Madison Reporter

Researchers at the University of Wisconsin–Madison and their collaborators have found that glaciers in the tropical Andes Mountains are now smaller than at any point since the end of the last ice age 11,700 years ago. This finding suggests that these high-altitude tropical ice fields may be the first to shrink beyond historical levels due to the warming global climate.

"We think these are the canary in the coal mine. The tropics would probably be the first place you’d expect ice to disappear, and that’s what we’re seeing," said Shaun Marcott, a professor of geoscience at UW–Madison. Marcott conducted this research with colleagues from Boston College and Tulane University. Andrew Gorin, formerly a graduate student at Boston College and now at the University of California, Berkeley, led the study published in the August 2, 2024 issue of Science.

Glaciers typically grow when summer temperatures are not warm enough to melt all of winter's snowfall. However, satellite imagery and on-the-ground observations have shown that high-altitude glaciers in the Andes are shrinking as warmer temperatures cause them to melt faster than snow can replenish them.

The researchers analyzed bedrock geochemistry near four glaciers in the high tropical Andes using satellite imagery to select sites exposed by melting ice within the last two or three decades. They looked for beryllium-10 and carbon-14 isotopes in quartz crystals within bedrock samples. These isotopes accumulate only when rock is exposed to cosmic rays at or near Earth's surface.

The team found "remarkably low" concentrations of both isotopes in nearly all samples, indicating recent exposure due to melting ice rather than erosion. "It’s highly unlikely this is from erosion," Marcott stated. "Because the multiple locations we went to all show the same thing."

This consistency led researchers to conclude that tropical glaciers, primarily located in the Andes, are shrinking beyond historical levels observed during recent geological periods.

"Glaciers are very sensitive to the climate system that they live in," Marcott added. "They really are the place you would look to see some of the first big changes resulting from a warming climate."

This research was supported by grants from the National Science Foundation (EAR-1805620; EAR-1805133; EAR-1805892).