Winemakers pore over potential effect

A recent story by Esther Mobley in the San Francisco Chronicle titled “The End of Cabernet in the Napa Valley?” outlines what some wineries there are doing now to head off the impacts of climate change.

Some of the feared changes could be conditions untenable for growing Cabernet Sauvignon as it’s grown today, which in turn could end the grape’s reign as the “lifeblood of Napa Valley,” according to Mobley.

As Mobley wrote, not only is Cabernet Sauvignon America’s favorite wine, it also accounts for 65% of the grapevines grown in Napa.

Several bunches of Riesling grapes edge toward maturity in a vineyard on Orchard Mesa. These and other grapes around the Grand Valley are a week or so behind schedule after a cool spring delayed development.
Several bunches of Riesling grapes edge toward maturity in a vineyard on Orchard Mesa. These and other grapes around the Grand Valley are a week or so behind schedule after a cool spring delayed development.

In 2018, Mobley reported, the crop reached a record $1 billion in gross value.

But the industry already is feeling some effects of warming temperatures and a handful of Napa Valley winemakers, concerned that within the next 30–50 years the region may be too warm for Cabernet Sauvignon, are planting experimental vineyards with warm-weather grape varieties from Italy, Spain and Portugal.

“I hear some wineries saying, ‘We’re going to have to start thinking about different grape varieties in 30 years,’ ” winemaker Dan Petroski from Larkmead Vineyards told Mobley, who responded, “You’re going to start thinking about it in 30 years?”

Halfway around the world, in Bordeaux, warmer temperatures and longer growing seasons already have brought earlier harvests and complaints about overripe grapes.

In a country where winemaking is monitored from vine to glass, growers have been given the go-ahead for seven new varieties as a hedge against climate change and erratic growing conditions just in case Merlot loses its characteristic style.

High temperatures can cause grapes to ripen beyond what has been traditional and produce too much sugar, which leads to a higher alcohol content and a completely different, and not always desired, flavor profile.

The connection these disparate areas have with the Grand Valley is complex and not unrelated.

Global climate change isn’t limited to warming temperatures, although that factor is of no little concern. There is a wide array of connected challenges keeping fruit producers awake at night, including more wildfires, the spread of new pests and diseases, drought and capricious weather events (including seasonal changes in where and how precipitation falls).

Phylloxera, that microscopic, aphid-like insect that drains the nutrients from grape roots, is spreading across the Grand Valley. Perhaps it’s always been here, but its spread likely is aided by the absence of a deep killing cold winter, the same sort of winters that in the past protected the West’s spruce/fir forests from the spruce bud worm.

Other changes, in some cases a longer growing season and in others erratic weather events such as unexpected lower temperatures, are all part of the puzzle of climate change.

Although there are signs the growing season in western Colorado in recent years has lengthened by a week or so, state viticulturist Horst Caspari at the CSU Research Station on Orchard Mesa said the average temperature this past May was 56.7 degrees, the lowest in 45 years, and more than 10 degrees colder than the 66.1 average of May 2018.

“We fell behind by 153 growing days,” Caspari said. “That’s almost half a month (of plant development) we didn’t get.”

That is why grape or peach growers in the valley will tell you their crops this year are a week to 10 days behind.

Some growers, such as Kaibab Sauvage of Colorado Vineyard Specialists in Palisade, already are experimenting with some lesser-known varieties, testing their adaptability to western Colorado along with their acceptance by winemakers.

He suggested a bit of warming may be welcome.

“If our winters get five degrees warmer, we’ll have a more consistent crop,” Sauvage said earlier this month. “So if we could get rid of our winter lows, we may have a longer ripening season.”

Warmer air also holds more moisture, but five degrees warmer could make the difference between precipitation falling as rain, which quickly runs off, or snow, and Colorado’s agriculture is largely dependent on a deep snowpack for summer irrigation.

Grapevines start their growing season when the daily temperature reaches 50 degrees. Above 50 degrees, growing (or heat) degree days began to accumulate. The number of growing degree days is equal to the number of degrees Fahrenheit over 50 degrees, based on average daily temperature.

Grape growers monitor these growing degree days (and other climate-connected factors) to predict bloom, veraison and maturity.

A hot July and August helped make up an early shortfall in growing degree days caused by that cool May.

“Earlier we were 12 days behind last year, and now we’re about six days behind,” Sauvage said.

High temperatures help growing degree days accumulate, Caspari said.

“We can accumulate a lot of heat when we see 99 and 100 degrees, which we have recently,” Caspari said. “It might take 20–30 days in other months to get that same amount.”

But too much heat causes uneven ripening and when the thermometer hits triple digits, most plants go into a heat- induced dormancy, waiting out the blast furnace of August.

Caspari said nine of the 10 warmest years in nearly 45 years of record-keeping at the research station have come since 2000.

Rising temperatures may prove favorable to grape varieties that can take a lot of heat without getting too ripe, as well as lead to vineyards showing up in northern countries.

Plus, a longer growing season will benefit high-elevation vineyards such as those near Paonia.

“It seems like the whole spring season has shifted,” said Aldis Stratins of the National Weather Service’s Grand Junction office. “In some cases it was a few weeks and at one (weather) site it was up to a month.”

He said June also was 1–3 degrees below normal at various weather sites across the region.

“So you’re still below average,” he said. “So then you have to ask, do we really have a ‘normal’? We live in an area with a lot of variability and while we’re seeing some changes, I’m not sure I would jump on anything quite yet.”

“You need to take a long view of climate,” Stratins said. “You can pick numbers and years, but you need to look at 20, 30 and more years to see what’s actually happening.”