Andean glaciers shrinking at unprecedented levels

New research shows Andean glaciers have retreated to lowest levels in 11,700 years

An international team of scientists has discovered the glaciers in the Andes have shrunk to their smallest size in 11,700 years, revealing the tropics have already warmed beyond anything experienced during the entire Holocene age.

Scientists have long predicted the world's glaciers will retreat as temperatures warm but the study's analysis of rock samples adjacent to four glaciers in the Andes Mountains shows that glacial retreat in the tropics has happened much faster and has already passed an alarming cross-epoch benchmark.

As Earth's climate heats up, the findings signal more of the world's glaciers are likely retreating faster than predicted, possibly decades ahead of the climatological schedule.

The findings have been published in the international journal Science and was led by Boston College in collaboration with scientists from University of Galway, UC Berkeley, University of Wisconsin, Tulane University, Aix-Marseille University, Aspen Global Change Institute, Ohio State University, Union College, Université Grenoble Alpes, and Purdue University.

When glaciers shrink, the underlying bedrock is suddenly exposed to the stream of cosmic radiation constantly bombarding Earth. Similar to a sunburn, this radiation causes microscopic nuclear reactions inside the bedrock that produce rare isotopes, such as beryllium-10 and carbon-14.

Scientists measure the concentration of these isotopes to calculate how long landscapes have been buried by ice and establish when glaciers were last as small as today. The rocks being exposed by melting glaciers in Colombia, Peru, and Bolivia contain such small amounts of cosmogenic isotopes that the researchers were able to conclude these tropical ice masses have not been so small for at least 11,700 years, and potentially much longer.

The rate at which the glaciers are melting suggests that the tropical climate can no longer be classified as belonging to the Holocene interglacial period, the last 11,700 years of relatively stable climate in which civilisation has flourished. Instead, the tropics may be best classified by a new period that will spell the end of glaciers in the high tropical Andes: the Anthropocene.

University of Galway climate scientist and co-author of the study, Dr Gordon Bromley led the collection of bedrock samples in the high Sierra Nevada del Cocuy in Colombia.

Dr Bromley said:"Glaciers are the poster child of human-caused global warming and are currently shrinking on a global scale as atmospheric temperatures rise. Our team uses glaciers as natural thermometers to track the magnitude of modern climate change and provide much-needed context of today's rapid ice loss. Using a revolutionary technique called cosmogenic nuclide surface-exposure dating, we have reconstructed the growth and decay of glaciers in the high-altitude tropical Andes, which is arguably the most sensitive environment on Earth to climate change.

"We found that modern glaciers in Colombia, Peru, and Bolivia are smaller today than they have been for the entirety of the Holocene interglacial and conclude that the magnitude of modern ice loss is unprecedented.

"This sets a grim new benchmark for our monitoring of human-driven climate change and also demonstrates how the high-altitude tropics, home to some of the most irreplaceable ecosystems on Earth, are also the most sensitive - and thus vulnerable - parts of our planet to global warming."

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