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Key figure: The world's glaciers have melted twice as rapidly over the last 20 years


This is one of the conclusions of a huge study carried out by scientists from the CNRS, CNES, IRD and the University of Toulouse III- Paul Sabatier and published on the journal Nature. It has for first time drawn up an exhaustive map of the world’s glaciers and their evolution. Ice is cracking and fragmenting everywhere more rapidly under the effects of climate change.

 An original study

On the left, a false colour representation of the data acquired by the Terra satellite cameras, here over the Ha-Iltzuk ice field in British Columbia (Canada). On the right, mapping of the cumulative thinning of these same glaciers between 2000 and 2019.

The Terra satellite, in orbit 713 km above Earth, has produced more than 500,000 images10. These images have permitted building a field model for each glacier, then measuring its evolution through time, notably its thickness. The exhaustiveness and spatial precision of this study have made it a new scientific working tool. Previous methods extrapolated data using ground measurements on several hundred reference glaciers and limited cover by satellite images or the study of gravimetric signals of lower resolution. This new study has considerably reduced the uncertainties.


Alarming results

The study has highlighted that the evolution of glaciers is not occurring synchronously around the world. Indeed, the effects of temperature and snowfalls must also be taken into account in their evolution. The melting of the cryosphere is one of the two factors underlying rising sea levels, with the thermal dilatation of water, due to climate change caused by greenhouse gas emissions. Glaciologists have calculated that glacier melting between 2000 and 2019 corresponds to a rise of 7.4 millimetres of the sea level per decade, i.e. 21% of the total observed. This corresponds to the immersion of England under 2 meters of water a year. The study showed that on average glaciers have lost 4% of their total volume over the last 20 years.


Rising water

This disappearance will have major consequences for more than 200 million people living in different territories around the world, firstly in the high valleys, and on the agriculture practised there. Also, the deltas, where 500 million people live, will be exposed to rising ocean levels. Regarding these forecasts, Romain Hugonnet, the leading author of the study and a researcher at the University of Toulouse, declared:

We have to act now. It might be difficult for the public to understand why glaciers are important, since they seem so far away, but they have an impact on many aspects of the water cycle, including on regional hydrology. By changing too quickly, they can provoke the deterioration and collapse of systems downstream”.

At this rate, the glaciers of the Alpes will have lost 80 to 90% of their mass by 2050. “If the temperature falls, the glaciers will grow again. But what’s happening now is that the impacts of human beings are occurring where their presence is absent”.

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