Each spring, during the annual Tour of Flanders, cyclists whiz through Belgium’s rolling countryside.

Pieter De Frenne and colleagues at Ghent University have been studying race footage from the past thirty-five years. But they’re not paying attention to the cyclists.

De Frenne: “We selected more than 40 different trees along the racetrack, and every year we simply looked for video footage or images of this particular tree.”

They wanted to see if the trees had leaves or flowers at race time.

De Frenne: “In the years before the 1990s, virtually none of the trees that we analyzed already had leaves. Whereas in the last 10 years, almost every year, the majority of the trees already started to produce either leaves or flowers when the cyclists pass by, and so you clearly see that spring has advanced much earlier.”

He says this is just the beginning of what scientists can learn from archived videos of annual outdoor events. The videos are time capsules that can reveal how climate change is affecting not only plants, but water levels, snow pack, and other natural resources.

Reporting credit: Elizabeth LoGiudice/ChavoBart Digital Media.