But the booming interest in climate change has transformed the study of ancient weather records from what was once a "wallflower science,'' says Christian Pfister, a climate historian at the University of Bern.
The accounts dispel any lingering doubts that the Earth is heating up more dramatically than ever before, he says. Last winter — when spring blossoms popped up all over the Austrian Alps, Geneva's official chestnut tree sprouted leaves and flowers, and Swedes were still picking mushrooms well into December — was Europe's warmest in 500 years, Pfister says. It came after the hottest autumn in a millennium and was followed by one of the balmiest Aprils on record.
"In the last year there was a series of extremely exceptional weather,'' he says. "The probability of this is very low.''