Americans Alive Today May Become The First People Ever To See Ice-Free Peaks Of Yosemite

Within just 75 years, the glaciers of California’s Sierra Nevada are likely to have melted away, exposing the rocky parts of the mountains for the first time since the Ice Age. When that happens, people alive today may witness something no human has ever seen before: Yosemite’s peaks stripped bare of ice.

The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.

In a new study, scientists have concluded that the largest glaciers in the Sierra Nevada mountain range in the Western US have persisted through the current geological epoch, the Holocene, meaning they haven’t fully disappeared at any point in the past 11,700 years.

That means they survived every warm spell since the last Ice Age, never thawing completely – until now.

The team worked this out by taking samples of newly exposed bedrock from four of the largest glaciers in the Sierra Nevada: the Conness, Maclure, Lyell, and Palisade glaciers. Back in the lab, they examined the rock for concentrations of radioactive isotopes of carbon and beryllium that are produced by cosmic rays.

The analysis revealed that the rock near the two biggest glaciers, one in Yosemite National Park and another near the park border, had been shielded from cosmic radiation for at least 11,700 years, which means it had been hidden under ice all that time.

This is likely to be a conservative estimate, though. The study notes that a wider glacial history indicates that “California’s glaciers reached their Last Glacial Maximum positions as early as 30,000 years ago.” 

There’s a long and winding debate about when humans first populated the Americas, although most estimates suggest it was sometime around 20,000 years ago. Since the glaciers of the Sierra Nevada were probably there as far back as 30,000 years ago, this would suggest that people have never seen ice-free peaks in Yosemite.

But that’s set to change. Climate change is thawing the world’s glaciers are a startling rate, and California’s glaciers are no different. An estimated 75 percent of Sierra Nevada’s glaciers have disappeared since the 19th century, when early surveyors first documented them. Across the western United States, glaciologists project near-total disappearance by the end of this century under most climate scenarios.

The loss could upend ecosystems, water supplies, and downstream, yet it will also mark a moment of geological firsts, revealing a Sierra Nevada whose naked summits have never before been seen by human eyes.

"It means that when these glaciers die off, we will be the first humans to see ice-free peaks in Yosemite," Andrew Jones, lead study author and a paleoclimate expert at the University of Wisconsin-Madison, told the Los Angeles Times. 

The study is published in the journal Science Advances.