By Tim Radford
LONDON, 6 September, 2019 − French wines tell a remarkable story: climate scientists and historians, with a new wine list to savour, have carefully reconstructed the harvest dates for Burgundy – one of the most important wine regions of France – to highlight the dramatic change in global climate.
Grapes in Burgundy are now picked 13 days earlier than the average for the last 664 years. And the advance in harvest dates has been dramatic: almost all since 1988.
The finding is based on painstaking study of data going back to 1354. From medieval times Burgundian growers and civic authorities had an unusual communal arrangement: they each year collectively considered the growing conditions and imposed a date before which no grapes might be picked.
And scientists from France, Germany and Switzerland report in the journal Climate of the Past that they worked through all surviving records to provide an accurate record of the harvest date around the city of Beaune.
“The transition to a rapid global warming after 1988 stands out very clearly. We hope people start to realistically consider the climate situation in which the planet is at present”
Since grapes are highly sensitive to temperature and rainfall, and the quality and reputation of Burgundy has been well-established for centuries, the researchers are confident that the data confirm a dramatic warming trend.
Even in a much cooler past, exceptionally early harvests were not unknown. The researchers counted 33 altogether, and 21 of these happened between 1393 and 1719, and five between 1720 and 2002. In the 16 years since 2003, there have been eight outstandingly warm spring-summer seasons, and five of those have happened in the last eight years.
“In sum, the 664-year-long Beaune grape harvest date series demonstrates that outstanding hot and dry years in the past were outliers, while they have become the norm since transition to rapid warming in 1988,” they write.
Historical reconstructions are not easy: data had been assembled before, but these records turned out to be riddled with copying, typing and printing errors. There were administrative changes (after 1906, city authorities in the Burgundian capital of Dijon ceased to set or record a harvest date).
There were accounts kept by the dukes of Burgundy, and records of payments for grapevine labourers maintained by church authorities in Beaune, evidence of purchases of food for the harvesters, and records of sales to the King of France.
But those six centuries were also marked by the Little Ice Age, the Thirty Years War between Catholic and Protestant states from 1618 to 1648, several epidemics of plague, and the arrival of the vineyard-destroying infection phylloxera.
So the researchers had to verify their proxy history of regional climate from tree-ring data, and from vineyard records kept in Switzerland, as well as temperature records from Paris.
The wine industry is vulnerable to climate change: researchers noted three years ago that harvests in Burgundy and in Vaud in Switzerland were up to two weeks earlier and that climate change had begun to warm southern England’s chalky soils to the a degree that made them yield sparkling wines to match qualities pursued in the Champagne region of France.
But the same soaring temperatures that for the moment have helped the grower have begun to impose costs on the grape pickers, who become less productive as the mercury rises.
So the confirmation that harvests are earlier is not in itself news. The data from Beaune and Dijon are best seen as another example of painstaking phenological research. Phenology is the science of when insects hatch, trees bud and birds nest, and in the Burgundian series climate scientists now have a continuous record stretching back 664 years. The story told by the series is unequivocal.
“The transition to a rapid global warming after 1988 stands out very clearly,” said Christian Pfister of the University of Bern in Switzerland, one of the authors.
“The exceptional character of the last 30 years becomes apparent to everybody. We hope people start to realistically consider the climate situation in which the planet is at present.”