The study\u2019s authors, who also included scientists from other universities and the National Park Service, wrote that California\u2019s glaciers are thought to have reached their maximum extent about 30,000 years ago, and that the research indicates \u201ca future glacier-free Sierra Nevada is unprecedented in human history\u201d since people arrived in the Americas from Asia approximately 20,000 years ago.<\/p>\n
Glaciers are rapidly shrinking around the world, from the Himalayas<\/a> to the Andes<\/a>, as temperatures are pushed higher by the use of fossil fuels and rising greenhouse gas levels.<\/p>\n East Lyell glacier in Yosemite National Park in September 1883 (A) and in September 2022 (B).<\/p>\n Jones said many of the glaciers he and his colleagues study in California have lost an estimated 70% to 90% of their ice since the late 1800s.<\/p>\n Photographs and written accounts show how much the Sierra\u2019s glaciers have retreated.<\/p>\n In one expedition in 1872, John Muir used wooden stakes to measure the movement<\/a> of the Maclure glacier. In an article<\/a>, Muir wrote that as he examined another \u201chuge snow-bank, four or five hundred yards in length, by half a mile in width,\u201d he saw masses of rocks and dirt that had been pushed by the moving ice, and \u201cI shouted \u2018A living glacier!\u2019\u201d<\/p>\n In 1883, when Israel Russell photographed the Lyell glacier<\/a> in Yosemite for the U.S. Geological Survey, it was a single ice mass. Now, it\u2019s split into east and west portions, and the ice has stopped moving.<\/p>\n The East Lyell glacier, which backpackers see while traveling along the John Muir Trail, has lost an estimated 95% of its volume since the late 1800s, the researchers said. <\/p>\n In the Sierra Nevada, the snow that blankets the rugged landscape each winter melts and gushes in meadows, streams and rivers, nourishing alpine ecosystems and filling reservoirs. <\/p>\n When the snowpack is gone by late summer, the glaciers that remain, often in the shadows of peaks, release meltwater that keeps streams flowing at the driest times of year.<\/p>\n This water from glaciers serves as a \u201cstabilizing force\u201d that can sustain mountain streams through droughts, Jones said. But he added that this water eventually will go away as the glaciers continue to retreat, and that some streams, like those that feed the Tuolumne River in Yosemite, will run dry at times.<\/p>\n \u201cUltimately, it\u2019s telling us that we\u2019ve left the bounds of so-called normal,\u201d he said. \u201cWe\u2019re crossing the line in the sand from what glaciers have done, for basically all of human recorded history.\u201d<\/p>\n East Lyell glacier in Yosemite National Park on June 24, 2021.<\/p>\n (Ian James \/ Los Angeles Times)<\/p>\n The Sierra Nevada\u2019s snowpack is also seeing the effects of rising temperatures: Average snowlines are creeping higher in the mountains<\/a>. <\/p>\n In the latest study, the scientists note that summer temperatures in California have warmed about 3.6 degrees Fahrenheit over the last century, and they describe mountain glaciers as \u201csensitive climate indicators.\u201d<\/p>\n They visited glaciers and collected rock samples on research trips in 2018, 2021 and 2023.<\/p>\n \u201cGlaciers are touchstones between the past and the present, and it\u2019s just so visceral when you can see how it used to be and how it is today,\u201d Jones said.<\/p>\n <\/p>\n
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