• Glaciers lost 298 gigatonnes of ice mass annually between 2015 and 2019, according to our partner The Conversation.

  • However, a climatic tipping point in the mountains could lead to the loss of water reservoirs (ice and snow) with repercussions on agriculture, industry, biodiversity and human society as a whole.

  • Glaciers lost 298 gigatonnes of ice mass annually between 2015 and 2019, according to our partner The Conversation.

We all know dramatic examples of the climate change the planet is going through, and so do we.

The pack ice is melting, the heat waves are increasing, the forests are being ravaged by gigantic fires.

In the mountains, the glaciers are disappearing and the snow is less and less present.

Thin and not extensive, the snowpack liquefies early in spring and appears later in autumn and winter.

The decrease in glacial mass has accelerated sharply since the beginning of the 21st century: between 2000 and 2004, glaciers lost 227 gigatonnes annually, and this loss rose to 298 gigatonnes per year between 2015 and 2019, according to a study .

As a result, the vegetation growth period – during which the air temperature remains above 5°C – increases.

Is this a good thing?

No, as we can understand in the video below.

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"Understanding climate change in the Alps" (CREA Mont-Blanc)

What does science know about climate change in the mountains and why is it stronger there than in the plains?

Warming depends on altitude: this has been verified on a global and regional scale.

Thus, it occurs more quickly at altitude where its impact will then be felt more strongly.

While these concrete effects of climate change can be measured and linked to a global increase in CO2 in the atmosphere, the mechanisms at work are not fully understood, especially in mountain areas.

Does that surprise you?

And yet, science does not yet know everything about everything!

negative spiral

A first mechanism to consider is the capacity of a surface to reflect light, which is called the albedo.

White surfaces, such as snow, reflect more solar radiation than dark surfaces (and therefore have a higher albedo).

Therefore, the reflected radiation will not heat these clear or white surfaces.

On average, land surfaces reflect about 30% of sunlight, but this ability is significantly increased for snow-covered mountains, with for example a 70% albedo detected in the Swiss mountains observed in this study.

Fresh snow can reflect up to 87% of radiation.

Early snowmelt and retreating glaciers leave land rocky and barren for longer periods of time.

These barren lands reflect less solar radiation than white snow or ice.

As a result, these places warm up and also retain heat longer.

We then enter a negative spiral which further amplifies the effect of global warming, especially in the alpine areas.

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Behind the scenes – strong impacts of climate change in the mountains (EP #04)

Sahara dust clouds

Other phenomena can further accelerate the melting of snow in the mountains.

In March 2022, France and other European countries experienced episodes of Sahara dust clouds, which covered snow and ice in mountain areas with a sand-colored layer, decreasing their reflective capacity (albedo) .

The tinted snow absorbs more heat and melts faster.

With accelerating climate change, such events are becoming more frequent and reinforce early melting.

​Surface humidity and evapotranspiration

A study conducted on the Tibetan Plateau, where warming accelerated during the winter months in the late 20th century, shows that rising temperatures have been linked to rising surface humidity.

The increase in surface humidity leads to an increase in long-wave radiation (=heat) and can locally and temporarily increase the temperature at altitude.

But locally, in the mountains, it has been shown that an increase in winter surface vapor leads to heat and therefore higher temperatures, a phenomenon which intensifies with altitude.

As a less cold winter is also less dry, the process can get out of hand.

In general, evapotranspiration, i.e. transpiration from vegetation and water bodies, can also contribute to temperature changes.

Like the perspiration of a human body, evapotranspiration can cool the air and the environment, an effect that can be seen walking through a forest in the summer.

In the mountains, prolonged droughts therefore reinforce the rise in temperatures, because the lakes and vegetation dry up and no water evaporates.

Such effects can be observed in all ranges, but are more pronounced in tropical mountains.

​Trapped heat

Another process leading to increased temperatures can be explained by the Stefan-Boltzmann effect.

The Stefan-Boltzmann law describes the power radiated by a black body as a function of its temperature and describes the radiative forcing.

Radiative forcing occurs when the amount of energy entering Earth's atmosphere is different from the amount of energy leaving it.

In the mountains, the Stefan-Boltzmann effect describes the energy that is trapped in rocks and soils and is not entirely re-emitted.

This can also lead to higher temperatures, especially in rock-dominated alpine landscapes.

The final mechanism that science suggests may contribute to the increased sensitivity of mountains to climate change is the change in vegetation cover with altitude.

These cover changes may be associated with the migration of plant species to higher elevations to follow changes in temperature, including the upward shift of the treeline boundary.

These changes then influence the albedo of the surface, the distribution of energy fluxes and therefore lead to increases in temperature with altitude.

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Drought in the mountains, a problem for all of us!

​Tipping point and runaway process

All of these different processes can work in synergy and lead to tipping points in mountain regions, where the melting of ice and snow will be further accelerated and become unstoppable.

In Earth's history, several of these runaway processes were behind previous climate change events, which led to mass extinctions.

OUR “MOUNTAINS” FILE

A climatic tipping point in the mountains could lead to the loss of water reservoirs (ice and snow), aggravating droughts or floods in the mountains and in the plains, with repercussions on agriculture, industry, biodiversity and human society as a whole.

This analysis was written by Dirk S. Schmeller, Professor of Conservation Biology, Axa Chair in Functional Mountain Ecology at the École Nationale Supérieure Agronomique de Toulouse, University of Toulouse III – Paul Sabatier.



The original article was published on The Conversation website.


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