Snowflakes pelted down on the mass of cyclists knotted together at the starting line of the prestigious Liège-Bastogne-Liège race in Belgium one morning in late April 1980. Snow fell so thickly that the riders could barely see the road, and temperatures dipped below freezing. Cyclists quit by the dozens in the first hour. Seven hours later, a winner finally crossed the finish line, with frostbite so severe that he never regained feeling in two of his fingers.

“This was one of the most heroic editions of the race of all time,” says Pieter de Frenne, a cycling fan and ecologist at Ghent University in Belgium.

De Frenne, who studies the way plants respond to climate change, was idly watching old