In a Warming World, Winemakers Search for Cooler Ground

Aided by science honed over the past 150 years, winemakers across Northern California’s famed Sonoma appellations are starting to take climate change more seriously. How they adapt could revolutionize the wine industry in regions across the globe for the next century.

Welcome to Petaluma Gap, California’s newest viticultural area, where cool fog and soft wind define great wine-making.

Chardonnay Harvest in “The Gap” —Nestled in the southern corner of the Sonoma Coast region, winemakers view Petaluma Gap as a sanctuary, where cooler temperatures and steady winds promote sustainable and prosperous wine production. Just next door, in Napa, grapes are ripening weeks ahead of schedule due to rising temperatures, causing alarm throughout the industry. Photo by Frances Rivetti

Petaluma Gap AVA —To set foot here —planted between the San Francisco Bay and the Pacific Ocean, just 25 miles north of the Golden Gate Bridge — is to understand what great wine-making is all about.

It’s here in this hilly terrain, straddling southern Sonoma and Marin counties, where vineyards bear names like “Cloud Landing,” and the motto is “Wind to Wine,” that local winemakers believe they’ve found the ideal balance between cool tempering breezes and warm ripening sunshine.

But the world is changing. The earth is warming. And perfect wine-making conditions — where good soil, moderate rainfall, cooling fog and tranquil summer breezes prevail — are getting harder to find.

Here in Petaluma Gap, designated in early 2018 as a coveted American Viticultural Area (AVA), winemakers have found a cool, windy refuge from the warming temperatures creeping into California’s deep inland valleys. Not only is the area great for grapes like Pinot Noir and Chardonnay, it’s one of the last remaining places where relatively cool conditions prevail. Just over the hill, in Napa Valley, same-day temperatures could be 10 or even 20 degrees warmer.

Blowing Through “The Gap” —The wind literally defines Petaluma Gap AVA. Its location between the Pacific Ocean and San Pablo Bay offers cooling fog in summer, a pattern less common within neighboring AVAs further inland. This helps improve the wine’s body and complexity. The wind also reduces fungus, prevents frost in winter, decreases heat-related stress on vines, and helps reduce the risk of certain plant diseases.

The longer that grapes stay on the vine — before they over-ripen and fill up with sugar, turning them into raisins — the greater their acidity, adding to their body, texture and complexity — the so-called “mouth-feel” of a particular wine, what winemakers call terrior.

Warm (but not too warm) — Cool (but not too cool) — The Secret of Diurnal Shift

The key to success in Petaluma Gap can be summed up by the climate phenomenon of diurnal shift.

Warm Sunny Days — Cool Foggy Nights — Wider variance in daily temperature, the difference between day-time highs and night-time lows, known as diurnal shift, is a key component to greater stability in the era of climate change. Pictured above, Petaluma Gap AVA, with its signature fog and cooling ocean breezes, offers a rare safe haven for winemakers as rising temperatures render neighboring regions less sustainable for wine-making. Photo by Michael Housewright.
Optimizing between climate and wine quality — Too cool and wine becomes more acidic; too hot and wine becomes too sugary with too much alcohol content. California has become famous for consistently delivering great wines in the optimal zone.

Moving North — and Going Higher in Elevation

According to numerous scientific studies, climate change may cause a forced relocation of wine-making from significant parts of California, according to numerous scientific studies. And the move is already underway, as winemakers have begun scouting out burgeoning wine locations further north — in places like Willamette Valley in Oregon and Columbia Valley in Washington.

Experts point to a troubling bottom line: rising temperatures may soon make it simply too hot to grow certain grapes in many parts of California, where wine-making has enjoyed an illustrious history for 150 years, a history that is the oldest, largest and most renowned in North America.

California Exodus — Rising temperatures from climate change will likely shrink premium wine growing areas throughout California in coming decades, particularly in regions like Napa Valley, parts of northern Sonoma county and Santa Barbara County. A move northward, to cooler areas in Oregon, Washington and even southern British Columbia, could offer winemakers more land. Names like Willamette Valley and Columbia Valley could someday become as famous as Napa Valley is today. Maps by Gregory V. Jones, geographer at Southern Oregon University

Signature locations like Napa Valley may become too hot for premium wine grape varieties like Cabernet Sauvignon. According to a study by Sonoma State University which aggregated data on climate change and its impact on the wine industry worldwide, California may lose nearly 50 percent of current acreage for premium grape growing within the next 50 years.

