Alps: Climate change can be seen from space

Snow is slowly giving way to vegetation due to the effects of climate change. A study by the universities of Lausanne and Basel, published in the journal Science on Thursday, reveals the spread of vegetation in the Alps for satellite images taken between 1984 and 2021.

This is not good news. The Alps are becoming greener visually or rather in satellite view. In question? Climate change and rising temperatures. This is the conclusion of Swiss researchers who have analyzed high-resolution images of all the Alps taken from space in the last 38 years.

Sabin Rampoff, an assistant professor at the University of Basel and lead author of the study, told AFP on Thursday that “we are really surprised by this huge greening trend.”

In question: Decreased snow cover, and vegetation growth, due to rising temperatures. The phenomenon is already well-known in the Arctic, but so far little has been studied on a large scale for mountainous areas. However, these two places are warming much faster than the others on the planet, and researchers therefore suspect comparative effects.

Plants take precedence over snowpacks

For their analysis, they isolated areas above 1,700 meters above sea level, excluding areas used for agriculture. Above this height, forests were also excluded. Results: Observed at about 10% of the surface area, at the end of the analyzed period no more snow was present in the summer where it was at the beginning.

Sabin Rampoff also noted that satellite imagery allows us to simply verify the presence or absence of snow. However, the first effect of warming is to reduce the depth of the snowpack, which has been observed by local measurements. So “this may not seem like more than 10%, but that doesn’t mean nothing is happening in other regions”.

Second, the researchers compared plant quantities using wavelength analysis to determine the amount of chlorophyll present. The result was even more interesting: vegetation grew in 77% of the area observed.

A vicious cycle

Plants grow in three different ways: plants grow where no one has been before, some have grown and become denser due to more favorable conditions, and finally species are growing naturally at lower altitudes and growing faster and easily colonizing higher areas.

“It’s climate change that is driving these changes,” said Sabine Rampoff. “Warmth means a long growing season,” and “the warmer it is, the more rain falls as rain, not snow.”

The consequences of this “green” are multiple. First, a large portion of drinking water comes from melting snow, the study noted. If water is not stored as snow, it quickly disappears through rivers. In addition, the habitat of species specially adapted to the alpine environment is disrupted. And the disappearance of snow could also hurt the ski tourism industry. Finally, “what we want to forget is the emotional side of these processes, the Alps being a symbol, and when people think of Switzerland, they often think of the Alps,” said Sabin Rampoff.

For the future, the hope that a vicious circle has actually been set is not met. Snow reflects about 90% of solar radiation, absorbs plants much more, and then returns them as heat. Which accelerates warming, and therefore melts snow and grows vegetation. Etc.

An uncertain future for the Alps

However, the exact evolution of the Alps in the following decades remains unknown. “In terms of snow, it’s pretty clear. The snowpack will disappear further, especially at lower altitudes, “explained Sabin Rampoff. But another phenomenon for the moment, the transition to brown, indicates that the land is no longer covered with snow or vegetation, only less than 1% of the area studied has been detected. This is much less than what is observed in the mountains of the Arctic or Central Asia.

This tendency is fueled by two factors: an increase in the number of rainy seasons and then a drought, and the drying up of snow for plants. “We don’t know for the future that the brown transition will be more frequent and reverse the trend,” concludes Sabine Rampoff, who wants to be able to repeat these observations in a few years to verify this. .

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