A tried and true way to bring home the reality of global warming is to focus on its impact on beloved agricultural products, such as Durham wheat (for pasta), cacao (for chocolate), and barley (for beer). Grapes follow in this tradition, with recent articles on how shifts in climate are shifting where wine grapes can grow.
But wine grapes have also been used by climate deniers to argue that humans are not causing global warming. Those arguments are not especially sound, but they fall apart for interesting reasons. The long and short of it is that these vines tell an interesting climate tale.
The premise is that grapes are dependent on a specific temperature range, so that where grapes grow reflects where that temperature range occurs.
And indeed, grape-growing regions are shifting. Traditional areas in Australia, France, and California are running up against the upper temperature limits. In coming decades, if no one does anything about climate change, growers will have to shift to other grape varieties or give up viticulture altogether. In France, shifting to new varieties would be problematic because specific types of wine, and therefore specific varieties of grape, are tied to particular regions by law.
Meanwhile, new wine regions in China and other areas are opening up. Parts of England and Nova Scotia, which have been quietly growing white grapes for years, are starting to grow reds.
Obviously, the possibility of new wine regions means economic opportunity for some. This is not entirely a story of doom and gloom. But creating new vineyards necessarily means destroying something else, because there is no land that isn’t already occupied doing something. In China, for example, planting new vineyards means destroying giant panda habitat. In the United States, it could mean destroying the habitat corridors that the wildlife of our western parks depends on.
It’s also important to recognize that even if total annual wine production does not change much in coming decades, the relocation of wine would hurt a lot of people. Industry tends to relocate much faster than population and culture do–consider the economic blight left behind when manufacturing jobs move overseas. The success of wineries in China and Washington State will be small comfort to the owners of bed-and-breakfasts in Napa Valley, California or the Bordeaux region of France.
But if changing climate drives changes in viticulture, does it follow that historical changes in the wine industry can be used to infer climate?
Researchers have made the attempt, and depending on their study designs it is possible they succeeded. Most likely, historical records of wine production could work to augment other sources of climate data, such as records of blooming and harvest times, records of weather, and studies of tree rings and lake sediments.
But the connection between climate and grape vines is a lot more tenuous than it might at first appear.
Grapes make a poor indicator of temperature because they are also dependent on other factors besides temperature for their growth. Rainfall, for example, is important to grapes. Perhaps more to the point, grapes are dependent on humans wanting to grow grapes.
It is possible to grow grapes in Great Britain, just as it is possible to grow them in Nova Scotia, the Pacific Northwest of the United States, and even Alaska. It’s not that you couldn’t make wine in those places until recently–it’s that you couldn’t make good wine. A certain inertia of reputation is probably in play, too, since the British wine industry has actually been growing in both production and quality since the 1950’s.
The many English vineyards of the early Middle Ages might have been a sign that temperatures were warmer then than in more recent historical periods. Climate deniers sometimes use this as evidence for their cause, the idea being that the Industrial Revolution isn’t a precondition for warm temperatures (although there are more English vineyards now, so if grapes did work as a proxy, they’d be evidence of unprecedented heat).
The problem with this line of reasoning is we don’t know how good the Medieval English wine was. It might have been terrible. At the time, the English used much of their wine for celebrating Mass, so pleasure at table wasn’t the point. Economic changes, such as easier importation of quality French wines and the closing of the English monasteries, probably did more to hurt the English vineyards than the climate did.
In any case, grapes are not a good indicator of climate past, but they are a good indication of climate present. Because the wine industry isn’t indulging in climate denial–when scientists predict where wine grape growing weather is likely to move, they find wine grape growers already there. The vineyards opening in new places or shifting to new varieties are well-aware and willing to admit that the climate is changing.