ANALYSIS – In the Alps, the melting of the glaciers is the most obvious sign of global warming. Some of them are already doomed, such as the glacier of Sarennes above the Alpe d’Huez. While the 5th report of the IPCC* on climate change is released today, climate experts are raising the alarm. Once again.
It is one of the indicators for climate change in altitude and one of the most observed glaciers in the world.
Studied since 1906, frequently analysed since 1948 by the scientific community, the glacier of Sarennes, situated in the massif of the Grandes Rousses, is now a mere shadow of itself, doomed to disappear from the alpine landscape by 2020.
The conclusion is clear. Between the snow falls in winter and the summer melting/thawing, the glacier has lost every year on average about 1,5 metre of ice thickness in the last thirty years. And since the mid eighties, the thawing has increased. « Over the last ten years, we’ve lost each year the equivalent of a 3-metre-layer of ice », observes Emmanuel Thibert, researcher at the Irstea (the national institute of research in sciences and technologies of the environment and agriculture, ex-Cemagref). The institute has indeed, in collaboration with the glaciology and geophysics laboratory of the environment at Joseph-Fourier’s university (LGGE), elaborated a real database on the evolution of glaciers (1). Every year for ten years now, 10 % of the ice thickness of the glacier of Sarenne is disappearing.
The climate is warming up… faster and faster
In forty years, the alpine glaciers have already lost one quarter of their surface area. What will be left at the end of the century? Assuming there is an increase in temperature of 3°C by 2100, only glaciers higher than 4000 metres will remain. The most famous of them, the Mer de Glace of Chamonix, would continue its retraction, from 800 metres to 1.2 Km in the next twenty years.
In the Alps, the thawing of the glaciers is certainly the most obvious sign of climate change. And the climate is warming up faster and faster, as the experts of the IPCC* confirm in their 5th report released today.
The assessment of ice masses is therefore a key witness to climate change in the mid and long term. This is an essential barometer while the scientific community is still facing unknowns. Predicting the future climate in the short term is a challenge for researchers. « We know how the climate will react in fifty years », continues Gerhard Krinner, « but we cannot predict today if the summer 2014 will be scorching or not. »
However, one thing is certain. For one century now and the first temperature readings in 1880, the earth has lived its warmest decade. The average global temperature has thus increased by 0,8°C since the end of the 19th century, leading to ever higher greenhouse gas emissions. And by the end of the 21st century, the thermometer could go up by 1,5 to 2°C, according to estimates of the climatologists.
The IPCC* is giving a fifth warning. « It is extremely likely that we are the main cause of the global warming observed since the mid 20th century », indicate the international experts in the summary of their report conveyed to the policy-makers. And they rub it in stating that: « Climate change will require substantial and sustainable reductions of greenhouse gas emissions ».
The glacier of Sarennes in 1906… and in 2005.
© E.Thibert LGGE
Evolution of the Mer de Glace of Chamonix.
© IGN
The warmest decade in a century
« The climate is warming up continuously », attests Gerhard Krinner, Director of Research at the CNRS and one of the main authors of the GIEC’s 5th report. « Each decade since 1850 has been warmer than the previous one. » And if warming has slowed down these last ten years, according to the scientists, it has not yet stopped completely, as shown with the continuous rising of sea levels and the thawing of glaciers.
The glacier of Sarenne semi-shade semi-light.
© Cédric Colomban
A new international agreement… in 2015
On the glacier of Sarenne…
© Cédric Colomban
The message is clear, before the upcoming international conference, planned in Paris in 2015 which should lead to a new agreement to try and keep global warming under the threshold of +2 °C. « We think that a temperature increase of 2 °C remains manageable. This is not necessarily the opinion of the IPCC*! », underlines Gerhard Krinner. « This is a political objective. Even if we want to respect this objective, we need to take action, and this very urgently. » Patricia Cerinsek Translation by Sandra Bailly, Translator / Desktop Publishing specialist
Phone : +33 (0)6 95 87 15 27 – email : sandra.bailly79 [at] gmail.com
(1) Five glaciers – Sarennes, Saint-Sorlin and Gébroulaz in Savoie, Argentière and the Mer de glace in Haute-Savoie – are part of the network Glacioclim, an environmental research observatory, focusing on the study of glaciers and climate. (2) This is the first section of the analysis of the IPCC*, dealing with the climate sciences. A second section related to the vulnerability of human activities and their adaptation to climate change, will be the topic of a report in March 2014 ; at last, a third section concerning the necessary measures for reducing the impact of climate warming, is expected for April 2014. The global synthesis report will be published at the end of October 2014. N.B: The increase of 1,5 to 2 °C of global average temperatures at the end of the 21st century is the most « optimistic » scenario of the IPCC*. In the pessimistic version, the thermometer should go up to 4,8 °C. Up to now, we have noted that the pessimistic scenario prevailed… * IPCC : Intergovernmental Panel on Climate Change
