Unprecedented summer melting of Swiss glaciers: statistically impossible – yet it happened

A combination of winter drought, prolonged spring drought and summer drought and intense heat waves, has created a perfect storm for the Swiss glaciers. However, it’s safe to assume that the below described situation is not just the case for Swiss glaciers. Also French, Italian, German and Austrian glaciers have the same problem: unprecedented melting has occured.

How unprecedented? Well: statistically it’s virtually impossible. In case you are not familiair with statistics: in a stable system, about 68% of all measurements would fall around the mean of a population. 34% above this mean, and 34% below. This is known as a “standard distribution” and is used a lot in many analyses. This standard distribution has a deviation from this standard, expressed as “sigma”. More than 99% of all observations fall within + or – 3 sigma from the mean.

This year though, on some glaciers, a deviation of 4 sigma was found. Other stations have reported ice loss where it’s never observed before, for instance on the Jungfraujoch at 3400m. When we say “ice loss”, it’s a loss of mass due to net-melting. These locations typically lose balance only by flowing to lower altitudes and not by melting itself.

Climate change at work

Although it seems to be an anomaly, it is presumably getting more normal. Heat intensifies itself and drought exacerbates the problem. Glaciers create their own climate and their own cooling system. When mass is lost, the efficiency of a glacier to create it’s own climate decreases.
The issue with drought is the fact that most precipitation at high altitude falls as snow. Even in the midst of summer, high altitude precipitation is snow. This means that in a precipitation-rich summer, the glaciers do get fresh snow. This fresh snow adds of course balance to the glacier, but also a protective sheet of fresh snow ánd a higher albedo. The latter is the amount of light being reflected, rather than absorbed.
A warm, but wet summer can add a lot of snow at high altitudes – even when the base is in the ablation zone is losing a lot of ice.

In a dry winter, there is little snow falling to form a protective layer over the bare ice. This smaller amount of snow is blown away or melts faster, exposing the underlying ice. Under “normal” conditions, the ice receives occassional protection. In a dry year, this protection isn’t there. Solar energy is absorbed and bed rock becomes exposed much earlier in the year. But in this case, also to a much greater altitude, and for very long periods of time.

Just compare the 2 pictures below, from the Aiguille des Glaciers (3816m) in France. The pictures are taken from a different position – but only 1 month apart (June 25, 2022 and July 25). As you can see, there was already not a lot of snow in June. But in July, the glacier was completely uncovered by snow until about 3600m(!). The full summit pyramid was exposed to the direct heat, as no snow or ice is left to protect the rocks – and prevent them from falling.

Laat een reactie achter