Glaciers around the world are collectively losing around 267 billion tonnes in mass every year, a study suggests.

Researchers say this yearly mass loss accounts for 21% of the observed sea-level rise.

The findings, published in the journal Nature, are based on high resolution mapping more than 200,000 glaciers across the planet.

The experts said understanding how glaciers melt over time, and how this contributes to rising sea levels, could help predict future changes and could inform strategies to manage water resources and mitigate sea-level rises.

Romain Hugonnet, of Laboratoire d’Etudes en Geophysique et Oceanographie Spatiales, Universite de Toulouse in France, along with his colleagues, analysed a diverse archive of half a million satellite stereo images as well as aerial images to study mass changes of individual glaciers.

The researchers then estimated the change in surface elevation, which is the height above sea level, of 217,175 glaciers around the globe, excluding ice sheets, between 2000 and 2019.

They found global glacier mass loss to have accelerated during the past two decades, at a rate of around 48 billion tonnes per year each decade since 2000.

The researchers said their findings “could explain 6–19% of the observed acceleration of sea-level rise”.

The study authors wrote: “About 200 million people live on land that is predicted to fall below the high-tide lines of rising sea levels by the end of the century, whereas more than one billion could face water shortage and food insecurity within the next three decades.

“Glaciers distinct from the ice sheets hold a prominent role in these outcomes as the largest estimated contributor to 21st century sea-level rise after thermal expansion and as one of the most climate-sensitive constituents of the world’s natural water towers.”

Commenting on the findings, Andrew Shepherd, professor of Earth observation at the University of Leeds, who was not involved in the study, said: “Glacier melting accounts for a quarter of Earth’s ice loss over the satellite era, and the changes taking place are disrupting water supplies for billions of people downstream, especially in years of drought when meltwater becomes a critical source.

“Although the rate of glacier melting has increased steadily, the pace has been dwarfed by the accelerating ice losses from the Antarctica and Greenland, and they remain our primary concern for future sea level rise.”