• An international study published Thursday in the prestigious journal

    Science

    predicts in its most optimistic scenario that half of the planet's glaciers will have disappeared by 2100.

  • A Toulouse laboratory took part in this work, which considerably aggravates, thanks to the consideration of new phenomena, the forecasts established so far.

  • These disturbing new data leave no hope for the glaciers of the Pyrenees and darken the horizon of those of the Alps.

A world where you would have to travel to the Himalayas, Alaska or the Russian Arctic to still have the chance to see a real glacier.

It is described in an international study, chilling in the back, published Thursday in the prestigious journal

Science

.

These jobs

significantly worsen the forecasts available so far, including those considered in the latest IPCC report.

In the most optimistic scenario – that of a global rise in temperatures confined to 1.5 degrees – the researchers estimate that 49% of the planet's 215,000 glaciers will have disappeared by 2100. In the worst case scenario, with + 4 degrees, 83% of the glaciers would melt completely.

Knowing that the calculation that holds the string currently table on a warming of about 2.7 degrees, the reality of the moment is between these two chilling forecasts, which surprised even the scientists who established them.

“Even in the most optimistic scenario, the ice losses are ultimately greater than expected.

The team was especially surprised by the results in terms of the number of glaciers that disappeared.

For small glaciers of less than 1 km2, the figures are staggering,” says Etienne Berthier, glaciologist at the Laboratory for Space Geophysics and Oceanography (Legos*) in Toulouse.

The latter provided the American team with his refined satellite observations, on the acceleration of the loss of mass of glaciers between 2000 and 2020. Overall, it goes from 14% to 23%.

Avoid the spread

Furthermore, the mathematical model used takes into account two new phenomena.

The first is the formation [the “calving”] of icebergs on the fracturing fronts of glaciers which end in a lake or in the sea. The second is the effect of dark debris, rocks or dust, which come to cover the glaciers when they retreat, like those that appeared in the Mer de Glace of the Mont Blanc massif.

“They can have two contradictory effects, explains the Toulouse researcher.

Either the layer of dust is very thin, it darkens the glacier, it captures solar energy better and it will melt faster, this is the albedo effect.

Either, when this layer becomes thicker and exceeds a few centimeters, it becomes insulating and prevents the melting of the ice located below”.



If the future upheaval of our mountain landscapes is inevitable, the authors of the work want to maintain a touch of optimism.

"It is too late for small glaciers but not too late to prevent this loss from spreading to all glacial regions," assures Etienne Berthier.

Keeping the rise in temperatures to reasonable levels between +1.5 and +2 degrees helps to preserve the largest glaciers at high altitudes.

And that means reducing our greenhouse gas emissions.

»

"In the Pyrenees, the case is folded"

But it will always be too late for the Pyrenees where "the case is over", according to the glaciologist, well aware of being a bird of bad omen.

“The twenty remaining glaciers are doomed.

They will be gone in ten to twenty years,” he predicts.

For the Alps, he maintains a glimmer of hope: “There are still differences between the scenarios.

If we manage to keep the temperature rise to just 1.5 degrees, we will keep 15% of the glaciers.

On the other hand, if we follow a scenario of a 4% increase, almost 99% of the glaciers will disappear.

".

Obviously, the work is accompanied by a "range" for the rise in water levels due to the melting of the glaciers.

It is between 9 and 15.4 cm, but does not take into account the melting of the ice caps or the expansion of the oceans.

In this area, the overall forecast of the IPCC is for a rise in water levels of 60 to 80 cm by the end of the century, with the risks of flooding that go with it.

Etienne Berthier also draws attention to the role of "water towers" played by glaciers with their ability to store water in the winter in the form of snow and to release it downstream in the summer "when the ecosystems need it the most”.

Beyond landscapes and tourism, whole sections of the economy and mountain life are threatened.

* CNRS/Cnes/IRD/Paul-Sabatier University

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