimated that to avoid the worst climate impacts we need to limit warming to 1.5°C by the end of the century, but that to do so the magnitude of emissions reductions need to approach net-zero.

A portfolio of mitigation, adaptation, and geoengineering options will be needed across society writ large to meet the UN’s limits on warming and emissions. Mitigation is necessary to limit further warming, and since agriculture is both part of the problem and part of the solution, on farm mitigation efforts will be needed. For vineyards the greatest opportunity to reduce GHG emissions is the reduction of carbon-based energy sources, followed by managing and reducing nitrogen fertiliser applications, and enhancing soil carbon sequestration. But on farm mitigation measures need to be supported by infrastructure, for example to shift to more renewable energy we need more robust power grids that could store energy more efficiently. Estimates point to needing at least a hundred times more storage by 2040 if we want to shift largely to renewables. On the winery to consumer side, mitigation efforts are most focused on reducing packaging weights but also capturing onsite emissions, developing onsite alternative energy sources, and facilitating more efficient distribution of products. In terms of adaptations in the wine industry, for vineyards most of the conversation is focused on changing to more suitable varieties or moving locations. But this loses site of the myriad adaptations described above that have enormous potential to sustain vineyards and wine production over both short- and long-term time scales. Geoengineering, also known as climate engineering, is the deliberate large-scale processes that would attempt to counteract climate change. Geoengineering is largely focused on solar radiation management and carbon dioxide removal, with most of the IPCC (2021) modelling scenarios relying on some degree of carbon dioxide removal to limit warming below critical limits.

What have we learned in terms of influences from a changing climate on viticulture and wine production? Warming of 1-2°C has occurred in wine regions worldwide since the middle of the 20th century. Changes in extremes are becoming more evident with increases in heat and drought stress, along with an increased risk of wildfires and smoke impacts. Grapevines have also been showing change with earlier phenological events. As such, during warmer late winters and springs, earlier growth has brought greater risk from frost in many regions. Shifts have also moved ripening and harvest into a warmer portion of the summer, accelerating sugar ripening, but disconnecting other ripening clocks, and leading to harvest compression between varieties in many regions. As such ripening profiles (challenges in managing timing of sugar, acid, flavor, and phenolic development) and wine characteristics have changed with wine styles in some regions becoming more full-bodied, fruit-driven, often with higher alcohol.

The planet is warmer than at any time in our recorded past and increasing greenhouse emissions emissions and persistence in the climate system means that continued warming is highly likely. Climate change has already altered the basic framework of growing grapes for wine production worldwide and will likely continue to do so for years to come. Should we be pessimistic or optimistic? From my perspective, life is full of possibilities and to not be optimistic closes the door on the possibilities. As such, the wine industry needs to be diligent, smart, and innovative to build resiliency in our production systems, which will increase our adaptive capacity, and reduce our vulnerabilities to climate change today and into the future. Science has a significant role to play in developing the awareness needed to make smart decisions. First, it is clear that open access publication is necessary for the timely dissemination of scientific knowledge to other scientists and to the industry. Second, we should be challenged to continue to grow more advanced weather and climate studies in viticulture and wine production, developing more robust observation networks, and building models that cover the breadth of varieties and climate types suitable for viticulture and wine production both today and into the future.

Acknowledgment

I wish to thank the many people in the Bordeaux that opened doors for me to gather the data necessary to do my PhD research, which ultimately provided the basis for my entire research and teaching career. I would also like to thank the entire collection of researchers worldwide examining climate aspects of growing grapes and making wine. You have all made my career rich with interactions and brought a wealth of knowledge to our science and to the wine industry.

References