by Karl H. Kazaks
Scientists tell us that the extreme weather conditions we’ve been seeing in recent years are part of a greater pattern of climate change which also portends a future of increased mean temperatures, greater extremes in temperature, and altered precipitation. With warmer temperatures, polar ice is expected to continue to melt and sea levels will consequently rise. The chemical composition of the seas is also expected to change. Greenhouse gas composition will continue to change.
But what about viticulture? How will it be affected by global climate change?
A study published this spring in the Proceedings of the National Academy of Sciences suggested that climate change will have substantial impacts on viticultural systems, possibly leading to conflict over land use and water.
The report, whose lead author Lee Hannah is an ecologist at Conservation International’s Center for Applied Biodiversity Science and an adjunct faculty member at UCSB’s Bren School of Environmental Science and Management, suggests that the temperature rise associated with climate change may cause vineyards to be relocated to higher latitudes or elevations, impacting current ecosystems. What’s more, the author projects that water use in vineyards may increase as misting becomes more common as a tool for regulating vineyard temperature, thus increasing pressure on fresh water supplies.
The authors modeled climate conditions under different rates of climate change and came to some stark conclusions. Under one model, for example, the bulk of the prime viticultural valleys in Chile (including Maipo and Colchagua) will become unsuitable for wine grape production by 2050.
The report also suggest that the upper part of North America’s Rocky Mountain — from ‘the Yellowstone to Yukon’ — could become a major wine producing region. The suitability of growing grapes in that region, the report said, “is expected to increase by a factor of 19 by 2050.” Its authors worry that vineyards in this region may not “be compatible with movements of animals such as pronghorn and wolves.”
But what about today? What can grape growers do today to protect their vines, their industry, their livelihood? Will they be able to survive without moving into the path of grizzly bears?
To answer this question, Wine and Grape Grower spoke with experts in the field to get their view on how climate change will affect viticulture, as well as suggestions for tools and strategies growers can use today to mitigate against climate change both today and in the future.
Dr. Stuart Weiss
Dr. Stuart Weiss, the founder and chief scientist at Viticision (and founding partner in another firm, Creekside Center for Earth Observation), uses his environmental biophysics background to provide modeling, analysis, and design solutions for vineyard clients.
He consults to various wineries, including Treasury Wine Estates, and has worked on wineries from Santa Barbara to Mendocino. His work with wine grapes focuses on phenology — “the timing of organism development over the season,” he explained — and how it is affected by climate change.
“Grapevines are exquisitely sensitive to temperature,” he said. “When do they break bud, when do they flower, veraison — all of that is affected by temperature.”
Using the John Gladstones’ concept of biologically effective degree days (the total amount of heat experienced by a vineyard, which can be calculated by known latitude, altitude, vineyard slope and inclination to the sun, soil type, geography, and average minimum and maximum temperatures during the growing season), Weiss takes measurements in vineyards to determine how a certain site’s phenology is expected to develop. With such measurements, Weisss calculates “the expected date of ripening” for a vineyard or block.
“The system is incredibly sensitive to small changes in temperature because they accumulate over the season. You can get a shift in harvest date of a week or earlier on average on just a small temperature rise.”
With climate change, Weiss said, “the basic change you can see and a lot of people have come across this: the increase in temperature means you ripen earlier. When you ripen earlier you ripen at a warmer time of the year.” That matters because temperature and final ripening is an important indicator for wine quality. To have a nicely balanced wine, you want to have your sugars, acids, tannins and phenolics simultaneously ripening.
Of course, every growing season is different and rarely is every variable at an ideal state during harvest. Tools of winemaking can correct for subtle imbalances, but the goal is to have the best grapes possible, requiring the least intervention in the cellar.
To model how a vineyard will respond to real-time climate variables, Weiss likes to have at least a year’s worth of data from that vineyard. He’ll wedge tiny thermometers which can store data into grape clusters and let them collect data all season. Then he’ll compare the data they stored to the local weather station and build a model.
With such models, he can make historical climate reports as well as project ripening dates for current vintages.
He also uses hemispherical photography (sometimes called canopy photography) to quantify the light environment experienced in a vine’s fruiting zone. “We call it the grape’s eye view,” Weiss said.
It works by putting a camera in a vine and aiming it toward the sky. It measures how much solar radiation comes through. With that information, Weiss can make suggestions to how to alter canopy management.
