The famous snow-capped peaks of the Alps are fading fast and being replaced by vegetation cover -- a process called "greening" that is expected to accelerate climate change, a study said Thursday.

The research, published in Science, was based on 38 years of satellite imagery across the entirety of the iconic European mountain range.

"We were very surprised, honestly, to find such a huge trend in greening," first author Sabine Rumpf, an ecologist at the University of Basel, told AFP.

Greening is a well-recognised phenomenon in the Arctic, but until now hadn't been well established over a large scale in mountainous areas.

However, since both the poles and mountains are warming faster than the rest of the planet, researchers suspected comparable effects.

For their analysis, the team examined regions at 1,700 meters above sea level, to exclude areas used for agriculture. They also excluded forested areas and glaciers.

According to the findings, which covered 1984-2021, snow cover was no longer present in summer on nearly 10 percent of the area studied.

Rumpf pointed out that satellite images can only verify the presence or absence of snow -- but the first effect of warming is to reduce the depth of the snowpack, which can't be seen from space.

Secondly, the researchers compared the amount of vegetation using wavelength analysis to detect the amount of chlorophyll present, and found plant growth increased across 77 percent of the zone studied.

Greening happens in three different ways: plants begin growing in areas they previously weren't present, they grow taller and more densely due to favourable conditions, and finally particular species growing normally at lower altitudes move into higher areas.

"It is climate change that is driving these changes," said Rumpf.

"Warming means that we have longer vegetation periods, we have more benign conditions that foster plant growth, so plants can just grow more and faster," she added.