Chunks of ice float on Mendenhall Lake in front of the Mendenhall Glacier in May 2022, in Juneau, Alaska. Becky Bohrer/Associated Press, file

A global loss of glaciers resulting in rising sea levels is far more substantial than previously thought, a study published Thursday in the journal Science reveals.

Scientists from around the world – including one from Carnegie Mellon University – used what is called a glacier evolution model, inputting different temperatures and precipitation levels into a coding program to glean context about the worst- and best-case scenarios for the world’s glaciers. The study was partly funded by NASA.

Given current warming trends, the planet’s glaciers are on track to lose at least a quarter of their mass by 2100, and that is a best-case scenario that would involve “considerably more (climate) targets set by other countries, now,” said David Rounce, an assistant professor of civil and environmental engineering at CMU.

Not just a scientific exercise, the modeling could predict a massive impact on iconic places on the map like the Alps and the Andes mountain ranges and resources such as freshwater supplies to communities near them.

“Glaciers are like slow-moving rivers, so modeling their flow is really important,” Rounce said.

Rounce and his colleagues’ model predicted the world would lose between 50% and 83% of all glaciers by 2100 and see the sea level rise by 3.5 to 6 inches.

One of the keys is temperature changes that scientists see triggered by greenhouse gasses, as they trap heat and intensify storms. If the global temperature increases 4 degrees Celsius above the average set before the arrival of heavy industry in the 20th century, the model predicts nearly half of all glacial mass will be lost.

The scientists also measured the number of glaciers that would be lost. They examined each condition with a 1.5-degree Celsius global temperature increase as well as a 4-degree Celsius temperature increase (a range of approximately 35 to 40 degrees Fahrenheit).

An increase of 1.5 degrees Celsius might not seem like much, but climate scientists are calling it catastrophic.

While numerous efforts are underway to curb the production of greenhouse gasses, a November New Yorker article by science journalist Elizabeth Kolbert found that even when countries pledge carbon neutrality this does not always translate to direct action.

“Eighty-three percent is a shocker,” said Bryan Mark, a professor of geography at Ohio State University who has studied glacial science for decades in the Andes and other mountain environments.

“We would lose the Alps, the Andes, and Glacier National Park would become Glacier Grave National Park,” said Mark, who was not involved in the present research.

Glaciers are also important freshwater resources for numerous communities who live near them, such as those in the Himalayas and the Andes Mountains. “As we remove freshwater storage, we’ll have to think about other ways to store water, like dams,” Mark said.

But because of tectonic plate activity, the Himalayas are prone to earthquakes, which, if the glacier melted and a subsequent dam was built, could lead to what is called a “glacial lake outburst flood.”

Millions of coastal residents will be affected by sea level rise. “The surface of the Earth is 71% ocean,” Mark said. “Three-point-five inches is a huge amount of water.”

And the population won’t be affected by climate change equally – research, and past disasters such as Hurricane Katrina have shown that people of color and people of lower incomes are impacted disproportionately by the worst consequences of climate change, such as flooding, heat waves, and drought.

Glaciers act as insulators for the Earth’s exposed and vulnerable crust. Fewer glaciers to reflect UV radiation means more rock will be exposed and will absorb more heat, accelerating the warming of the glaciers that did survive.

The researchers’ modeling study did not include ice sheets: massive swaths of ice that store much of the world’s freshwater – the Greenland ice sheet being one example.

Glacial melt has led to an unprecedented situation that scientists don’t have references for. “What’s happening now is happening so fast that we can’t compare it to anything in the past,” Mark said. “We call it a no-analog situation. Warming is accelerated, so we have had a lot of warming dynamics to ice loss that previous models may not have accurately accounted for.”

That’s what makes Rounce’s study important. Mark called it “a wake-up call.”

Mark said that, although he has studied glaciers for decades, he still finds himself shocked to see the changes in person.

He has revisited sites where he walked on glaciers as a graduate student and found the landscape drastically altered – where the valley of a glacier once butted up against a lake, now the glacier is nearly half a mile up the hill. Another used to have a rock peeking out of its center. “Now it’s a 100-meter cliff,” he said.

And glaciers, for many communities, hold cultural significance. Mark, who studied and lived in Peru, said the Huaytapallana glacier is home to worship ceremonies led by shamans and people who bring gifts to apus, or the mountain gods, and pray for a glacier’s longevity. As glaciers are lost, “cultural history is lost” too, he said.