DOES A WARMING CLIMATE MEAN BETTER WINE? (Part One)

Roger C. Bohmrich, Master of Wine

July 30, 2021

Wine is on the front lines of climate change. The many issues and threats presented by rising temperatures and unpredictable, destructive weather are more often feared than cheered. Is it nonetheless possible that the altered climatic patterns which took hold in the second half of the 20th century could actually have given us better wine? Just as climate was becoming a topic of conversation, Wine Spectator released an article in 2003 asking: “Could global warming be good for wine?” Based on vintage and wine ratings, it is not a stretch to conclude that some wines have indeed been the beneficiary of warmer, drier conditions over the past several decades.

            What constitutes a “better” wine, and how is climate implicated? It comes down to ripening: wine quality is associated with optimal maturity of the grapes. This applies to sugar, acids and polyphenols.  For reds, the optimum would mean finer-grained tannins, greater richness and dimension of flavor without sacrificing aromatic expression, all while avoiding the heat of excessive alcohol. A climate-improved red would need to retain a degree of freshness and be free of cooked or overripe flavors. A better white, it could be argued, would possess heightened aromatic intensity along with more weight and flesh while retaining sufficient acidity to offset its generosity. Accordingly, a warming climate which fosters ripening tends to favor red, not white wine. It is probably not off the mark to say that plush, supple reds find more favor than flabby, overblown whites.

The phenology or growth cycle of the grapevine is particularly sensitive to growing season temperatures. A number of varieties have comparatively narrow ranges of tolerance. Pinot Noir is a notable example, preferring an average temperature from 14° C to 16° C (57 ° to 61° F) according to widely cited work by climatologist Gregory V. Jones (Jones et al., 2005). Cabernet Sauvignon, by contrast, is said to do well from 16° C to 19°C (61° F to 66° F). Below a certain minimum, the fruit fails to ripen satisfactorily. At higher levels, berry sugar escalates, acidities drop and juice pH is altered.  Aroma, flavor and phenolic compounds may also be negatively affected if heat intensifies (Zoecklein, 2018).

The range of temperature tolerated by a grape variety represents essential information for growers. Researchers admit, however, that it is difficult to establish the exact upper limit a variety will tolerate. Temperatures in some regions are already pushing beyond the theoretical limits. From 1950 to 1999, growing-season temperatures in the world’s principal wine regions increased by 1.26 ° C (2.27° F) according to a benchmark report of Gregory V. Jones (Jones et al., 2005). He and his co-authors recognized that, during that half-century, improvements in viticulture and winemaking also played a part in boosting wine quality.

Considering technical advances, it would be logical that human actions have contributed to better wine, but how much? Jones calculated that from 10% to 60% of higher vintage ratings were linked to higher growing season temperatures in the 1950-1999 period. His fundamental observation was that “the observed warming of the late 20th century appears to have been mostly beneficial for high-quality wine production worldwide” (Jones et al., 2005). He tracked ratings for several regions, among them Bordeaux and California (Fig. 1), for the vintages from the early 1960s to 2000. The solid trend lines reveal that mean scores improved meaningfully for Bordeaux whereas the gains were comparatively small for California.

Figure 1. Vintage ratings for red wines from the Médoc and Graves regions of Bordeaux (top) and red wines from California (bottom) as analyzed by Jones et al. (2005). The ratings are from Sotheby’s (Stevenson, 2001) and are based on a 0-100 scale. A LOWESS filter is applied to indicate the underlying pattern in the ratings. (Jones, 2003)

Another study of California wines (Alston et al., 2011) examined the causes of increasing Brix levels since 1980. The index the researchers formulated to assess heat did not account for “much” of that rise in the years from 1990 to 2008. Alston concluded that the upswing was the “unintended consequence of wineries responding to market demand and seeking riper flavored, more-intense wines through longer hang times.” Leaving grapes on the vine longer can (within limits) increase sugars, thereby creating richer, more generous wines of higher alcohol content. [See this author’s earlier essay entitled A Question of Ripeness for a discussion of this question.]

How could this hypothesis be tested? One way, admittedly imperfect, is to consider vintage ratings over recent decades for North Coast Cabernet Sauvignon and compare those scores to Degrees Brix for Napa County (see Side Bar and Table at end of article). In this example, do scores move up and down in tandem with Degrees Brix?

