Utrecht University: The consequences of climate change in the Alps are visible from space

Global warming has a particularly pronounced impact on the Alpine region. Like the Arctic, this European mountain range is becoming greener. Writing in the journal Science, researchers from Utrecht University, among others, have now used satellite data to show that vegetation above the tree line has increased in 77 percent of the Alps, bringing the unique biodiversity of the Alps under considerable pressure. At lower elevations, a decrease in snow depth has already caused some areas to become largely snow-free.

Melting glaciers have become a symbol of climate change in the Alps. Now, the reduction in snow cover is already visible from space but this is by no means the biggest change. This is the conclusion of an international team of researchers from Utrecht, Switzerland and Finland, who for the first time conducted extensive research on changes in vegetation production in the Alps.

We are now starting to see the phenomenon of ‘greening’ due to climate change in mountains.

Dr. Mathieu Gravey
The researchers investigated the change in snow cover and vegetation using high-resolution satellite data from 1984 to 2021. Over this period, the area above the tree line turned greener in more than three quarters of the area the researchers observed, as plants colonise new areas and vegetation becomes denser and taller. This phenomenon of ‘greening’ due to climate change is already well-documented in the Arctic, says Mathieu Gravey, assistant professor in Geo-Environmental Data Science at Utrecht University and coauthor of the new study. We are now starting to see the same phenomenon in mountains.

Pressure to the Alps’ biodiversity
“The scale of the change has turned out to be absolutely massive in the Alps,” says Sabine Rumpf, lead author of the study and assistant professor at the University of Basel. The authors show that the increase of plant biomass is primarily due to changes in precipitation and longer vegetation periods as a result of rising temperatures. As global warming continues, the Alps will turn greener and greener, creating a vicious circle: “Greener mountains reflect less sunlight and therefore lead to further warming – and, in turn, to further shrinkage of reflective snow cover,” says Rumpf.

Alpine plants are adapted to harsh conditions, but they’re not very competitive, she adds. As environmental conditions change, these specialised species lose their advantage and are outcompeted: The unique biodiversity of the Alps is therefore under considerable pressure.

Less snow cover
In contrast to vegetation, the extent of snow cover above the tree line has only changed slightly since 1984. Nevertheless, the change is worrying, Gravey emphasises. Ten percent of the areas we observed now have significantly less snow cover compared to 1984. The reason the change has only now been detected, the researchers theorise, is likely due to the lower satellite resolutions of previous studies.

For years, local ground-based measurements have shown a decrease in snow depth at low elevations, adds Grégoire Mariéthoz, professor at the University of Lausanne. This decrease has already caused some areas to become largely snow-free. Though satellite data only allow the researchers to draw conclusions about snow cover and not snow depth, those earlier local measurements help the researchers deduce changes in snow volume.

Warming also causes further melting of glaciers and the thawing of permafrost, which may lead to more landslides, rockfalls and mudflows. Furthermore, the researchers emphasise the important role of snow and ice from the Alps in the supply of drinking water and, not least, for recreation and tourism.

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