High Altitude Wine — While most of California’s historic wine regions are located near sea level and closer to coastlines, climate change has spawned a more urgent search for higher elevation, like those in the Sierra Foothills, shown above. Higher altitude offers a number of advantages: cooler summer temperatures, fewer pests, and rocky soils that are better suited for drainage. At higher elevations, grapes receive higher doses of UV light, and this helps them develop thicker skins which can add to the wine’s taste, complexity and texture. These thicker-skinned wines have also proven to be more drought tolerant.

Facing a Host of Problems All At Once

Scientists increasingly point to climate change as the root cause of a number of other serious problems facing winemakers throughout California.

Drought and strains on water supply for irrigation have raised concern as winemakers rely more on misting to cool down grapes when temperatures soar during hot summer days.

Fire Fueled by Climate Change — Local firefighters say greater flame intensity, more arid terrain, hotter, drier winds and longer fire seasons characterize a “new normal” for Northern California’s Wine Country. Photo of the Atlas Fire in Napa County in 2017 by ZUMA Press, Inc. / Alamy

Fires have increased throughout California, as some of the state’s largest and deadliest in history have occurred in the past five years — and their scale and intensity are tied to climate change.

Smoke and particulate matter from fires can drift in the air and taint wine that’s still in the harvest stage situated miles from the fire, and winemakers have yet to figure out solutions to such conditions.

Vines can become stressed during prolonged periods of high temperatures, exposing grapes to more pests and disease. In Southern California, the recent reappearance of the glassy-winged sharpshooter, a notorious vine pest which can spread Pierce’s Disease which is deadly to vines, is linked to the more extreme temperatures produced by climate change, according to UN climatologists.

Beyond warmer temperatures, California has experienced more weather extremes, including less predictable rainfall patterns (too much rain just before wine harvest can devastate crops), floods and more frequent winter frosts — all of which can spell disaster for wine grapes.

Restoring Diversity to California’s Wine Varieties

Climate change is forcing winemakers to get creative.

And winemakers have teamed up with plant biologists and climatologists in their search for innovative solutions.

There are over 1,000 varieties of wine grapes —yet commercial production, dictated by economics, marketing and finicky consumers, narrows that number to fewer than a dozen recognizable names: Cabernet Sauvignon, Merlot, Pinot Noir, Chardonnay, and Sauvignon Blanc make up the bulk of production in California.

The demands of a warming climate will mean winemakers must induce new, more heat-resistant and drought-tolerate grape varieties, and they’ve begun to think outside the box beyond current, long-established consumer preferences.

Thinking beyond tradition — In a world of rising temperatures, more severe droughts, pests and new diseases, winemakers are being pressed to think beyond the most common wine varietals among consumers. In a warming world, heat-tolerant varietals like Grenache, Carignane, and Nebbiolo may become new favorites among consumers who have long preferred wine with more familiar names like Cabernet Sauvignon and Merlot.

Long-forgotten Grapes Make a Comeback

Winemaking has long been about experimentation. For centuries, winemakers have relied on trial and error to find the right kind of grape for the right kind of climate to produce just the right kind of wine.

But factors like rising temperatures from climate change, worsening conditions for droughts, and pests and new disease are pushing winemakers to look backwards.

Re-Diversifying Wine Grape Varieties — Responding to rising temperatures from climate change, winemakers around the world are starting to experiment with less recognizable varieties like the Touriga Nacional Noir grapes shown above, common in Portugal as a Port varietal, yet now being cultivated in the Bordeaux region of France. Many such varieties enjoyed more popularity long ago. Winemakers believe consumers will adapt and come to enjoy wine from these less familiar grapes, in the same manner we prefer Cabernet Sauvignon and Pinot Noir today.