“Grape growers,” he said, “have a large toolbox” for adapting to climate change. You can change canopy management, with a trellis retrofit (such as adding cross arms). How much modification you can make in this way is limited, Weiss noted, by your need to be able to move tractors and other equipment through vine rows.
If you’re ready to replant, you can adjust your row orientation. If you’re happy with your vineyard design but feel like the variety you’re growing there is not suited to the climate you can even regraft to new varieties. With regrafting, you typically have to wait only one year to harvest fruit.
“It’s a tricky decision making process,” to determine how you want to change your vineyard to adapt to climate change, Weiss said. But it’s a process that is much better done with more information — hence Weiss’s work to provide vineyards with data.
For growers with a wide portfolio of vineyards — in different locations with different attributes — it’s important to recognize, Weiss said, that climate change is something to consider not just on the micro-scale of grape cluster temperature and canopy management decisions but also on how to balance one vineyard versus others.
For example, if you have a commitment to a certain variety (take Merlot), you will want to plant it along “a temperature gradient,” Weiss said, so the risks of climate change are reduced. That will ensure that in warmer years the cooler sites will produce desired grapes while in cooler years the warmer sites will do that same. Not having all of your Merlot vines in one type of climate environment will ensure that you don’t have a single vintage (or repeated vintages) of substandard harvests because of climate conditions affecting grape quality.
“It’s not just about a single vineyard,” Weiss said. It’s about all of your vineyards, and “there’s a lot of moving parts there.”
The bottom line in making decisions about grape growing based on climate change, Weiss said, is “it’s important to be systematic.” Having more information — whether it’s climate modeling data or consumer preference trends — makes being systematic that much easier.
Weiss acknowledged that with interannual swings in climate, “picking out the larger climate signal is hard. The trend can be masked unless you have decades to study it.” But there is a general, non-uniform warming trend.
“The big question temperature-wise is the rate of change, not the direction” of change, Weiss said. With warmer temperatures there will be earlier ripening dates, during warmer times of the year. There is also a general trend toward more extreme temperatures — this year’s West Coast heat wave being an example — which can affect grape quality because, Weiss said, some parts of the growing cycle are “very sensitive to excessive heat.”
How will these changes affect wine quality, assuming climate’s affects on grapes are too big to be countered in the cellar or by steps taken in the vineyard. Weiss expects wines to be more out-of-balance, lower-acid wines being made with grapes harvested when sugars are ripe but before the berries reach full phenolic maturity.
Despite the challenges climate change will bring to grape growing, Weiss is hearted. “Growers are always dealing with big differences in interannual weather,” he said. So they’re already well-equipped to make adjustments.
What’s more, as we see warmer temperatures, so too will we see “a lot more opportunities for viticulture,” Weiss said.
Like Weiss, Tim Martinson is seeing earlier harvests — in his case, in the Empire State — due to warmer temperatures and faster ripening. 2010 and 2012 were among the earliest harvests ever in New York.
Martinson, senior extension associate in Cornell’s Department of Horticulture whose research includes sustainable production and the impact of cultural practices and climate on grapes, said the earlier harvests tend “to be good for vines,” because it gives them more time post-harvest to collect nutrients and prepare for winter.
“We have a fairly short season now, often only a week or two of green leaves on vines after harvest,” he said. If they have more time with leaves on their vines after harvest, they can spend energy collected from the leaves “funneling carbohydrates to roots” rather than to nurturing berries.
If temperatures continue to rise in New York, Martinson said, “My suspicion is you’d see different varieties replacing the ones we have — possibly more reds — but it’s still going to be a coolish climate.”
What may change, if New York becomes more like Washington state, is that growers may be able to harvest bigger crops, thanks in part to higher degree days.
Martinson has noticed that with warmer temperatures the date at which vines become winter hardy has become later and later. Because the risk of earlier arctic cold spells has not gone away, in New York there is consequently, Martinson said, a “slightly increased risk for winter injury.” That’s because a fierce cold snaps might come in December — something that used to be more common — when the vines aren’t quite yet winter hardy, like they might have been previously.
Likewise, there is also heightened springtime risk of frost damage thanks to early bud break and subsequent frost events. That’s prodded Martinson and others to look for ways to slow down bud burst in the spring.
Even with warmer mean temperatures, Martinson doesn’t recommend growers forego protecting their graft unions. “I think everyone should hill up,” he said.
