If you won’t believe a climate scientist when they tell you recent summers have been abnormally hot, how about a vintner? In vino veritas, after all (in wine lies the truth). Newly published records of 6.5 centuries of grape harvests reveal recent changes to Western Europe’s climate are like nothing we have seen before.
Even by French standards, the inhabitants of Burgundy take their wine seriously. So seriously that for 664 years they have been recording the timing of their annual harvest, either directly, or in records of payments to grape pickers and council reports.
Dr Thomas Labbé of the University of Burgundy dug his way through numerous archives to discover the dates at which the harvest around Beaune began. He’s now published the longest record of harvest dates ever released, beginning in 1354, when the 100 Years War, if it was a person, wouldn’t have been old enough to drink.
After hot, dry summers grapes are picked earlier than they are after cooler, wetter ones, something Labbé confirmed by comparing the harvest dates with local temperature records in the years since they became available.
"The record is clearly divided in two parts," Labbé said in a statement. For more than 600 years average harvest date was September 28 – early ones were the exception. Since 1988 the average date has shifted to September 15, indicating much hotter conditions.
"We did not anticipate that the accelerated warming trend since the mid-1980s would stand out so clearly in the series," said Professor Christian Pfister of the University of Bern, who co-authored an analysis of Labbé’s data in Climate of the Past. "The transition to a rapid global warming period after 1988 stands out very clearly. The exceptional character of the last 30 years becomes apparent to everybody."
Climate scientists frequently warn against taking a single location as indicative of the entire globe. There can be a variety of reasons why a local area is out of step with wider trends. However, the evidence Labbé assembled tallies quite well with another long-term record from an activity of immense cultural significance: the timing of the Japanese cherry blossom festivals, for which we have an even longer, although less complete, record.
Wine harvests indicate temperature from April to July. Cherry blossoms tell a tale of spring. Records of the freezing of a Japanese lake and the thawing of a Scandinavian river show the winters in those regions have recently become similarly out of step with previous centuries.
Far longer-term climatic records can be tracked from tree rings, ice cores, or stalagmites, among other sources, but these indirect measures are less precise than the harvest data Labbé has collected.