Using modern weather data and ancient records of grape harvests, researchers have divined summer climate patterns in parts of Switzerland as far back as the late 1400s.
Temperature strongly influences the growth of grapevines and the ripening of their fruit, which makes the plants excellent climate sensors, says This Rutishauser, a climatologist at the University of Bern. He and his colleagues looked for climate clues in grape-harvest data for 15 locations in northern and western Switzerland.
Rutishauser says that grape-harvest data are available back to 1600 for all but a few years, such as 1879 to 1884, when various pests and diseases devastated Swiss vineyards. Gaps in harvest data are more frequent between 1480 and 1600, he notes.
The researchers developed a climate model using data for the years from 1928 through 1979 and then verified it with data gathered from 1980 to 2006. Grape-harvest dates correlated most strongly with average temperatures for the months of April through August, Rutishauser and his colleagues note in the Oct. 28 Geophysical Research Letters. On average, each 1°C increase in average temperature for that interval brought the grape harvest forward 12 days.
Switzerland’s earliest grape harvest occurred in 2003, when a record-setting heat wave enveloped much of Europe (SN: 7/3/04, p. 10). The hottest decade before recent times was the 1580s, which falls near the end of a time known as the Medieval Warm Period in Europe.
The region’s latest grape harvest took place in 1816, when global temperatures were much cooler than average because an immense volcanic eruption had occurred the year before. The coolest decade was the 1740s, which falls within an extended cold spell commonly called the Little Ice Age.