The Alps are getting greener and greener

Green trees are seen in front of the snow-capped Alps mountains.

Photo: JEFF PACHOUD/AFP (Getty Images)

A team of researchers studying satellite images of the Alps have made a disturbing discovery: Since 1984, most high-altitude parts of the European mountain range have seen an increase in vegetation. While it doesn’t seem particularly bothersome, this “greening” is likely due to global warming and may facilitate a feedback loop that also reduces snow cover.

“When snow and ice recede, vegetation develops, and this is called greening,” Antoine Guisan, professor of ecology and evolution at the University of Lausanne, told me by phone. . Guisan is co-author of a paper about research, which is published in the journal Science this week. Sabine Rumpf, assistant professor at the University of Basel, led the study.

The team collected satellite images taken of the Alps from 1984 to 2021, giving them a comprehensive overview of how vegetation and snow cover have changed over four decades. They specifically studied elevations above 1,700 meters (5,580 feet) – this elevation marks the tree line. “The human influence becomes more and more powerful below this altitude,” Guisan said, so excluding areas below the treeline helped them focus on changes that might be due to climatic factors. .

The researchers studied satellite data from the Alps to determine vegetation trends.  In this view, the darker the green, the greater the increase in vegetation.

Researchers studied satellite data from the Alps to determine vegetation trends. In this viewthe darker the green, the greater the increase in vegetation.
Screenshot: Google Earth Engine, Grégoire Mariethoz

Rumpf, Guisan and their colleagues found that significant greening occurred in 77% of the high altitude Alps. They analyzed satellite images pixel by pixel to get an idea of ​​the evolution of vegetation and snow cover. Guisan explained, “For the millions of pixels we had for the Alps, we did a per-pixel analysis, and that analysis could either show an increase, or no trend, or a decrease.”

Instead of looking at all 12 months of the year, the team pulled data from June to September, because that’s when snow cover is most likely to change. “If you have snow from the beginning of June to the end of September, in one place, that means you have it all year round,” Guisan explained. Permanent snow cover has shrunk by more than 9% of the surveyed area, they found.

Although additional plants don’t sound so bad, greening the Alps could have serious human consequences. Vegetation reflects less light than snow, which means it absorbs more heat, which contributes to additional warming. This could cause a snowpack-loss feedback loop: more greening could result in more snowpack loss, which could lead to more greening. Annual melting of mmountain snow is an important source of water for municipalities around the Alps.

“Generally, snow provides water not only to mountain communities but also to lowlands,” Guisan said. A loss of snow cover could also affect skiing tourism in the Alps, as well as increasing the potential for landslides, he said.

Greening has been documented in other parts of the world, but Guisan said this research aims to fill a research gap. “So far, [greening] was mostly reported in the Arctic, but much less in the mountains,” Guisan explained.

While the most dramatic the impacts of climate change are currently being observed in the Arcticstudies like this remind us that the impacts of global warming will be felt everywhere, with domino effects that are difficult to predict.

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