Prunelard Noir is one such variety. Originally cultivated centuries ago in the Gaillac region in southern France, Prunelard Noir is the grandparent grape to Malbec, a heat-tolerant variety that has become more popular in recent years, thanks to winemakers in Argentina and elsewhere. The vine was long thought to have gone extinct after the devastating phylloxera disease that nearly wiped out the wine industry in France during the 19th Century, known as the Great French Wine Blight. Over 100 years later, a chance discovery of an old vine in southern France, a turned out to be a descendant of Prunelard Noir.

Anticipating climate change, Bordeaux winemakers have experienced success with Prunelard Noir as a heat-resistant variety, and a wider reintroduction campaign may soon be underway here in California.

The search for heat-tolerant wine grapes is a global one. In addition to ancient varietals like Prunelard Noir, scientists are experimenting with others from hotter climates like Portugal, Sicily, Spain, Cyprus, and even Mexico and North Africa.

Sustainable Wines —An Ecological Answer to Climate Change

When it comes to wine, consumers play a leading role in making choices about environmental sustainability. From the carbon footprint of the vineyard, to environmental considerations around the production of glass bottles, to the ink used on labels or the use of plastics, to sustainable water use, to the use of pesticides and herbicides, consumers are getting more concerned — and more demanding.

Increasingly, they are asking more questions and making purchasing decisions based on the wine’s climate-friendly profile.

History Reveals Winemakers’ Role in Climate Science

Historians help us understand how people have been making wine for as long as human civilization itself. Archaeologists recently found the oldest evidence of winemaking — an earthenware jar in the Republic of Georgia in the Caucasus region of Eurasia that contained residue of wine, which dates winemaking to as far back as 8,000 years ago.

This means that winemakers have been minding the climate for eight millennia —keeping track of the weather, cultivating vines, experimenting with grape varieties, judging the most suitable areas for growing — for as long as humans have been tilling the soil, for as long as human civilization itself.

Arguably, wine cultivating is near the top of the list of humanity’s achievements: discovering fire, harnessing the wheel, cultivating agriculture, and making wine — arguably, that’s the order of human history.

You could say that winemakers are the oldest climate change scientists in the world.

Winemakers in Petaluma Gap, and throughout the world, will continue to adapt as our climate changes. We may even learn from these winemakers to help us understand climate change science itself.

Ancient Evidence at the Bottom of the Sea — These amphora (shown above), dating from the time of the Roman Empire, were recently discovered by underwater archaeologists from a shipwreck near Kefalonia, an Ionian island off the west coast of Greece. These ceramic containers were a typical method of transporting wine, olive oil, nuts, wheat, barley and other preserved food stuffs throughout the ancient world. They date to between 100 B.C.E. and 100 AD.

Resources, References and Getting out to Petaluma AVA

California Wine Industry — Petaluma Gap AVA — Wine Climate Change

“The End of Cabernet in Napa Valley?,” by Esther Mobley, San Francisco Chronicle, August 16, 2019

“ Climate change isn’t coming for Napa. It’s here, explains S. Kaan Kurtural, UC Davis professor of viticulture and enology.”

“Napa already has moved into another climate category,” Kurtural says. By “climate category,” he’s referring to the Winkler Index, a Davis-developed scale that maps which types of grape varieties can grow within specific temperature bands.

“Cabernet Sauvignon can grow successfully in the Winkler Index’s Regions II, III and IV — but Region V would be pushing it. In 1944, when the system was developed, it put most parts of Napa Valley on the cool side of a Region II; now, most parts are a warm Region III or even a Region IV.”

Resisting Heat — Hot-Friendly Wine Grape Varieties to watch (source: Esther Mobley, San Francisco Chronicle:

Touriga Nacional: Primarily used for Port, this dark, tannic grape variety is becoming popular for table wines in Portugal. Can produce juicy, concentrated, floral wines and is permitted for use in Bordeaux wines.

Tempranillo: Spain’s best-known red grape, which typically forms the basis for Rioja wines, is known for its ability to age beautifully. Fruity and easy-drinking while young, it can take on leather and tobacco flavors in maturity.

Alicante Bouschet: This Portuguese variety has a long history in California; many 19th century vineyards included it. Most important, the grape is a teinturier, a rare class of wine grapes whose flesh is red, rather than clear, which helps contribute color to wines.

