Wine Trends that Matter - Climate Change

by Fred Swan - Guest Blogger

In a new series of articles, I’ll be highlighting several important, ongoing trends related to wine. I’ll tell you how each affects avid wine consumers personally. Today’s article addresses climate change.

Climates are Changing

Climates are changing globally. I say “climates,” rather than “climate,” because there’s not just one climate. There are a great many. And they are all changing right now.

For the moment, let’s not focus on why climates are changing or what might be done about it. And let’s not argue about whether the current changes are directional and long term or just episodes in the earth’s history of rising and lowering temperatures. Let’s just accept that climates are changing.

Climate Changes are Especially Easy to Observe in Wine Regions

Why? Because wine grapes are an annual crop with growing seasons that are very closely observed and accurately recorded. Because individual grape varieties have very specific tendencies and needs with respect to warmth, sunlight, and water availability. Because grape growers are farmers who watch the weather like hawks and whose primary job is making sure there is a successful crop every year. And because we don’t taste vintages in the bread we bake or the steaks we grill, but we do taste them in wines.

Concrete Proof of Changes

Gregory Jones, Ph.D. is the world’s foremost expert on climate with respect to viticulture. Last August, he led a seminar at my WWET conference for professional wine writers in Willamette Valley. He presented clear evidence—based on actual measurements, not models—that climates are changing in wine regions globally.

From 1901 through 2017, all wine regions have seen a significant rise in average daily temperature during the growing season. Of course, there is variation from year to year, up and down. But, the overall trend is clearly up. Perth Australia is up 3.3°F, Napa Valley 3.1°, Burgundy 2.7°, and the previously too-cool-for-wine, southern England, which is now making lovely sparkling wine that is evocative of Champagne, 2.2°. [Let’s ponder that for a moment. The difference between being too cold and making excellent bubbles is a numerically slight temperature bump.]

The rate of temperature increase is also rising. On average, the daily temperature during growing season in cool-climate winegrowing regions around the world has risen 2°F since 1950. In Oregon’s Willamette Valley, 15 of the 20 most recent vintages have been between 2.2 and 3 standard deviations higher than that region’s 123-year mean. In this case, a standard deviation is about 1.8° F. So, these recent vintages have been 4–5.5° warmer. Only three vintages in the past 29 years have been below the mean (1999, 2010, and 2011).

Sunlight and Warmth Affects Ripening and Accumulation of Sugar in Grapes

Any given grape variety requires a certain, aggregate amount of sunlight and warmth during the growing season to achieve palatable ripeness and sufficient sugar content for good wine. There are other variables, but sunlight and heat are the two most important factors. Generally speaking, the more sunlight and heat there are each day during the growing season, the fewer days it takes grapes to achieve the desired levels.

The growing season begins once days get warm enough in the spring, typically a few days with temperatures at or above 50°F, that vines come out of dormancy and their sap begins to flow. The end of the growing season, harvest, comes when sugar concentration is in a range producers are happy with, acidity is well balanced, and flavors (and tannins for red wines) are developed as desired—or when harvest is necessitated by unfavorable weather.

It’s important to know that accumulation of sugar and ripening in terms of flavors and tannins do not necessarily progress at the same rate. There are several reasons for that. Not the least of these is that very hot days cause vines to shut down and can lead to dehydration. That increases sugar concentration but does not contribute to ripening. Flavors and tannins tend to be best when allowed to develop over a long growing season. But, if sugars get very high, harvest becomes necessary even if its early in the season and flavors aren’t fully developed.

Warmth Affects Acidity Levels in Wine Grapes

Grapes contain several different types of acid. Tartaric acid is the most common and tends to remain stable over the growing season. Malic acid is also important in wine grapes, but it’s levels fall as the season progresses.

Grape vines principally fuel their growth and ripening with carbohydrates produced by photosynthesis. The secondary fuel is malic acid. 

Temperature is like a gas pedal for growth and ripening in the vines. The higher the temperature above 50°, the faster vines grow and ripen and the more fuel they consume. When heat during the day pushes fuel consumption above a level photosynthesis alone can support—or at night when there is no photosynthesis at all—the vines consumer malic acid at a higher rate.

In some regions, such as Chablis, less malic acid at harvest may be considered a good thing. However, in a great many, appreciably lower malic acid leads to wines that will feel and taste less fresh in the mouth than we might prefer. 

Every Grape Variety Thrives Only Within a Particular Average Temperature Range

Some varieties have a tight range. Pinot Gris is best between 55°F and 61°. Pinot Noir likes 57–61°. Zinfandel is best at 64-68°. 

Other varieties are more tolerant. Perhaps surprisingly, Riesling is the most forgiving among cherished wine grapes. It’s happy from 55° to about 63.5,° but that’s still just a 8.5° spread.

While varieties have a temperature range for excellence, regions have ranges of typical temperatures. A region which averages 60° will be generally suitable for Pinot Noir. However, most years will actually be either below 60° or above it. With margin of just 1° between average temperature and the limit for best Pinot Noir growing, such a region may often have years which are warmer than ideal for that grape.

