Paris:
Mountain glaciers shrinking due to climate change are less massive than previously thought, putting millions of people who depend on them for water supplies at risk, researchers reported Monday.
For example, glaciers in the Andes Mountains in South America were found to store 23 percent less freshwater compared to previous estimates, they wrote in the journal Nature Geoscience.
Bolivia’s largest city, La Paz, with more than two million inhabitants, relies heavily on glacier drainage for agriculture and as a buffer against drought.
As the slow-moving glacial rivers lose more mass through melting than they gain with fresh snow, the water flows become erratic — including periods of flooding — and eventually dry up, first in low-lying mountains and finally higher mountains.
Water from glaciers flowing into rivers is also crucial to hydropower generation and agriculture.
“Finding less ice is important and will affect millions of people around the world,” said study co-author Mathieu Morlighem, a professor of Earth Sciences at Dartmouth University.
Some regions, including the Himalayas, were found to have up to a third more ice than thought, “which will reduce pressure on water resources,” lead author Romain Millan, a postdoctoral researcher at the Institute of Environmental Geosciences in Grenoble, France, told AFP.
Globally, however, the satellite survey that covered 98 percent of the world’s glaciers — about 250,000 — found that the volume of all glaciers combined, above and below sea level, was 11 percent smaller than previous calculations.
On the silver lining are the implications for sea level rise, which is expected to be one of the most devastating effects of global warming.
Throughout the 20th century, melting glaciers were one of the leading causes of rising ocean levels, along with the expansion of seawater as it warms.
Like thick syrup
The new estimate lowers the potential contribution of glaciers to sea level rise from about 33 to 26 centimeters (13 to 10 inches).
But that reduction – while not insignificant – is incidental compared to the impact of melting ice sheets, which have become the main driver of rising sea levels in the 21st century.
The miles-thick blankets of ice in West Antarctica and Greenland contain enough frozen water to push oceans up to 13 meters.
Despite their apparent immobility, glaciers are in constant motion, propelled by gravity.
“We generally think of glaciers as solid ice that can melt in the summer, but ice actually flows like thick syrup under its own weight,” Morlighem said.
“Using satellite imagery, we can track the movement of these glaciers from space on a global scale.”
To create an ice flow database, the researchers studied more than 800,000 pairs of before-and-after satellite images of glaciers, including large ice sheets, narrow alpine glaciers, slow valley glaciers and fast tidal glaciers.
The high-resolution images, captured by NASA and European Space Agency satellites, took more than a million hours of computing time on supercomputers in Grenoble.
Scientists not involved in the study described it as a “first-rate study” and an “amazing new inventory” of how much ice there is worldwide.
“Because there is less ice stored in the world’s glaciers than we imagined, they will disappear sooner than expected, and so the communities that depend on their ice and water are more likely to suffer the worst effects of climate change,” said Andrew Shepherd. , director of the Center for Polar Observation and Modeling at the University of Leeds.
“In every corner of the planet, the seasonality of river water levels will change dramatically as glaciers melt.”
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