Tannat: Its roots are in southern France, but Tannat has now become the calling card for Uruguay’s wine industry, which prizes the thick-skinned grape for its drought and heat tolerance. Can retain lots of structure and freshness late into the growing season.

Alvarinho/Albariño: Whether it goes by its Portuguese or Spanish moniker, this white grape can produce crisp, high-acid wines in warm climates. It was one of the three white grape varieties recently permitted for use in Bordeaux wines.

“Could Climate Change Mean an End to Cabernet in Napa Valley? This Winemaker Thinks So,” by Dana Rebmann, Sonoma Magazine, January 2020

“It’s hard to tell people Cabernet is going to die. It’s hard to say it’s over because it’s still our lifeblood. It’s the beating heart of what we do and we do it really well,” says Petroski. “Some of the best wines in the world are made here in the Napa Valley, so it’s hard to have that conversation. But I think the other side of that conversation is that we’re forward-thinking. We are evaluating, we’re looking to the future.”

“Why You Should Pay Attention to the Winkler Scale,” Dracaena Wines, October 5, 2016

“California has growing regions which lie in all five regions; from Mendocino and Sonoma in the north (which lie in regions I-III) to the San Joaquin Valley and points south, which lie in regions IV and V.”

Scientific Study: Climate Change, Wine and Conservation, Proceedings of the National Academy of Sciences of the United States of America, by Lee Hannah, Patrick R. Roehrdanz, Makihiko Ikegami, Anderson V. Shepard, M. Rebecca Shaw, Gary Tabor, Lu Zhi, Pablo A. Marquet, and Robert J. Hijmans, published April 23, 2013

“Area suitable for viticulture decreases 25% to 73% in major wine producing regions by 2050 in the higher RCP 8.5 concentration pathway and 19% to 62% in the lower RCP 4.5. Climate change may cause establishment of vineyards at higher elevations that will increase impacts on upland ecosystems and may lead to conversion of natural vegetation as production shifts to higher latitudes in areas such as western North America. Attempts to maintain wine grape productivity and quality in the face of warming may be associated with increased water use for irrigation and to cool grapes through misting or sprinkling, creating potential for freshwater conservation impacts. Agricultural adaptation and conservation efforts are needed that anticipate these multiple possible indirect effects.”

Scientific Study: The Impact of Climate Change on the Global Wine Industry: Challenges and Solutions, Wine Economic and Policy, Volume 3, Issue 2, December 2014, by Michelle Renee Mozell and Liz Thach, Sonoma State University

“Region by region, climate change would shift wine production, especially in terms of grape selection. By 2100, it is possible that the United States could lose up to 81% of its premium winegrape acreage (Kay, 2006). In California, warming temperatures and a reduction in fresh water in the next half century may deliver an enormous loss of land suitable for premium grape production, especially in Napa and Santa Barbara Counties where land loss could be near 50% of current acreage (Kirkpatrick, 2011). Another study suggests that these regions would be lost completely finding only the narrow coastal bands and the Sierra Nevada left suitable for production (Kay, 2006).”

“Chateau Al Gore,” by Mike Veseth, The Wine Economist, blog posted dated October 16, 2007

“I don’t know anyone in the wine business who does not take the fact of climate change seriously.”

“The geography of wine in the western U.S. is likely to undergo very significant changes in the coming years. Some areas that are currently in the “hot climate” range, like Lodi California, and currently specialize in hot climate grapes like Zinfandel may become too hot to make quality wines at all. Some “cool climate” Pinot Noir areas, like Santa Barbara and Oregon’s Willamette Valley, may bet too warm for those varietals and the Pinot will have to be replaced with more heat-friendly varietals such as Merlot, Malbec, Syrah or Cab. And some areas that are now considered too cold for quality wine production may become viable.”

“Understanding Wind, an Underappreciated Part of Wine,” by Roger Morris, Wine Enthusiast, May 14, 2020

“One of California’s newest appellations, the Petaluma Gap, became an American Viticultural Area (AVA) in 2017. It’s partly defined by its “wind gap” that channels cold air from the Pacific Ocean into the interior of Sonoma and Marin counties.

