The Brief

Glaciers in California’s mountains are disappearing fast and will likely be gone by the end of the century. Geologists found that these glaciers have been in place since before humans came to the Americas. This means there is no precedent in the last 20,000 years for their disappearance.

The new research challenges a previous assumption that California’s glaciers had waxed and waned into disappearance since the end of the last glacial period, offering a new understanding of their history.

Glaciers offer a touchstone — something we can literally hike to and touch — providing a link between our past and present.

“The reason this work is important is because climate change feels abstract and nebulous,” said Andrew Jones, a Ph.D. candidate at the University of Wisconsin-Madison and lead author on a study published Wednesday in Science Advances. “You hear about two degrees Celsius of warming. To most people, that’s just an imperceivable difference on their home thermostat. But our findings here are tangible.”

To accompany the paper, Jones and his co-authors released comparative photographs showing before and after pictures. For instance, in the late 1880s, when John Muir was studying glacial flow with wooden stakes, the East Lyell Glacier in Yosemite covered a broad sweep of the mountainside. Today, it is just a few blobs clinging on in the hollows.

Maclure Glacier in Yosemite National Park.

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Courtesy Andrew Jones

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This glacier will be familiar to anyone who has hiked south from Tuolumne Meadows toward Donahue Pass. Backpackers who love the Sierra Nevada may be likewise familiar with other glaciers evaluated by the research team: Maclure, Conness and Palisade.

The researchers, however, had to access these glaciers without the benefit of trails. The fieldwork was grueling, Jones admitted with a laugh: “Man, the hiking was really difficult, honestly.”

The research team traversed glacial moraines — large deposits of rock out in front of glaciers — places that had been covered by ice until a few decades ago. From there, they collected samples of bedrock just below glaciers to determine, through isotopes, how long it had been since that rock was last exposed to sunlight.

“The [moraines] are very loose, very treacherous. You step on a boulder and it slides,” said Jones. “You’re like, ‘Oh that’s not good.’”

Jones also said he had to laugh at the effort he and other members of the research team put into packing ultralight, bare bones gear. They did things like snap toothbrushes in half to save a few ounces, only to then carry out backpacks full of pounds of rock for testing.

“It was all the sacrifice of ultralight for none of the benefit,” he said.

To determine whether California’s glaciers had disappeared and reemerged since the last glacial maximum, the team used carbon-beryllium isotopes to evaluate those recently exposed rocks. Jones uses a battery analogy to explain. When the ice is gone and rock is exposed, the sun can “charge up” the rock. When the glacier comes back, the charge slowly recedes. But they found no “charge” at all in the glaciers tested in and around Yosemite.

“That tells us that rock has not seen the light of day for a very, very long time.” They estimate at least 10,000 years, probably 30,000 years. That’s before humans began living on this continent.

This finding contrasts with the history of glaciers in the Swiss Alps, which have expanded, shrunk, expanded, and then, with global heating, begun to shrink again.

Many of the glaciers in the Sierra Nevada have shrunk so much that they no longer flow or move, which geologists consider “alive.” A slow slide downhill is a hallmark of normal glacial behavior — and it results in beautiful glacial carving of rock — but to do that, it has to be of a certain thickness. Many of California’s glaciers are now too small and thin.

When the Sierra Nevada glaciers are all gone, as projected in 2100, the generation of kids living now will be the first humans ever to see the rocks below.

Glacial loss feels like emotional loss for many who love the mountains. But here, amid the sadness, there is room for perspective and hope.

Mountain glaciers are more sensitive to climate signals than other indicators, like the polar ice sheets. Changing the trend of an ice sheet is a huge undertaking — like turning a colossal ship. A glacier, like Lyell, is comparatively a small boat — one that can turn quickly.

“Our decisions really do matter in how many glaciers survive,” Jones said.

If we succeed in bringing down the concentration of warming gases in our atmosphere closer to levels we saw in the late 1980s (350 parts per million), glaciers globally would have a good shot at stabilizing, perhaps even starting to grow again. Just as their loss has heralded a heating planet, one that is suffering as if from a fever, their reappearance one day could be an early signal of a planet returning to health.