World’s glaciers 'contain less ice than thought'

Mountain glaciers shrinking due to climate change have been found to be less voluminous than previously understood, putting millions who depend on them for water supply at risk.

Researchers published their findings on Monday in the journal Nature Geoscience, reporting that globally the volume of all glaciers combined, above and below sea level, was 11 percent smaller than earlier calculations.

"The finding of less ice is important and will have implications for millions of people living around the world," said co-author Mathieu Morlighem, an Earth sciences professor at Dartmouth University.

Glaciers in the Andes Mountains of South America, for example, were found to store 23 percent less fresh water compared to earlier estimates, the researchers wrote in the journal.

Bolivia's largest city La Paz, with more than two million inhabitants, is highly dependent on glacier runoff for agriculture and as a buffer against drought.

As the slow-moving rivers of ice lose more mass through melt-off than they gain with fresh snow, water flows become irregular, including periods of flooding, and eventually dry up - first in low altitude mountains and eventually in higher ones.

Water from glaciers flowing into rivers is also crucial for hydropower generation and agriculture.

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‘First class study’

The new estimate lowers the potential contribution of glaciers to sea level rise from about 33 to 26 centimetres (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 cause of rising sea levels in the 21st century.

The kilometres-thick blankets of ice atop West Antarctica and Greenland hold enough frozen water to lift oceans some 13 metres.

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 caps, narrow alpine glaciers, slow valley glaciers and fast tidewater glaciers.

The high-resolution images, captured by NASA and European Space Agency satellites, required more than one million hours of computational time on super-computers in Grenoble.

Scientists not involved in the research described it as a "first class study" and a "great new inventory" of how much ice there is worldwide.

"Because there is less ice stored in the world's glaciers than we had thought, they will disappear earlier than expected and so the communities that depend on their ice and water will experience the worst effects of climate change sooner," said Andrew Shepherd, director of the Centre for Polar Observation and Modelling at the University of Leeds.

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