“Wind dries things out from the cooling fog, and we need that window of time,” says Ria D’Aversa, farming manager for McEvoy Ranch. It’s especially important to an organic operation like McEvoy, where synthetic sprays can’t be used to kill fungus.”

“The Real Difference Between Cool-Climate and Warm-Climate Wine,” by Lauren Mowery, Wine Enthusiast, May 1, 2018

Diurnal Shift: “The Climate Phenomenon that Produces Wines with ‘Electric Acidity,’ by Kathleen Willcox, Wine Enthusiast, June 6, 2020

“High-Altitude Vineyards that are Changing Wine,” by Sorrel Moseley-Williams, Wine Enthusiast, April 5, 2018

Wine Science And New Varieties of Grape for Climate Change Threat

“Researchers to investigate drought-tolerant vines,” by University of Adelaide Australia, Phys.Org, published July 12, 2019

Wine researchers at the University of Adelaide are investigating drought-tolerant grape varieties from Cyprus for their suitability for Australian conditions.

The Cypriot varieties Xynisteri (white) and Maratheftiko (red) have just been released from Australian quarantine and are being propagated at the University’s Waite campus before being placed in trials, replicating those being undertaken in commercial Cypriot vineyards.

“UC Davis releases 5 new wine grape varieties,” by Amy Quinton, University of California Davis, December 18, 2019

“To create the new varieties, Walker crossed a grapevine species from the southwestern U.S. and northern Mexico, Vitis arizonica, which carries a single dominant gene for resistance to Pierce’s disease and was used to cross back to Vitis vinifera over four to five generations. It’s taken about 20 years to develop the five patent-pending selections that are now being released.”

“Ambulo blanc, one of two new white grape varieties, is similar to sauvignon blanc and has been tested in Sonoma, Temecula and Napa.”

“In Napa Valley, Winemakers Fight Climate Change On All Fronts,” by Eric Asimov, New York Times, October 31, 2019

Scientific Study: Diversity buffers winegrowing regions from climate change losses, Proceedings of the National Academy of Sciences of the United States of America, by Ignacio Morales-Castilla, Iñaki García de Cortázar-Atauri, Benjamin I. Cook, Thierry Lacombe, Amber Parker, Cornelis van Leeuwen, Kimberly A. Nicholas, and Elizabeth M. Wolkovich. Published February 11, 2020

Wine History in an era of 21st Century Climate Change

“Mission Revival: State’s first wine grape, circa 1760, rides again, by Ester Mobley, San Francisco Chronicle, March 23, 2017

“Mission was the first wine grape (vitis vinifera) planted in the United States — in fact, in North America. Brought to Mexico from Spain, where it’s known as Listán Prieto, in 1540, it was planted in New Mexico in the 1620s. The grape was first cultivated in California at the Mission San Diego sometime after Junípero Serra founded it in 1769. Eventually, Mission vineyards grew at all of California’s missions, from 1 acre at Santa Clara to 170 acres at San Gabriel.”

“ ‘World’s Oldest Wine’ found in 8,000 year old jars in Georgia,” BBC News, November 13, 2017

“The earthenware jars containing residual wine compounds were found in two sites south of the Georgian capital, Tbilisi, researchers said.

“Some of the jars bore images of grape clusters and a man dancing.”

Resources on the Petaluma Gap AVA, local winemakers and sustainable winemaking

Petaluma Gap Winegrowers Alliance — provides resources, maps, news, developments and events for winemakers and related vendors in the Petaluma Gap American Viticultural Area (AVA)

“The Women Who Breathe Life Into the Petaluma Gap AVA,” by Michelle Williams, Forbes, July 7, 2020

“How Does Your Love of Wine Contribute to Climate Change?,” by Eric Asimov, New York Times, April 30, 2019

“Consumers are most powerful, in my view, in their role as buyers of products, so they can have an impact if they are able to distinguish between products that are climate-friendly and those that are not,” said Mike Veseth, a retired economics professor who writes the blog The Wine Economist. “The problem is that, unless they do a lot of research, consumers don’t really know the carbon footprint of the wines they purchase and so cannot steer their dollars to those who do best.”

California Sustainable Winegrowing Alliance — a member-driven organization devoted to developing and sharing knowledge about sustainable wine in California

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Science Writing for Humans

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