What it means to winegrapes and what we can do about it

I'm not an expert in climatology, and I’ll bet most of you are not either. That is why I listen to experts on the subject of climate change. I concluded, long ago, that not only is it real, but humankind has played a large part in the most recent and dramatic changes in weather patterns and weather-related events. I’d like to avoid politics in this viticulture column, but I find it painful to hear that deniers are still out there. Sure, there are some scientists that deny anthropogenic causes for climate change, but they represent only a tiny minority of scientists who have seen enough evidence supporting man-made climate change. In fact, many of the scientists being touted by climate change deniers are not climate scientists at all—some are not true scientists at all.

What struck me and made me a believer many years ago, was the dramatic spike in atmospheric CO2 concentration over the last several decades relative to levels in the distant past. According to a National Aeronautics and Space Administration (NASA) graphic,1 over hundreds of thousands of years CO2 levels fluctuated between 200 and 280 ppm, based on data collected from ancient ice cores. In 1950, CO2 spiked to more than 300 ppm and continued to rise to its current level of over 400 ppm. So don’t tell me that humankind isn’t, at least in part, the cause of an extreme and rapid rise in CO2 unlike any other in the last 800,000 years or so.

CO2 isn’t the only greenhouse gas (GHG). According to Environmental Protection Agency (EPA) graphics,2 methane levels fluctuated about a mean of 500 ppm over that same time span and have spiked in recent decades to about 1,800 ppm. Nitrous oxide, a persistent and strong greenhouse gas, fluctuated above and below a mean of about 250 ppm over that long stretch of time and has risen to about 330 ppm in the present time.

Yes, humans have created these changes, and one does not need to be a climatologist to understand that the burning of fossil fuels by an ever-in-creasing population has caused this change. It both surprises me and sickens me that there are still people who buy into the propaganda that these are normal phenomena we are witnessing. But I said I wouldn’t get political…

What is Changing and What Does it Mean When Growing Winegrapes

I attended the Sustainable Ag Expo in November 2019 and listened to two speakers on the topic of climate change. Tapan Pathak, an extension specialist researcher at UC Merced, is a specialist in climate adaptation in agriculture. He stated that while temperatures are rising, the maximum daily temperatures are rising only modestly while the nighttime minimum temperatures are rising at a higher rate over time. A paper in which Pathak was lead author3 showed that an 11-year running average of California temperatures has risen above the long-term average by about 1° F since 1980, but the recent decade saw deviations from the mean up to and over 2° F. If you think that only 2 degrees doesn’t mean much, think again. Over the growing season, that level of increase kicks a region up a whole notch in the Winkler classification.

Warmer night temperatures will have an effect on fruit maturation that is distinct from daytime temperatures, so the phenomenon of rising temperature minima should not be taken casually. Photosynthesis occurs only during daylight hours for the grapevine, but vine and berry metabolism continues to take place during the night. Berry metabolism uses malic acid as its primary source of energy, so warmer night temperatures should stimulate a more rapid degradation of malic acid, leading to fruit with lower acid concentration at harvest. On the other hand, secondary metabolite production could potentially increase as well, which could have the effect of a faster phenolic maturation rate under warmer night conditions. Hence, higher night temperatures could be detrimental to warmer regions while having a potential benefit to growers in the coolest of regions. That benefit could be swamped out in the bigger picture, however, as growing seasons could be shortened both by temperature increases and more dramatically changing weather conditions during the growing season.

Gregory Jones, professor and director of the Evenstad Center for Wine Education at Linfield College in the Willamette Valley, Ore., spoke at the Expo and stated that a 1° F increase in average temperature would shorten the season from budbreak to harvest by between five and 15 days. That means that fruit may get riper sooner and, as a result, could ripen during the warmer summer months, further amplifying the wine quality issues associated with a warmer environment.

Jones cautioned that increases in temperature would likely be accompanied by increases in humidity, and, therefore, disease pressure could be on the rise. Has anyone noticed that recently? I know that powdery mildew incidence and severity seem to be increasing almost every year, and I also have noticed higher humidity affecting stomatal conductance (higher humidity leads to higher stomatal conductance). Apparently, climate change has not led to overall increases in precipitation but has led to, and will continue to lead to, more dramatic weather events in the form of not only severe storms, but also intense cold, extreme heat and increased occurrence of drought. Although temperatures are rising globally, we don’t talk much anymore in the vernacular of “global warming.” Warming is certainly occurring, but it is the dramatic events occurring worldwide that are of greater environmental and societal impact. Hurricanes, fires, floods and other catastrophic events are beyond the scope of this discussion, but variable weather conditions are certainly impactful on wine growing.

Changes in weather from year to year are to be expected as a natural part of our wine-growing world and are often viewed as the primary influence of vintage quality. But as climate change intensifies, the variability from year to year increases, causing larger and larger deviations from the mean and potentially creating more and more poor vintages due to extremely cool weather or extremely hot weather. One does not have to look very far back to recall the 2017 growing season (very hot) followed by 2018 (very cool). The 2017 North Coast fires notwithstanding, 2017 was a difficult growing season that featured sluggish and stopped ripening due to sharp changes in temperature. Yes, weather varies, and much seasonal variability is simply natural changes in weather, but we will likely face greater variability as time goes on and climate changes worsen.

What Should We Do as Growers?

