Glaciers hold less water than estimated, study finds – Orange News

AFP, published on Monday, February 07, 2022 at 5:55 p.m.

Mountain glaciers, which are melting under the effect of warming, contain less ice than scientists thought, according to a study published on Monday, which emphasizes the risks of access to water in certain regions, such as the Andes .

“The discovery that there is less ice is significant and will have consequences for millions of people around the world”, who depend on glaciers during the summer for their water supply, explains in a press release one of the authors, Mathieu Morlighem, from Darmouth College in the United States.

Far from being immobile, glaciers are masses of ice that flow under the effect of their weight. Knowing this flow velocity therefore makes it possible to determine the mass of the glacier. But until now, “we did not know this speed well”, explains to AFP the main author of the study Romain Millan, of the Institute of Environmental Geosciences in Grenoble (France).

So the researchers sifted through hundreds of thousands of satellite images of glaciers, comparing the advance over time of crevasses and rocks to measure this flow speed and come up with an atlas estimating the thickness of 98% of the more than 200,000 mountain glaciers on the planet (which excludes the gigantic glaciers at the edge of the ice caps).

At the global level, results published in the journal Nature Geoscience show that these glaciers are thinner than previously thought.

“If all the mountain glaciers were to melt, their contribution to sea level rise would be 20% lower” than previously estimated, specifies Romain Millan. That is a potential contribution of about 26 cm.

Good news ? Not really. The melting of mountain glaciers is marginal in terms of sea level rise, compared to the potential of the Greenland and Antarctic ice caps.

“Even if the glaciers contain enough ice to raise the sea level by some 25 cm, there is enough ice in the ice caps to raise this level by more than 60 meters”, notes Martin Siegert, co- Director of the Grantham Institute for Climate Change and the Environment, not involved in the study.

– “Disappear sooner” –

On the other hand, the impact is potentially devastating for the populations which depend on the glaciers for drinking, for agriculture or for hydraulic energy.

Certainly, the study shows significant regional differences and some glaciers are much larger than estimated, especially those in the Himalayas which contain 37% more ice.

But conversely, the water reserves of the Andes glaciers are about 27% lower than previously estimated.

Consequence: for example, in the basin of La Paz in Bolivia, where a third of the water resources come from the melting of the ice during the dry season, “it is inevitable that the reduced reservoir of ice will have an impact sooner than ‘anticipated,’ write the researchers.

Under the effect of global warming, glaciers are melting faster and faster. In a special report in 2019, the UN’s Climate Panel (IPCC) estimated that low-lying glaciers like those in the Alps could lose 80% of their volume by 2100 and many could disappear altogether. .

But this new study could change that. “We call on the community of glaciologists to use these new estimates to re-estimate the evolution of glaciers”, indicates Romain Millan.

“Because there is less ice stored in glaciers than expected, they will disappear sooner than expected,” said Andrew Shepherd, director of the Polar Observation and Modeling Center at the University of Leeds, who did not take part in the study.

So the communities that depend on this water “will suffer the worst effects of climate change sooner”, he continues.

The authors of the study note, however, that information on glaciers is still partial and deserves to be confirmed by collecting data in the field, which is difficult for glaciers that extend over several countries, notes Romain Millan.

In the meantime, to help states better prepare for the impact of global warming on glaciers, researchers are working on simulations of the evolution of water resources over time.