Wine Advocate scores for Cabernet average 85.5 points for vintages 1980 to 1989, breaking past 90 points only once (in 1984). In the 1980s, Brix averaged 22.7°, equating to potential alcohol of 12.5%.

The decade of the 1990s shows significantly higher scoring, averaging 91.7. In this decade, sugar ripeness moved up by one degree to 23.7° Brix, resulting in an average alcohol of 13.0%.

In the ten years from 2000 to 2009, only once were any of the vintages rated below 91 points. Brix levels again ticked up, to 25.2° or 13.9% potential alcohol.

In these three decades, ratings and Brix both increased, supporting the argument that greater ripeness, up to a point, does indeed translate to greater critical praise. If we look at individual years, on the other hand, it does not take a statistician to see that the relationship between average degrees Brix and vintage scores is muddied to say the least. There are obvious anomalies which tend to chip away at simplistic conclusions.

These numbers bring us back to the central question. Were higher sugars in California in these decades the result of a changing climate or human mediation? Frankly, this has become largely academic as circumstances have overtaken the findings of the 2011 study. With hindsight, we can say the climatic trend is unambiguous. The graphic below (Fig. 2) lays out the reality of rising temperatures in California, where 15 of the last 20 growing seasons have been 3° to 5° F higher than the 1895-2017 average, with further increases of 4° to 5° F forecasted by the mid-21st century. 

Figure 2. Historic and projected growing season temperatures in California. The shaded green time period contains the notation “15 of the last 20 years.” (Brooks, 2019)

While rising temperatures are hardly advantageous in already-hot regions, warming may have helped locales where grapes did not ripen dependably every year. Surprisingly, these areas include some whose wines are among the most coveted and expensive in the world such as Bordeaux, Burgundy and Piedmont. Their reputations were made by relatively few fabled vintages, perhaps two or three each decade. Devotees of course do not focus on numerous disappointing vintages in their long histories when grapes, particularly for red wines, were harvested well short of full maturity. This is now a worry of the past, except occasionally.

The Loire Valley, long considered cool and marginal, has seen dramatic changes in its weather patterns and as a consequence its best-known red wines, particularly Chinon and Bourgueil, have lost the “greenness” common in earlier times and have gained in richness and suppleness. The following table (Fig. 3) shows the substantial recalibration of Cabernet Franc in recent decades, with a boost in sugar and drop in acidity.

Figure 3.  Sugar and titratable acidity content of Cabernet Franc grapes in the period 1970/1981 to 2010. Data from: Neethling E, et al., Change in climate and berry composition for grapevine varieties cultivated in the Loire Valley, Clima. 53: 89–101, 2012, doi: 10.3354/cr01094, June 2019.

Red grapes have consistently been attaining unaccustomed sugar levels and polyphenolic maturities in many European denominations. Similarly, white wine grapes in cooler zones have experienced an analogous boost in sugars together with a drop in acid levels. Red wines have clearly benefitted; the verdict for dry whites and sparkling wines is more complicated. German Riesling, boasting high acidities and low pH, has mostly profited. The vine has coped successfully with dry summers. On the other hand, warm end-of-season weather has been a death knell for Eiswein (in 2020, a single vintner made ice wine). But there is a real plus: “The danger of late-ripening grape varieties not reaching optimal ripeness has long ceased” (www.germanwines.de).

Similarly, dry Chenin Blanc in the Loire – Saumur or Savennières, for example – boasts ampler fruit expressions along with less intensely biting acidity. In the words of Jacky Blot of Domaine de la Taille Aux Loups in Montlouis, “Fifteen years ago, people wanted more ripeness. Because of climate change, ripe is easy now” (Vinous, July 2020). Perhaps too easy for whites whose character – or “typicity,” as the French say – is associated with lean, incisive taste profiles. Historically, hot growing seasons were not the norm in the Loire, though they did occasionally occur, and the heavy, fat whites they produced were seen as unwanted aberrations.

