Terroir and global warming

When I first started to learn about wine, many French wines commanded a price premium, and were apparently intended as an aspirational connoisseur drink. This, at least, was the idea presented by the (mostly British) commentators of the time. New World wine was seen as much more down-market, as it was not quite so much tied up with the notion of "terroir".

Terroir is a complex issue, and it has thus been the mainstay of wine writers for many decades. The experts obviously understand terroir, and the rest of us apparently do not (at least, until we have read their words on the subject).* Like many people, I suspect that this idea is becoming more and more problematic this century. Shouldn't global climate change be changing the terroir expressed by each grape-growing location? That is, the unique terroir being expressed by any given wine must now be quite different to what was happening (say) 30 years ago.

For example, it has always seemed to me that the main difference between the Cabernet-based wines of Bordeaux, and those elsewhere in the world, has been that most wine-makers try to get their grapes fully ripe each year, while in Bordeaux they got them as ripe as the weather would allow in that year. That is, Bordeaux has traditionally been a marginal climate for Cabernet grapes. As Anne Krebiehl put it (The differences between high- and low-elevation wine):

Médoc, also known as the Left Bank of Bordeaux, is one of the lowest-lying wine regions in the world. This enabled grapes like Cabernet Sauvignon and Merlot to ripen in a marginal climate for these varieties before climate change.

Those last three words are the key to this blog post. If climate change has resulted in warmer temperatures, as we are continually being told (and as seems very obvious, anyway), then Bordeaux should no longer be a marginal Cabernet-ripening  region. It might now be warm enough to be a very consistent growing region; and I thought that we might be able to investigate this idea with some data.

Temperature

We should start by looking at the data on global warming. One good source of data is the National Aeronautics and Space Administration, who have a web page on Global Climate Change. NASA uses their satellites to collect all sorts of data about our planet; and the data of interest here refer to what they call their Global Land-Ocean Temperature Index.

I have produced a graph of their published data below (sourced via Statista). The data illustrate the global average land and ocean surface temperature in °C for the years 1880 to 2020. The numbers are presented relative to a baseline temperature, for the years 1951-1980 — that is, they show how much warmer or colder the world is than it was between 1950 and 1980.

The black line represents the temperature, while the pink line is a 15-year running average (ie. the average of the 15 years centered on that point). The dashed line is simply the 0°C (1951-1980) baseline.

The obvious thing to note is that it was colder before 1940 and warmer after 1970. However, we can go further than this. For example, there has been a steady increase in temperature since 1910, with relative stability for the 30 years before that.** Second, there was a big increase between 1939 and 1945 — this shows you what detonating a lot of bombs will do to you even if you are not at the site of the explosion.

However, for our purposes here, the most important point is that there has been a rapid and continual rise in temperature since c. 1977. I was studying environmental science at university at that time, and no-one mentioned global warming. You can see why; and also why it has become a big issue since then.

Vintage scores

Now we can look at some vintage data for the Bordeaux wine region, covering roughly the same time period. I have already presented these vintage-quality data, in a different context, in a previous post: A century of French wine vintages.

The data used here cover the years 1900 to 2019, for the red, white and dessert wines of Bordeaux. The data come from vintage charts produced by the Cavus Vinifera website (Les millésimes en France de 1899 a nos jours), with a quality score out of 20 for each wine type. I have simply averaged the scores across the three charts, for each year.

The next graph shows the vintage scores (vertically) for each year (horizontally). The black points represent the annual data, while the pink line is the 15-year running average (as in the previous graph). The dashed line simply represents the average score across the whole period.

Clearly, as is true for the temperature, the vintages were below average until 1940, and then above average after 1975. There have been no bad vintages since 1993, so that vintage quality is now consistent from year to year (as predicted). However, unlike the temperature, the rapid increase after 1970 lasted only until the mid-1980s, and the scores have remained roughly steady since then (rather than continuing to increase). So, the continued increase in temperature has not helped the Bordeaux vintages during the past 30 years. Perhaps Bordeaux has now already reached its maximum maturation potential?

Looking briefly at the other French wine regions for which there are similar data (Burgundy, Rhone, Alsace, Loire, Champagne, Beaujolais), there has not been a bad vintage since the end of the 1960s, or even a mediocre vintage since the early 1990s, across all of the wine regions. So, our Bordeaux pattern seems quite general — vintage quality in France is far more consistent now than it was before the temperature increase late last century.

Afterword

It would, of course, be very naive to assume that all there is to global climate change is increased temperature. Indeed, our weather systems have become more erratic ("volatile" is the official term), with increased variation particularly in various forms of precipitation — sometimes the rainfall is too much and sometimes too little in Australia and the USA, for example, and hail has become a problem in parts of Europe.

Indeed, Bordeaux is one of the areas affected by increased hail damage, destroying up to 50% of the crop in the past couple of years. The vignerons are fighting back, as best they can (On a balloon and a prayer: Bordeaux grapples with climate change); but it would be a better idea to actually stop the climate change, if we can.

---

* Compare: Terroir and other myths of winegrowing, with Irrefutable proof through detailed chemical analysis that terroir exists.

** Current estimates suggest that this long-term temperature stability goes all the way back to the mid 1400s — i.e. 400 years (see: Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia).