for National Geographic News
Connoisseurs may pore over grape-harvest records in search of the perfect vintage of wine. But a team of French scientists and historians is toasting the same records for the insights they yield on past climate.
In Burgundy, France, as in other parts of Europe, the first officially decreed day of grape harvesting has been carefully noted in parish and municipal archives for at least 600 years.
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Using a scientific method known as phenologyin which the onset of various stages of plant growth are correlated with climatethe team was able to reconstruct spring and summer temperatures in Burgundy from 1370 to 2003. The findings are based on the harvest dates of pinot noir grapes.
According to the reconstructed temperature record, warm summers like those of the 1990s have occurred several times in Burgundy since the 14th century. The heat wave of summer 2003, however, was the hottest ever for western Europe.
"The year 2003 is a record in the sense that this has never been seen at any time since the Middle Ages," said Pascal Yiou, a climatologist with the Laboratoire des Sciences du Climat et de l'Environnement in Gif-sur-Yvette, France.
Yiou and his colleagues' findings wilil be published in tomorrow's issue of the science journal Nature.
Annette Menzel, a climate researcher in the department of ecology at the Technical University of Munich in Germany, is publishing similar results. His are based on an index of grape-harvest records throughout western Europe and will be featured in an upcoming issue of the atmospheric-science journal Meteorologische Zeitschrift.
"According to my analysis, summer of 2003 was really an extreme one," she said.
To find out what the temperature was one year ago or a hundred years ago, scientists can usually find the information as recorded by a thermometer. But these instruments were not invented until the early 17th century and only gained widespread use by the late 19th century.
To determine what the temperature was prior to then, scientists turn to phenology. The method correlates events to their required temperaturessuch as when a tree gets its first leaves, or flowers, or when its fruit ripens.
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