The mountain glaciers are sensitive indicators of climate change, and their retreat represents a warning sign due to their impacts on water supply, biodiversity, and ecosystem stability.
A recent study published in Science Advances by researchers from the University of Wisconsin-Madison, led by Andrew G. Jones, provides new evidence on the glacial history of the Sierra Nevada of California and projects an unprecedented scenario.
Glacial persistence during the Holocene
The Conness and Maclure glaciers maintained continuous ice for more than 11,000 years.
The study shows that the Conness and Maclure glaciers, located near Yosemite National Park, preserved continuous ice cover throughout the Holocene, the interglacial period that began 11,700 years ago.
This means that their projected disappearance in the coming decades would be a novel phenomenon in the planet’s recent history.
“When these glaciers die, we will be the first humans to see ice-free peaks in Yosemite,” stated Jones.
Advanced techniques to reconstruct the glacial past
The researchers used carbon-14 and beryllium-10, elements formed in rocks exposed to cosmic rays, to determine the historical presence of ice. The low concentrations found indicate that the rocks were covered by ice for almost the entire Holocene, blocking the formation of these isotopes.
Additionally, 17 bedrock samples and 55 moraine blocks were collected at the glacier margins, confirming the glacial persistence even during the warmest episodes of the period.
An unprecedented retreat of glaciers driven by humans
The current global warming exceeds the thermal limits recorded in the last millennia.
The research shows that the glacier equilibrium line in California has already surpassed all records since the human settlement in North America was documented.
The East Lyell glacier, the smallest in the area, grew 7,000 years ago, earlier than previously thought, reinforcing the idea that a total disappearance of these ice bodies had never been recorded in the Holocene.
“Anthropogenic climate change is creating an unprecedented scenario in the western U.S.,” the authors conclude.
Implications for science and conservation
The applied methods allow addressing debates on ice-free periods and projecting future climates.
The use of cosmogenic isotopes and numerical modeling confirms their usefulness in reconstructing glacial history and responding to hypotheses based solely on sedimentary records.
These advances allow better understanding of ice dynamics and anticipating the impacts of global warming in mountainous regions.
