Less white – much more green: An evaluation of satellite images from the last 38 years documents how climate change in the Alps has led to a reduction in snow cover and an increase in plant productivity above the tree line. Accordingly, the vegetation increased significantly in around 80 percent of these altitudes. A decline in the average snow cover can be seen in ten percent of the areas. The researchers say that the trends could lead to a self-reinforcing effect. According to them, this will probably have a critical impact on the further development of the Alpine region.
Ice is melting, deserts are expanding and the weather is going crazy: In many regions of the world, the problematic consequences of climate change are becoming increasingly apparent. In addition to the arctic areas, the mountain regions are particularly affected because they are warming up about twice as fast as the global average. This is reflected particularly impressively in the retreat of the glaciers in the European Alps. But researchers have also reported other significant changes. There are also signs of a clear change in the vegetation in the mountainous region and the snow cover at lower altitudes is decreasing. The researchers led by Sabine Rumpf from the University of Basel, on the other hand, now focused their attention on the area above the tree line. They looked at these altitudes using satellite images from space.
As they explain, the comprehensive analysis of this area was of particular importance, because there the trends in the development of snow cover and vegetation appeared by no means clear. Because it is difficult to assess how the complex climatic effects in the course of climate change will affect precipitation and thaw effects in these locations. It is also unclear how the living conditions for plants are changing: in addition to possible positive effects, browning due to unfavorable climatic changes is also known from some mountain regions in Asia. In order to provide comprehensive overview data in the Alpine region, Rumpf and her colleagues examined the change in snow cover and vegetation above 1700 meters using high-resolution satellite data from 1984 to 2021.
snow loss and vegetation growth
Their evaluations show: During the period of investigation, the plant biomass above the tree line increased significantly on more than 77 percent of the areas examined. Previous studies, on the other hand, have mainly dealt with the influence of global warming on biodiversity in the Alps and with changes in the distribution of plant species. Now the greening effect as a result of climate change in the Alps, as has already been well documented in the Arctic, is becoming clear. However, the researchers only found browning on one percent of the area examined. The researchers explain that the Alpine heights are becoming greener because plants are colonizing new areas there and the vegetation is generally denser and taller. “The extent of the change is very clear,” emphasizes Rumpf. The results also reflect that the increase in plant biomass is mainly due to changes in precipitation and longer growing seasons as a result of rising temperatures.
As far as snow cover is concerned, the study results show that since 1984 it has decreased significantly on around ten percent of the areas. Compared to the change in vegetation, this development appears to be less serious. However, according to the researchers, it is still a worrying trend that was not previously apparent. “Local measurements on the ground have been showing a decrease in snow depth at low altitudes for years. This decline has already meant that some areas are often largely snow-free,” says co-author Grégoire Mariéthoz from the University of Lausanne. The current study now provides information on how snow cover is developing at higher altitudes.
Trend with feedback loop
According to the researchers, it is now becoming clear how the white of the Alps is disappearing in favor of the green as global warming progresses. According to them, it is also problematic that this is associated with a self-reinforcing effect: “Greener mountains reflect less sunlight and therefore lead to further warming – and thus to a further shrinkage of the reflective snow cover,” says Rumpf. The researchers emphasize that the warming is also associated with other critical effects: the subsoil in the high Alps could increasingly start to slide and cause rockfalls and mudslides in the valleys.
At least the increase in vegetation binds more of the greenhouse gas carbon dioxide, one might think. But as the researchers explain, there is hardly any net benefit. Because the CO2 binding capacity of the Alpine vegetation is comparatively low. On the other hand, their warming effect could contribute to the thawing of the permafrost, which is associated with an increased release of greenhouse gases. The greening trend does not benefit the high alpine ecosystems either: “Alpine plants are adapted to harsh conditions, but they are not very competitive,” says Rumpf. When environmental conditions change, these specialized species lose their advantage and are pushed out: “The unique biodiversity of the Alps is therefore under considerable pressure”.
Ultimately, the study once again clarifies how climate change could change the ecologically and economically important Alpine region in a complex and problematic way, the scientists conclude.
Source: University of Basel, specialist article: Science, doi: 10.1126/science.abn6697