As climates warm and region II’s get transformed into region IIIs (and so on), varieties that have performed well historically may not be ideal any longer. Jones said he is seeing that in the Willamette Valley, though they have some time to go before Pinot Noir doesn’t work there. But, outside of the U.S., wine-growing regions in Europe and just northward into Canada have experienced such changes in climate as to consider varietal changes. For the Okanagan Valley of British Columbia, that means that Bordeaux varieties may be grown successfully in its southern reaches. That may be a welcome occurrence for them, though I know that there are very few who are actually excited about the prospects of climate change. Although research is ongoing to find alternative varieties for existing wine regions, how can Napa not be known for Cabernet Sauvignon? And who would want to see a Russian River Bordeaux blend? Regions have developed identities, and a change in climate that upsets that identity could be a marketing nightmare and a real disruption to our industry—an industry that maintains deep ties to history and tradition. That said, it may be inevitable that some varietal changes be made, at least in the warmer parts of each region. In cooler parts of each region, warmer-climate varieties will likely begin their intrusion into formerly cooler-climate vineyards.

More subtle vineyard changes can be considered, especially in the cooler parts of each region that are not yet ready for varietal change. Trellis systems that provide more shade on fruit will likely become more popular, bucking the longer-term trend of strictly upright VSP trellises. Cross-arms to widen out those tight VSPs have been showing up more and more, though the benefit of widening the trellis has little effect on fruit shading unless row orientation is such that fruit becomes shaded during the hot, late-afternoon sun. Hence, vineyard design for new vineyards is as important now as ever—and likely more important. For existing vineyards, leaf removal practices may need to change, though the trend towards lighter leaf removal could potentially backfire into causing higher disease incidence. Plastic mesh shade cloth that covers the fruit zones from hot afternoon sun is becoming more common, and it seems that a black shade cloth, which provides about 30 to 35 percent shade works well in most cases over other colors and densities.

Irrigation management cannot be done by calendar or in the same manner every year. Rainfall patterns, especially spring rainfall in the North Coast, will dictate when irrigation needs to be started. Growers must look at weather forecasts to apply preemptive irrigations to avoid vine stress during heat waves. This is not that different than it ever was before, only it is more imperative than ever that growers stay on top of irrigation management and not follow the same pattern each and every year.

What Can Growers Do to Stop Climate Change

We can’t stop climate change; we can only slow it down. It will take dramatic shifts in our behavior and our reliance on fossil fuels to stem the tide. As individuals, the answer would be to initiate behavioral changes on a personal level, but that is of infinitesimal impact if not done broadly by the whole populace, not only by our country but by all countries, including those that are heavier contributors to GHGs than the U.S. So, yes, the answer is political, and it’s not an ideological one necessarily (though it seems to be right now). There are members of all political parties who support changes to reduce GHGs, and they must be supported; they, in turn must support changes worldwide, including those bad actor countries that continue to emit GHGs at a higher rate than our own.

As for growers, our impact is slightly more influential than that of an individual outside the world of agriculture. We burn diesel to farm, burn vines and trees when they are removed for replanting, and we till the soil. All of these contribute GHGs to our environment and in a much bigger way than the average Joe.

I don’t see us getting away from diesel tractors anytime soon. The amount of horsepower required for farming is high, and currently only diesel engines provide sufficient energy to run our implements. While the newer tiers of diesel engines are cleaner burning than they used to be, reducing particulates, carbon monoxide and oxides of nitrogen, they still spew about as much GHG as they used to; it’s just that some of the other side-effects have been mitigated. I have yet to see an electric tractor in action, but they are on the way. About 10 years ago we would have scoffed at an electric car, but look at what we have now. Electric pickup trucks are on the way, and aside from the satisfying rumble of a full-size pickup truck, they will eventually be able to get the job done.

On the other side of the equation, vineyards sequester carbon, which is something we do that provides a benefit to the environment. Carbon is sequestered in the vines themselves but is also found in the soils where cover crops grow and decompose, leaving carbon skeletons that persist for long periods of time. The actual amount of carbon sequestered is now being studied in detail, and it is a meaningful amount. But we can quickly undo that benefit if we burn our vines after we tear them out for replanting. All of the carbon in the biomass of the permanent vine structure is released back into the atmosphere when vines are burned. Chipping is an alternative that avoids this rapid carbon release. It is considerably more expensive than burning, since wires and other hardware need to be separated from the vines instead of simply pushing them into a pile and burning. But its benefits should not be overlooked for sustainable, carbon-neutral winegrowing.

Perhaps even more detrimental than vine burning is tillage. Yes, good old tillage. While it seems logical to till a cover crop under to allow it to break down in the soil, tillage actually introduces a large slug of carbon into the soil that is rapidly decomposed, compared to the same vegetation in a no-till condition. Tillage destroys the soil structure and microbial ecosystem; it not only leads to a rapid release of CO2 into the atmosphere, but also causes a large release of nitrous oxide. Nitrous oxide is a more detrimental GHG than CO2. Reducing or eliminating tillage from our vineyards could go a long way towards improving carbon sequestration and GHG reduction.

While we represent only a small fraction of agriculture worldwide, winegrape growers are dedicated to sustainability, and we can and should set examples for all of our agricultural brethren. True sustainability extends past one’s own farm.

Check out Mark's full article in the April issue of Wine Business Monthly.