Adapting to Warming Climates

The significance of a warming climate to grape growing in a particular region depends on what that climate has traditionally been. If the climate was very cool, as in southern England, the warming may be seen as a positive—at least from a short-term, viticultural perspective. In Champagne, lower acid grapes are leading producers to make adjustments, including decreasing the dosage. In Alsace, which is warmer but still primarily a white wine zone, producers are increasingly faced with the choice between higher residual sugar or higher alcohol.

If, on the other hand, the climate was already quite warm or was already on the margins of being cool enough for grape varieties significant to that region, then the warming will be problematic. Such a region will have more years at, or above, the ideal temperature range.

If the climate was moderate, again, warming may render the region unsuitable for its traditional grape varieties. Such a region may adjust by grafting over to different varieties which will do well in the new climate. However, varieties don’t thrive in a particular area solely due to climate. Soil type, availability of water and other variables are important. So, finding varieties that will excel may be difficult. 

If the climate was already warm or hot, additional warming may require a shift not just in variety, but in style. Port-style, fortified wines may need to supplant dry, full-bodied reds. But, will there be a market for a significant increase in wines of that style? Probably not.

The vines of Toro are kept low and very widely spaced to balance water requirements and availability during the hot, dry summers.

Growers can change their viticultural regimes to somewhat reduce the effect of warming on the grapes. Adjustments could include increasing crop load or allowing more canopy growth, to retard ripening. Changing trellising schemes may help. Increasing irrigation can reduce dehydration. But irrigation isn’t always possible. These approaches may also decrease wine quality or result in a somewhat different character.

Varietal Change

There is only so much growers can do to shepherd vines and their grapes through vintages that are too warm for the variety. Eventually, if warmth continues to increase, different varieties need to be planted or grafted

Such transitions aren’t rapid. It takes at least three for a newly grafted vine to be productive. Newly planted vines take longer. And, for some some wines, there’s another five to ten years before vines reach ideal maturity. It also takes times for local regulations in Europe, which may need to change in order to allow different varieties, to be amended.

All over the winegrowing world, vineyard and winery owners are weighing their options. Some, even in Bordeaux, are planting new varieties on an experimental basis. Famous Left Bank wines of 2040 may include Touriga Nacional.

The sweet, botrytized wines of Bordeaux are made possible by cool, foggy mornings late in the growing season. How will those wines change when the climate is too warm for fog like this?

Other Effects of Warming Climates on the Growing Season, Sugar Accumulation, and Ripening

Warming can have additional ramifications beyond the character, or suitability, of particular varieties. A warming climate can mean vines wake up and start their growing season earlier in the year. In regions with a short growing season, that might mean the season will be a few days longer. That could be good for both sugar accumulation and ripeness. 

In some cases, though, the early warmth doesn’t last. Several warm days will spur vines to action, but those days may be followed by a hard frost. Vines are more vulnerable to frost when their sap is flowing, and even more so later when leaves or flowers have emerged. So, this warm-then-cold scenario can cause serious damage and reduce crop size, quality, or both. This has been an issue for several French growing regions in recent years.

If greater heat results in earlier ripening, that pull harvest into the heart of summer. That, in turn, can result in two things. One is that grapes won’t benefit from an extended and moderate period of ripening at the end of the season, thus reducing the resulting wine’s complexity and balance. It can also mean the grapes will themselves be higher in temperature at harvest. The upshot of that is both lower acidity in the grapes and more electricity required to cool them down when they arrive at the winery.

In regions that were already warm, greater heat will also increase the number of days where peak temperatures are so high that the vines shut down. That is rarely a positive development. In extreme cases, vines may even die. That happened in Australia’s Barossa Valley during the extended heat wave of 2019.

Of course, warming can also exacerbate drought and wildfires. Recently, literally half of Kangaroo Island went up in flames. The wine-producing island, just off the coast of South Australia, saw the exact same territory burn 11 years ago. Then, the fire took eight days to do its damage. This year, fueled by hot air and tinder-dry vegetation, fire consumed the same acreage in just six hours.


Climates are changing all over the world. Specific changes in wine regions are obvious through empirical data and observation. The changes are also manifest in the wines themselves. 

Assuming the direction of change isn’t reversed, regional wine styles to which we are accustomed will be no more. Natural acidity will be lower, alcohol higher, balance will shift more toward fruity (as opposed to savory), and traditional varieties will be abandoned. Everyone who pays attention to the wine they drink will notice the effects of climate change.

Copyright JJ Buckley 2020. Vineyard photos by Fred Swan. All rights reserved.

JJ Buckley guest blogger Fred Swan is a San Francisco-based wine writer, educator, and authority on California wines and wineries. His writing  appears in The Tasting Panel, SOMM Journal,,,, and his own site, FredSwan.Wine (formerly NorCalWine). He teaches at the San Francisco Wine School. He's founder of Wine Writers' Educational Tours, an annual, educational conference for professional wine writers. He also leads private wine tours and conducts tastings and and seminars. Fred’s certifications include WSET Diploma, Certified Sommelier, California Wine Appellation Specialist, Certified Specialist of Wine, French Wine Scholar, Italian Wine Professional, Napa Valley Wine Educator, Northwest Wine Appellation Specialist, and Level 3 WSET Educator. He's been awarded a fellowship by the Symposium for Professional Wine Writers three times.