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 video clips of that epic race one day. Not only was the weather atrocious, he noticed, but the trees along the roadside were bare. But in the past few years when he’d watched the race—a national Belgian obsession—he’d seen lush trees behind the riders.
Maybe, he thought, these videos hold more than just classic episodes in cycling history. Maybe, behind the spinning wheels, there is a hidden trove of data about how climate and biology had changed over time.
Plants respond to many different cues as they transition from winter to spring, like sunlight and heat. As the planet has warmed, what plants perceive as “spring” comes earlier than it used to, and the plants respond accordingly: leaves bud out and flowers perk to attention earlier than they have in the past. But one of the challenges scientists face is understanding exactly how sensitively plants respond to changes in climate and season. And to untangle that question, they need records of how plants behaved in the past.
De Frenne and his colleagues (several of whom are also cycling fans) had found a rich archive to draw upon. The Belgian national television service has video archives of the race going back to 1929—and the race passes the same exact spots every year at about the same date. So de Frenne and his colleagues could scan through the old video footage and find the exact same tree that the peloton pedaled past in 1980, 1990, 2000, up through today. (Learn about the man who recorded snow alone for 40 years—and the boon to science.)
Mining the Archives
The team decided to focus on the past 36 years, where the quality of the video was best. They sent Lisa Van Langenhove down to the video archives to watch over 200 hours of old tape.
“When I told my friends and family I was going to spend the summer watching cycling footage all day, I got some strange reactions,” she said. But she parked herself in a small, dark room for five weeks and started scrolling through years of footage.
She picked out a few dozen trees to follow from year to year. And for each spring from 1980 to now, she looked to see whether those trees were bare when the cyclists rode past, or whether they’d sprouted leaves.
They found that back in the 1980’s, branches were almost always bare on the race date—but now, the same trees almost always had leaves. In fact, over the ~40 year period, leaf emergence jumped up almost two weeks. (See how monks collected climate data for 700 years.)
That result is roughly in line with the data other groups have observed across Europe, says Josep Peñeulas, a biologist at the Universitat Autònoma de Barcelona, who was not involved with the study. For each degree warmer the habitat gets, trees leaf out a few days earlier.
Plants started shifting their leaf-outs earlier in earnest in the 1980s and 1990s as temperatures rose across the planet. And as spring comes earlier and earlier each year, ecological effects cascade—soil gets drier, birds and bugs arrive too late to their breeding grounds, and whole ecosystems start to change.
Long, detailed records like this one, showing just how plants responded to past changes in climate, can be invaluable to scientists who want to predict how floral and faunal communities might change in the future, says Mark Vellend, a biologist at the Université de Sherbrooke in Quebec.
“You have to be opportunistic: you can’t go back in time and start a study in 1980 by choice,” he says—and back in the 1980’s, no one knew how quickly the climate would change, so researchers weren’t specifically looking to keep track of plant responses. So biologists nowadays are constantly looking for creative ways to mine unexpected archives for data.
Elizabeth Wolkovich, an ecologist at the University of British Columbia, hopes the Belgian team—and others—take this technique farther. One of the most important things to learn, she says, is how plants behaved before warming really took off. The race video goes back to 1929 (though only in grainy black-and-white), so there’s a chance to build an even longer record.
But she also points out that this approach could be used elsewhere in the world, especially in the places were really good long-term records are sparse and climate changes have the most dramatic effects—like high alpine zones, or the Arctic.
She’d love for them to look at the Tour de France, or the Giro de Italia, or some of the other cycling races that reach the thin air of the high mountains. Or even better, to look to the Arctic.
“It’s unfortunate that we don’t have a cycling race in the summer where the Iditarod is held,” she says. “Because the Arctic is the place where we have the most extreme warming but also effectively have the least data.”