Understanding the full history of the glacier’s extent can help scientists better understand the significance of glacier retreat measured today. Along these lines, a recent study published in the journal Science reveals a new technique that allows researchers to determine the extent of historical glaciers and assess how little ice cover exists in the Andes today. Their findings show the glacier is retreating like never before.
To conduct their work, the researchers climbed four glacial mountain ranges in Colombia, Peru and Bolivia and chiseled away bedrock samples. The samples were then analyzed using a new method called “cosmogenic isotope analysis.”
When highly charged particles from space, called cosmic rays, enter our atmosphere, they create a chain reaction by interacting with other atomic particles in the air. As they bounce around, they create secondary particles with less energy. This cascade of interactions eventually causes neutrons to hit the Earth’s surface. When a glacier retreats, the bedrock beneath it is exposed to these neutrons.
“As this reaction occurs, the byproduct is these new cosmogenic nuclides that form in the rock. The longer the rock is exposed to the atmosphere, the more nuclides are formed,” says Nicholas Young, a paleoclimatologist at the Columbia Climatology Institute. explain. Nuclides are a unique class of atoms. However, these nuclides cannot form without direct exposure to the atmosphere. If bedrock is covered in ice and snow, the cosmic radiation needed to create nuclides is blocked. “Once the ice recedes and exposes this new bedrock, we say the ‘cosmic clock’ has started. It is now able to accumulate cosmic nuclides,” Yang said.
From each gravel sample, the researchers were able to determine how long the rock had been exposed to the atmosphere. Specifically, they looked at concentrations of beryllium-10 and carbon-14 nuclides that accumulated in rocks at the edge of the glacier. Because this bedrock is recently exposed rock, the high concentration of nuclides suggests it must have been discovered in the past, but the lack of nuclides suggests an ice-covered history.
“What’s unique about this study is that they basically didn’t measure anything,” Yang continued. Because there were almost no nuclides in the rock, the researchers concluded that the bedrock must have been covered in ice for thousands of years, long enough for any nuclides formed in the distant past to decay. “You can say with great confidence that this bedrock has probably never been exposed to the atmosphere, at least in recent geological time,” Yang said.
The study concluded that Andean glaciers were the smallest in 11,700 years. That’s about the length of our current geological epoch known as the Holocene, which began after the last ice age and is the era in which all human history took place. In recent decades, advances in anthropogenic climate change have brought temperatures higher, melting ice and limiting freezing. While these impacts are known to cause glacier shrinkage, the severity of this glacier retreat and its effects have not been clearly established to date.
“What is certain now is that most mountain glaciers and ice sheets are retreating to some extent,” Yang said. “The purpose of this study is to understand the severity of the current recession – how unprecedented is it?”
future impact
Throughout the Holocene, there were periods of glacial growth and retreat, with most glaciers experiencing a glacial minimum long before the early to mid-Holocene. Glaciers in the Northern Hemisphere, although currently shrinking, have not yet reached Holocene minimums like the tropical glaciers in this study. However, the conclusions about these Andean glaciers may be a sign of what will happen to glaciers around the world as anthropogenic warming continues.
If glaciers around the world continue to shrink at the unprecedented levels already achieved by tropical glaciers, there will be local and global consequences. “These types of glaciers will contribute to sea level rise in the short term, but at least on human timescales, the bigger concern is water availability,” Yang said.
Many communities rely on mountain glaciers for water supplies, which have proven to be a safe source of water over hundreds of years. The regular cycle of snowfall to glacier melt that supports watersheds in mountain communities is threatened by extreme glacier retreat. Paola Moschella Miloslavich, director of glacier research at Peru’s National Institute of Glaciers and Mountain Ecosystems, tells GlacierHub about some of the ways glacier retreat is already affecting mountain communities. “The most significant impacts are reduced water availability, particularly during the dry season, and reduced water quality due to acidic drainage of recently exposed bedrock, which affects agriculture and livestock,” she said.
The study found that the glaciers’ extremely low ice cover has harmed the livelihoods of mountain communities, who are now at risk of drought and poor water quality. “Reducing global greenhouse gas emissions is essential to slow the rate of glacier retreat and maintain their ecosystem services,” Moschela Miloslavic said. Reducing land-use changes that reduce the surface area of mountain ecosystems is also necessary, and It must be combined with the restoration of degraded ecosystems. “All these measures require a framework of inter-agency collaboration at different scales and incorporate the knowledge of local communities,” she added.
Mountain communities are already experiencing the direct impacts of climate change and glacier retreat. However, if this study shows the progress of anthropogenic warming, they won’t be the last. This study paints a shocking picture of the fragile state of our planet from inside the rocks at the edge of Andean glaciers.
