Half of Earth’s glaciers, including the smallest of them, are doomed to disappear by the end of the century because of climate change, a new study reveals on Thursday, but limiting global warming as much as possible could still help save others.
These works, published in the prestigious journal Scienceprovide the most accurate projections to date of the future of the world’s approximately 215,000 glaciers.
The authors warn of the importance of acting on the greenhouse gas emissions responsible for climate change, in order to limit the melting of these glaciers and its consequences, in particular on the rise in sea level and water resources. .
“I think there is a small ray of hope and a positive message in our study, because it tells us that we can make a difference, that actions matter,” Regine Hock, co-author of the study, told AFP. the study.
The particularity of this work is to study the direct effect on the glaciers of several scenarios of global warming (1.5°C, 2°C, 3°C and 4°C), in order to better direct political decisions.
If temperature rise is limited to 1.5°C above pre-industrial times – the most ambitious goal of the Paris climate agreement – then 49% of the world’s glaciers will disappear by 2100.
This loss will represent about 26% of the total mass of ice, because the smallest glaciers will be the first affected. The researchers estimate that the sea level will therefore rise by about 9 centimeters (an increase which will be added to that linked for example to the melting of the ice caps).
“Regions with relatively little ice, such as the Alps, Caucasus, Andes, or western United States, lose almost all of their ice by the end of the century, regardless of the emissions scenario,” explains Regine Hock, professor at the University of Oslo. “These glaciers are more or less doomed. »
If the temperature rise reaches 4°C, the worst scenario envisaged, then the largest glaciers, for example in Alaska, will be more affected: 83% of the glaciers would disappear, which represents 41% of the total mass of their ice, and a rise from the sea of 15 centimeters.
“It may not seem like a lot, from 9 cm to 15 cm” in elevation, Regine Hock, who has studied glaciers all her career, told AFP. But these levels are a “great cause for concern”, because the higher they are, the more they will cause major flooding in the event of storms, and therefore “much more damage”.
This is already the case, the sea level having already risen (about 3 mm each year).
Total deglaciation
At the moment, the world is heading for a warming of 2.7°C, which would lead to almost complete deglaciation in central Europe, western Canada and the United States, and even New Zealand.
These projections, which are more alarming than those currently used by UN climate experts (IPCC), have been made possible thanks to brand new data on the mass variations of each glacier in the world in recent decades. These data made it possible to better calibrate the mathematical model used to anticipate the future.
This also took into account processes that had not been integrated into previous studies, such as the effect of the covering of glaciers by debris (rock, etc.), or the detachment of icebergs into the sea from some glaciers (calving).
The glaciers studied represent only “1% of all the ice on Earth”, but they are “much more sensitive” than other expanses of ice, because they are often located in regions where temperatures are closer to the melting point.
They have thus “contributed to the rise in sea level almost as much as the ice caps of Greenland and Antarctica taken together over the past three decades”, underlines Regine Hock.
The disappearance of glaciers will also have consequences for water resources. They represent an important reservoir of water for around 2 billion people.
“In summer, in many regions, it is hot and dry, and the glaciers compensate for this loss of water,” explains the researcher. And their loss “is not just going to change the seasonality, […] there will also be less water in total. »
Boat traffic on lower rivers, or tourism around these small glaciers which are precisely the most accessible, will also be affected.
Limiting the disaster is still possible, underlines Regine Hock. But “as to whether that will happen is up to the policy makers. »