Leave it to the French to measure global climate change through the archives of 600 years of harvesting the pinot noir grape in Burgundy.A group of French climatologists and ecologists has pored over records squirrelled away in parish papers and obscure municipal files to find which day the fabled grapes were picked in each year stretching back to 1370.
That harvest date falls precisely at the moment the grapes achieve perfect ripeness — and therefore the most glorious taste — and is tightly controlled by temperature, said Isabelle Chuine, a scientist at the Centre for Evolutionary and Functional Ecology in Montpellier, whose paper on her findings was published today in the journal Nature.
In homage to the splendour of this grape, which was developed in Burgundy many centuries ago, these dates have been reverently recorded year after year since the Black Death stalked the French countryside in the 14th century.
That means the harvest dates, worked backward through complex mathematical models, can be used to figure out variations in temperature, compared to the reference period of 1960 to 1989 — and not just for a few years, but in the longest uninterrupted line known in which the actual dates are written down.
(The findings jibe with more complex global temperature models such as those derived from tree rings and ice cores.)
The grape-harvest results surprised Dr. Chuine and the other researchers. They expected to find that temperatures in the 1990s were warmer than anything France had experienced in hundreds of years. Climatologists have said that the 1990s showed that global climate change, with its episodes of extreme weather, had set in.
Around the world, average temperatures rose through the 1990s, and catastrophic weather accompanied the trend: hurricanes, droughts, heat waves, deluges and thousands of heat deaths throughout Europe.
But when the French scientists crunched their grape numbers, they found that the land of the pinot noir had been about as warm as the 1990s in the 1380s, 1420s and 1520s, and then through the 1630s to the 1680s, only to cool off again.
Pascal Yiou, an applied mathematician at Gif-sur-Yvette, just south of Paris, who also worked on the paper, said the pinot noir figures are significant because they underline the fact that the warming trend through the 20th century is unprecedented.
While individual decades or years have been warm in Burgundy, the anomaly now is that the warming trend has kept going for more than a century.
That is a strong sign of climate change, he said.
The big shock, though, was the evidence from the summer of 2003, Dr. Chuine said.
In Burgundy, the temperature was far hotter in 2003 than it had been since the medieval grape harvesters began collecting data, the French researcher said.
The models showed that Burgundy was 5.86 degrees Celsius warmer than during the reference period. The next-highest anomaly was in 1523, when it was 4.10 degrees above the norm. In temperature terms, a difference of more than a degree is considered huge.
Worse still, said Dr. Yiou, is that the 2003 temperature “was completely unpredictable from what we knew before 2003.”
He said it could be a coincidence, or troubling evidence that climate is becoming more variable and therefore more unstable.
But he also said that the French are jumping on the data to figure out what they mean because 2003 was a catastrophic year for humans in France.
That year, 10,000 French residents died of heat.
It was a strange year around the world. The World Meteorological Organization called 2003 the third-warmest year around the world since 1861, when weather records began.
There were large wildfires in British Columbia, salmon suffocated in lethally warm streams, and a fierce drought plagued the Prairies.
Dr. Chuine said she has little doubt that global climate change was responsible for the strangeness of 2003.
ALANNA MITCHELL, Globe & Mail