Martinson is not as concerned about vineyards moving northward to take over ecosystems used by wildlife. Instead, he thinks that vineyards will move northward but to land that is already in agricultural use.
Even with climate change-related effects such as more extreme precipitation, he’s confident grape growers will be able to withstand climate change. “Growers adapt their management every year,” he said. “They have to.”
What are some adaptations they might make?
Like the authors of the report in the Proceedings of the National Academy of Sciences suggest, they could start sprinkling or misting water to manage vineyard temperatures.
They could also use fans to control temperature, screens to control temperature and light exposure and protect from possible increased hail events, as well as any number of strategies to contend with climate change-related altered disease pressure.
They could move to night harvest to control fruit temperature, or start using cover crops (if not using them already) to retain moisture and lower soil temperatures.
They could switch to more drought-tolerant rootstock.
In Napa and Sonoma, many vineyards are being renewed following a major replanting in the early 1990s when vines then planted on AxR1 rootstock started becoming damaged by phylloxera.
Garrett Buckland — a partner in Premiere Viticulture, a Napa-based vineyard consulting firm — pointed out that grapes grow everywhere on Earth except the two poles. One of the biggest factors determining whether a particular variety can grow in a certain region is rootstock. Buckland expects new rootstocks will be developed to help overcome some of the effects of climate change — whether consequences of warmer temperatures or lesser or more varied precipitation.
Vineyard design, too, is key in managing the effects of climate change. When Buckland designs a vineyard, he thinks about “building in flexibility” to allow vineyard managers to contend with possible climate change factors.
One of the most important parts of design is row orientation, he said. In Napa and Sonoma — not counting for slope, geography, or site-specific characteristics — the best orientation is between 35-45 degrees off of true north, depending on fog influence. Planting on that diagonal, said Buckland, allows for a balanced heat exposure on both sides of the canopy.
A balanced heat load is important, Buckland said, because heat is a big threat to the qualities that determine varietal character. Sauvignon Blanc, for example, will lose its aromatics at high temperatures.
Trellis design is another important way Buckland manages temperature and sunlight. Whites tend to need more coverage, and in a generally warmer environment you want a trellis which will allow more canopy coverage on the fruit.
Many of the vineyards being replanted now in Napa, Buckland reports, are going in as a modified VSP with some kind of spread canopy at the top. That requires more canopy work, but it can also buy an extra hour’s worth of canopy protection every day.
Buckland is optimistic about the wine industry’s ability to meet the challenges of climate change. “With smarter vineyard practices and smarter winemaking, we’re changing the question,” of how climate change will affect grape growing and wine making, he said. “If you do nothing — if you’re in Europe and have AOC rules tying hands,” for example, it’s much more likely your winemaking will suffer from climate change. But when you have flexibility you can adapt.
“You’re always on your toes as a viticulturist,” he said. The 2011 vintage in Napa, he pointed out, was one of the coldest in a long time, while the 2013 is shaping up to the warmest on record.
Water use is of course one major way to respond to weather. Buckland and his firm are proponents of what they call “big drink irrigation,” giving soils larger amounts of water much less frequently. “When you step back, in some cases you just might not need to water at all.
“When we really look deeply at water management we find that a lot of vineyards can use less water and make better wine. They’ll get similar crops yields at potentially better quality — sometimes exponentially better quality — wine.”
Contending with invasive pests and diseases will be a challenge for growers as climate change proceeds, Buckland said. That’s not just because new diseases will appear and new pests migrate to previously unaffected wine-growing regions, but also because the protocol for dealing with them will be influenced by society and restricted by governmental regulations. Whether that will allow the flexibility that Buckland plans for when designing vineyard remains and unanswered question.
Buckland sees more vineyards moving to coastal regions — not necessarily because of climate change but because they make wine of better quality. That quality-driven shift could help offset some of the impact of climate change, though, because it’s predicted that the increase in temperature will be less in coastal than in inland regions.
In the end, Buckland says “wine style is a huge buffer” to the question of climate change affecting wine. “You can grow Cabernet Sauvignon in the Willamette Valley. You can grow Cabernet Sauvignon in Fresno. They will make incredibly different wines if you do nothing to them. There’s a lot of ground between them.
“Adapting is what we do,” Buckland continued. “As farmers, what we do is adapt to every season at hand.”
Climate change and viticulture
by Karl H. Kazaks