A warmer climate could pose great risk to some viticultural regions, though many grape-growing areas could benefit, says an Oregon research climatologist.

Throughout the ages, climates have changed. The warming trend observed by scientists in the last 50 years indicates that the world’s climate is possibly changing more rapidly than at any time in Earth’s recent climate history.

“Climates vary and change—and always will,” said Dr. Gregory Jones, associate professor of geography at Southern Oregon University in Ashland.

Jones has experience with the wine industry. He is involved with regional and international viticulture and wine-related research projects, including wine grape varietal trials, and gets his hands dirty in his family’s Abacela Vineyards and Winery near Roseburg, Oregon. He is currently involved in a research project with Oregon State University’s Dr. David Sugar, looking at pear bloom dates in Oregon’s Rogue Valley from 1930 to the present.

Climate changes are slow to occur, but even slow changes are of interest to the wine industry because the climate-variety connection is important in producing the best wines possible, he said.

Each wine grape variety has an optimum zone where grapes ripen and mature best. Grapes grown in climates that are too warm can result in fruit with overripe flavors, lower retention of acid, and unbalanced wines, while those grown in a climate that is too cold do not fully ripen fruit and end up with lower sugar levels, unripe flavors, and produce unbalanced wines.

“Ideally, what any grape grower or winemaker wants is to grow a given variety in its most optimum climate, therefore producing the most consistently ripe fruit with balanced flavors,” Jones noted during a presentation made at the annual meeting of the Washington Association of Wine Grape Growers. “We know that climate allows us to produce a given style of wine. Research shows that grapevine climate/maturity groupings can give an indication of the span of potential ripening period for different varieties based on phenology requirements.”

The results show that each grape variety is generally grown in specific regions and narrow climative zones for optimum quality and production, he explained. Cool climate varieties, like Pinot Gris, Gewürztraminer, and Müller-Thurgau do best where the average growing season temperatures are cool and range from 55° to 59°F. Intermediate climate varieties do best in average growing season temperatures that range from 60° to 63°F, while warm climate varieties, such as Syrah, Cabernet Sauvignon, and Sangiovese, perform well in an average growing season temperature zone of 63° to 66°F. Table grapes and raisins prefer hot climate zones of 66° to 75°F.

“These narrow climatic zones for wine grape varieties put them at a greater potential risk from climatic variations and change than many other crops,” he said, adding that researchers have observed a number of effects related to climate.

“Over the past 50 years, most wine regions have seen warmer, longer growing seasons, altered phenological timing, and altered ripening profiles.”

Other observations or potential wine grape effects from climate change include different disease and/or pest timing, altered water requirements, and the need for management adaptations to deal with the changes.

Climate trends

Jones shared data collected from 1948 to 2002 from 46 climate stations representing 11 grape-growing regions in Washington, Oregon, and California. These weather stations collected what is considered “clean” data, as the stations are not located near urban areas. In Washington State, the regions include Puget Sound and the Columbia Valley; Oregon regions are the Columbia Valley, Willamette Valley, Umpqua Valley, and Rogue Valley. California’s wine grape production was split into five regions—North Valley, Foothills, North Coast, Central Coast, and the Central Valley.

Jones analyzed 16 climate parameters important for grapevine growth and wine production, ranging from growing degree-days and average growing season temperatures to date of last spring frost and fall frost to bloom and ripening period precipitation.

Analysis of the climate trends for the last five decades for Puget Sound and eastern Washington show greater heat accumulation (represented by growing degree-days), an increase in the growing season average temperature, an increase in average ripening period temperature, fewer days below freezing in the spring and fall, and earlier spring frosts, but later fall frosts.

Precipitation trends were mixed during the 54-year period, he noted. Also, the frequencies of winter freezes were variable, although winter temperatures were slightly warmer.

Global wine regions show similar trends during 1950 to 2000, with an average of all 27 wine regions Jones studied showing average growing season temperatures warming by 2.3°F and warmer temperatures during the dormant season. “Also, warming trends are more significant and of greater magnitude in the Northern Hemisphere versus the Southern Hemisphere.”

Across the world’s best wine-producing regions, the trends have been favorable to producing better quality wine grapes and reducing the vintage-to-vintage variability that plagues some regions, Jones said. “However, cool climate regions appear to benefit the most as climate warms, allowing them to produce more consistently good wines.”

Future trends

To project what the future holds in terms of climate, he used a climate model developed at the United Kingdom’s Hadley Centre for Climate Prediction and Research known as the HadCM3. The model is a coupled atmosphere-ocean general circulation model.

“All 27 wine regions we studied show significant warming over the next 50 years,” Jones said, “with trends of temperature increases ranging from 0.3° to 1.1°F per decade. The average warming is 3.6°F over the 50-year period, but some regions (Portugal, Spain) are predicted to warm more than others (South Africa). However, even with a warmer climate, extreme freezes and frosts will still be an issue.”

Accompanying the warmer temperatures will be phenological changes to berry development, he predicted. In other research that Jones has done in North America, Europe, and Australia, he has found that bud break is on average 6 days earlier, bloom 11 days earlier, veraison 15 days earlier, and harvest 17 days earlier than it was 50 years ago.

“With the predicted warming in the next fifty years, we should expect a similar amount of phenological change. These changes would accelerate ripening, with grapes likely being harvested earlier in the year when temperatures are warmer, which would decouple flavor development.”

What does the predicted warming trend mean to grape growers in the next 50 years?

Those located in cool climates should benefit more as they will have more variety choices. “But those growing wine grapes in hot regions will have fewer choices and may no longer be able to produce the same wines without changes in production technologies,” Jones said. “For places like Burgundy, France, it puts them outside what is traditionally known as the optimum Pinot Noir ripening climate. For Napa, it could also be a major issue.” Average growing season temperatures in Napa in 50 years are forecast to be 3.1°F warmer than today.


He predicted that in Washington’s Puget Sound region, the warmer temperatures could provide greater ripening potential and increase the number of varieties that can be grown there. But in eastern Washington, a rise of temperatures by 3.3°F “could put the region in a very different ripening mode for many varieties.”

He fears that in 50 years, there could be large areas in the United States too hot to grow grapes. Much of California could be too hot for grapes, as well as parts of eastern Washington.

“In the next 50 years, there could be numerous additional impacts from the climate change,” Jones said. Water availability may be an issue for regions that are dependent on snowpack for irrigation. Additional changes could speed up grapevine phenological timing by an average of three to eight days. There could be an increase in the presence or intensity of grape pests and diseases.

“However, it is very clear that the impacts of climate change will not be uniform across all varieties and regions. Things will be more challenging in already warm climates.”

To prepare for the future, he believes the industry will need to integrate planning and adaptation strategies to adjust to the predicted changes in climate. He encouraged growers to keep their own records on grapevine phenology and temperature; and, especially, plant a small number of warmer climate varieties to watch how they do in a changing climate. Also, the industry should examine how vineyard management might be adjusted to allow the vine to produce in a warmer world.