Source: Geophysical Research Letters
Glaciers in the Pyrenees mountains are disappearing before the eyes of researchers tracking their decline.
Of the 24 glaciers that remained in the Pyrenees in 2011, three have shrunk enough that they stopped moving in the past decade. This means that while some ice remains, they are no longer considered glaciers.
The total glacierized area in the Pyrenees dropped by 23.2% from 2011 to 2020.
“Nearly all the glaciers are still decreasing their surface [areas] at the same speed that they have been losing them since the 1980s,” said Jesús Revuelto, a postdoctoral researcher at the Spanish National Research Council and the corresponding author of a study published in August in Geophysical Research Letters. “We can argue with confidence that Pyrenean glaciers are in extreme jeopardy and could disappear or become residual ice patches in the next decades,” he said.
Revuelto and his colleagues flew drones equipped with digital cameras over glaciers from August through October in 2020. They used the photos to reconstruct the 3D surface with algorithms, then compared these to lidar analyses conducted in the same months in 2011 by the National Geographic Institute of Spain. They also examined the glaciers via satellite images and field surveys.
Glaciers are defined by movement—they flow slowly downhill, like ice rivers fed by snow at upper altitudes. As the snow piles up, gravity and the weight of the ice sheet push the glacier down through valleys and other topography. When a glacier stops moving, it loses its definition, becoming no more than a big sheet of ice and snow.
“If the ice of the glaciers is not moving anymore, this means that the glacier has disappeared,” Revuelto said.
The researchers found that three glaciers stopped moving through the Pyrenees during the past decade. Many more of the smaller dwarf glaciers will likely also lose their characteristic movement soon, Revuelto said.
Losing Five-Story Buildings
The researchers found that some glaciers were shrinking faster than others, depending on factors like topography that might give more shade to the ice sheets. In some areas, the glaciers have lost more than 20 meters (65.6 feet) of thickness. “Twenty meters is really high,” Revuelto said. “It’s higher than a building of five floors.”
Mauro Fischer, a lecturer and postdoctoral researcher in physical geography at the University of Bern in Switzerland who was not involved in the study, said in his work he has found similar problems with the smaller glaciers in the Swiss Alps. “They either shrink and die or they get disconnected,” said Fischer, “because they get really influenced by topographical factors.”
Fischer said that these smaller glaciers may not carry a lot of water individually, but together they make up 80%–90% of the ice sheets in the world’s low- to middle-altitude mountain ranges, so the melting can add up. These small glaciers are important sources of water for local villages and for the tourist community that relies on glacier water at hiking lodges and huts.
Fischer worries that the Pyrenees may become a glacier-free mountain range in the next 10–15 years.
Revuelto said that besides the loss of stored water, glaciers also provide important sources of knowledge. Ice cores can reveal much about past climates and environments, for example. But the Pyrenees also stand to lose a point of national pride that draws locals and tourists alike.
“It’s a patrimony that belongs to everyone,” he said. “We’ll lose this patrimony.”
(Geophysical Research Letters, https://doi.org/10.1029/2021GL094339, 2021)
—Joshua Learn (@JoshuaLearn1), Science Writer