The world-famous white wine of nearby Chablis, just to the north, has evolved in a similar fashion. While some traditionalists bemoan the disappearance of the bone-dry, reticent Chablis of old – a wine which demanded tempering in bottle – contemporary consumers seem to be more comfortable with a much riper rendition which is immediately enjoyable. As celebrated grower Jean-Marie Raveneau recounted to writer Andrew Jefford: “We always used to chase sugar when I was younger. Now we have to look after our acidity” (Jefford, 2012).

Burgundy as a whole is a case in point. In part, this is because Pinot Noir is particularly sensitive to ambient temperatures (whereas its partner, Chardonnay, is more pliant or plastic). Academics examined climatic conditions for vintages from 1354 to 2018 (Labbé et al., 2019). They found that, up to 1987, grapes were harvested on September 28 on average whereas, from 1988 onward, picking began 13 days earlier. Their summary observation is that “outstanding hot and dry years in the past were outliers,” but have become the norm as of “the transition to rapid Global Warming in 1988.” Research by the BIVB (Bourgogne Wine Board) confirms the altered grape composition in the years since 1986, showing that potential alcohol (that is, sugar level) is trending up while acidity is falling (Atkin, 2020). So far, this has translated to more reliable quality across vintages, and many fewer washouts than in years past.

While the climate conversation tends to revolve around temperature, some researchers give greater weight to precipitation. Beginning around 1990, there have been more frequent low rainfall years in Bordeaux as well as more intense periods of drought (Van Leeuwen & Darriet, 2016). This period has witnessed higher evapotranspiration, which is the sum of transpiration by the vine and evaporation from the soil. The water balance, the difference between precipitation and evapotranspiration, has dropped.  While white grapes may suffer from water deficit, it can be a plus for red varieties: “The best vintages in Bordeaux (where vines are not irrigated) are dry vintages. The frequency of dry vintages has increased over the past three decades and this resulted in better vintage ratings in recent years” (Van Leeuwen et al., 2019). Stated differently, vintage quality correlates more closely with water availability than seasonal temperatures. Academic researcher Cornelis Van Leeuwen points to what he describes as “cool” vintages which are nonetheless of very good to excellent quality: 1985, 1988, 1998, 2001, 2008 and 2010 (Van Leeuwen et al., 2014).

Jones found that, as the growing season temperature reaches a certain threshold, vintage quality is likely to decline. He delineated the relationship of ratings (from Sotheby’s, based on 100 points) to average growing temperatures. As temperatures surpassed an optimum varying by wine type, ratings of critics peaked and declined. This was  found to be a general phenomenon applying, for example, to Médoc and Graves red wines of Bordeaux, Alsace white wines and Loire Valley sweet white wines (Jones, 2003).

In many parts of the world, the stages of the growing season – budbreak, flowering and veraison – have been pushed back. Harvest dates are much earlier – by two to three weeks – in French regions. Despite this, the fruit tends to be consistently richer in sugar. It is clear that the altered phenology of the grapevine is not being dictated by winemakers. We can reasonably conclude from vintage ratings that rising temperatures have had a positive impact on many European cooler-climate wines, reds above all, over recent decades. Mitigation tactics in the vineyard and cellar have undoubtedly played a role in shaping wine outcomes – often for the better – but climate has had the upper hand in many places. There have always been “great” (ideally ripe) vintages in the history of admired European appellations; they are now far more common. Disagreeably meager, thin vintages are a rarity as grapes mature with greater regularity, every year. This is the good news.

The concern is that gains from a changing climate appear to be approaching their theoretical maxima in various parts of the global vineyard.  Ever-hotter conditions threaten to push vulnerable grape varieties in some regions beyond the sweet spot of balanced ripening. There are as well threats from unexpected frosts, violent storms, wild fires and intense drought. Undeniably, there are perils and hazards ahead if current trends continue, and wine may well be the least of our worries. Taking an optimistic stance, we can anticipate that the world will not lack for good and perhaps even better wines in the near to medium term. What is more, there will be pleasant surprises in store from places where wine grapes once struggled to ripen. 

One approach to address this question is to consider vintage ratings over recent decades for North Coast Cabernet Sauvignon and compare those scores to Degrees Brix for Napa County.

