Less snow and less time: this is a phenomenon already well known to those used to alpine slopes, which is demonstrated in a comprehensive study carried out over the past five decades on the scale of the entire European massif.
Nearly a month of snow cover has been lost in the whole of the Alps at low and medium altitude for half a century, say the thirty researchers who signed the article in the journal. The Cryosphere. Between 1971 and 2019, the period during which there is snow on the ground each winter reduced on average from 22 to 34 days in the Alps, below 2,000 meters above sea level, they estimate.
This study makes it possible to “Give an overview of climatic snow cover trends”, explains Samuel Morin, co-signer and director of the National Meteorological Research Center (Météo France / CNRS).
A “fundamental trend”
The observed decrease in snowfall in the mountains is a “Underlying trend, which confirms previous studies”, carried out at local or national levels. “We really have a global analysis of snow cover at the scale of the whole of the Alps”, summarizes this researcher.
To calculate these estimates, the scientists gathered and standardized very disparate observational data, coming from 2,000 weather stations in six countries (Italy, France, Germany, Austria, Slovenia, Switzerland), to form a homogeneous database.
→ READ. The melting of the ice has accelerated sharply in three decades
Their observation is clear: snow cover is reduced in the Alps. The number of days between the first snows in November-December and the spring melt continues to diminish, by around 5 days per decade below 2000 meters above sea level.
Decreased snow depth
And, when there is snow, there is less: over the whole season, the average snow depth between 1000 and 2000 meters above sea level in the north of the Alps has dropped by 2.8 cm per decade. This decrease is more marked in the south of the Alpine arc: researchers estimate the decrease there at 4.1 cm per decade.
Climate: the Anthropocene, or the era of “dazzling” disturbances
This slow erosion can be explained by a scissor effect: on the one hand, the same winter precipitation brings more rain than snow than before, which reduces the formation of the snowpack; on the other, the latter melts more quickly.
” Everything leads to believe “ that this long-term dynamic – which erases strong variations from one year to the next – is caused by global warming, even if the search for the causes is not the object of the study.
Global warming involved
It is “Above all the warming that plays”, estimates Samuel Morin, former director of the Center for Snow Studies at Météo France. This trend is much less clear for high altitudes, where it is colder, he says.
“Whatever we do in terms of greenhouse gas emissions, we will have a reduction in snow cover at low and medium altitude which will be between 10% and 40%” by 2050, he says.