Now, even the grapes are talking, and new research makes it easy to view the rising thermometer through a rosé-colored glass.
Wine grapes are very sensitive to their climate. Vintners historically produce top wines when an early wet season soaks the plants and a drought succeeds it, allowing the fruit to ripen. Two scientists affiliated with NASA, Columbia's Earth sciences center, and Harvard have assembled records of grape harvests for the past 400 years to show trends produced by changes in temperature and precipitation.
The research, published today in Nature Climate Change, concludes that warming since about 1980 has changed the way wine grapes grow. They no longer need to rely on late-season heat and drought, because temperatures are pumped up already. This chart from the paper shows the departure from average, toward early harvests, since 1980. The scientists looked at historical documents, tree-ring studies of temperature, precipitation, and soil moisture:
The good news is that there's probably been a net increase in wine quality. The bad news: It's not likely to last as warming continues.
Europe received a taste of its hotter future in 2003, when an August heat wave, unprecedented in some 500 years, killed at least 20,000 people. If the extreme heat was a net benefit for vintners, it didn't show up in bottles.
"There may be an upper limit" to the heat's positive effect on wines, said Benjamin Cook, the study's lead author. "For example, 2003 was the earliest harvest in our record (about a month early), but quality ratings were middling for this year."
The grape harvest date and summer temperature charts are not exact opposites. The grape-harvest chart, while mostly a function of temperature, also reflects precipitation trends and growing practices. Wetness can slow the harvest, though much more weakly than heat advances it. But comparing the two shows an inverse relationship. Summer temperatures in Europe, pushed up over time by emissions of carbon dioxide, take off at about the same time that grape harvest dates start to peel back.
Watching the world warm through wine production is vital to vintners, their local economies, and wine aficionados. In the scheme of things, it's not the global economy's biggest problem.
The global economy's biggest problem is that humanity is adding carbon dioxide, the most important heat-trapping gas, to the atmosphere faster than at any time since the dinosaurs were wiped out. A study in Nature Geoscience, published simultaneously with the wine study, concludes that carbon is being injected into the atmosphere at rates unseen since a major heating event about 56 million years ago.
There is no analogue to human-made warming, the scientists say. The rate of climate change "is too fast for many species to adapt, which is likely to result in widespread future extinctions in marine and terrestrial environments that will substantially exceed" any episode in the Cenozoic Era, going back 66 million years.
Bad years ahead for Merlot.
(Updates to clarify the causal relationship the scientists found.)