Wine Advocate scores for Cabernet average 85.5 points for vintages 1980 to 1989, breaking past 90 points only once (in 1984). In the 1980s, Brix averaged 22.7°, equating to potential alcohol of 12.5%.

The decade of the 1990s shows significantly higher scoring, averaging 91.7. Only twice, in 1998 and 1999, was the rating in the 80s. Scores of 93 to 95 points were awarded to six vintages. In this decade, sugar ripeness moved up by one degree to 23.7° Brix, resulting in an average alcohol content of 13.0%.

In the ten years from 2000 to 2009, only once were any of the vintages rated below 91 points. 2001 and 2007 were given 96 points and two others, 2002 and 2005, a score of 95. Brix levels again ticked up, to 25.2° or 13.9% potential alcohol.

In these three decades, ratings and Brix both increased.

If we look at individual years, on the other hand, it does not take a statistician to see that the relationship between average degrees Brix and vintage scores is muddied to say the least. There are obvious anomalies. In the 1980s, Brix levels were 22° to 23°. The ’84 vintage, rated 92, did slightly surpass 23°. Confusingly, 1983, rated 76, was brought in at the same sugar, 22.3°, as 1982, scored 86. 

In the subsequent decades, 1998 was relatively low scoring (85) yet attained higher sugars (24.1°) than 1994 (95) and 1995 (94), with Brix of 23.2° and 23.6°, respectively. Perhaps most dramatically, the 78-point 2000 vintage came in at slightly higher Brix (23.9°) than the high-flying ’94 and ’95. Finally, it is true that a few of the most recent vintages of North Coast Cabernet (2013, 2015 and 2016) combine elevated Brix of 25° to 26° with spectacular ratings of 97 to 98 points. But then, if Brix tells us why, how could 2017 earn a grade of merely 86 when the sugar (25.2°) is line with 2012, rated 96?

REFERENCES

Alston, JM et al. (2011), Too Much of a Good Thing? Causes and Consequences of Increases in Sugar Content of California Wine Grapes, Journal of Wine Economics, Volume 6, Number 2, Pages 135–159.

 

Atkin, T (Feb 14, 2020), Climate change in Burgundy: Slowing the impact, Decanter.

 

Brooks, L (Jan 2019), Climatologists Say Cabernet’s Days as King in Napa are Numbered, Wine Business Monthly.

 

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https://www.germanwines.de/knowledge/viticulture-winemaking/climate-weather/, accessed May 2021.

 

Jefford, A (Aug 24, 2012), A warm glow for Chablis, FT Magazine, www.ft.com.

 

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Paper 4 from the “Terroir, Geology and Wine: A Tribute to Simon J. Haynes” session held at the Geological Society of America Annual Meeting, Seattle, Washington.

 

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Labbé, T; Pfister, C; Brönnimann, S; Rousseau, D; Franke, J; Bois, B (11 Jan 2019), The longest homogeneous series of grape harvest dates, Beaune 1354-2018, and its significance for the understanding of past and present climate, Climate of the Past | Discussions, https://doi.org/10.5194/cp-2018-179, c Author(s) 2019. CC BY 4.0 License.

 

Robinson, J (March 13, 2015), Climate change and the rise in wine’s alcohol levels, Financial Times, www.ft.com.

 

USDA  California Grape Crush Report, https://www.nass.usda.gov/Statistics_by_State/California/Publications/Specialty_and_Other_Releases/Grapes/Crush/Reports/index.php.

 

Van Leeuwen, C; Blois, B; Séguin, G (2014), Bordeaux et son terroir, Féret, Chapitre 1, p 33.

 

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Wine Quality, Journal of Wine Economics, Volume 11, Number 1, Pages 150–167,

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Van Leeuwen, C et al. (Sep 5, 2019), An Update on the Impact of Climate Change in Viticulture and Potential Adaptations, www.mdpi.com/journal/agronomy.

 

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Wine Advocate, Vintage Chart 1970-2019, www.robertparker.com, last accessed August 2020.

 

Wine Spectator (Nov 14, 2003), Could Global Warming Be Good for Wine? New Study Becomes Hot Topic Among Producers.

 

Wine Spectator, Vintage Chart California/Cabernet/Napa, www.winespectator.com, last accessed August 2020.