Glaciers in the Sierra Nevada have decreased dramatically since the beginning of the twentieth century. In the Trinity Alps, one of two glaciers has recently disappeared, and the other has almost completely melted.

Glaciers provide the most visible evidence of climate change. A glacier gains mass from winter snowfall and loses mass when warmer spring and summer temperatures melt ice and snow. Globally, glaciers have shrunk over the twentieth century due to a warming climate. For more information, download the Glacier Change chapter. 

Graph shows the change in the area of seven glaciers in the Sierra Nevada as a fraction of its size in 1903.

Source: Basagic and Fountain, 2011
(updated 2021 H. Basagic, unpublished data)

• The surface area of seven of the largest Sierra Nevada glaciers decreased dramatically during the past century. By 2021, they lost an average of about 75 percent of their 1903 area.

• Greater losses have been observed in the Trinity Alps, where two glaciers lost about 80 percent of their area between 1885 and 1994 (graph not shown). During the 2012 to 2016 drought, two snowfields completely melted, Salmon Glacier disappeared entirely, and Grizzly Glacier broke apart into large ice blocks. By 2021, the Grizzly Glacier lost so much of its area such that it may no longer be considered a glacier.

• Glaciers act as frozen reservoirs of snow. Glacial shrinkage results in earlier snowmelt runoff.

• Glacial runoff provides critical cold freshwater habitat for many aquatic species, and water for vegetation during the drier summer months. Cold glacial waters flow into streams and rivers where Chinook salmon populations reproduce and grow.

• Water from melting glaciers contributes to global sea level rise.

• Glaciers are melting largely due to increasing air temperatures. Notably, unprecedented high summer temperatures and low winter precipitation during the 2012-2016 drought and the return of drought conditions in 2020 and 2021 led to the catastrophic glacial loss in the Trinity Alps.

• Local topographic features, such as steep mountain walls, affect how glaciers respond to sun and wind exposure.

The Lyell Glacier in the Sierra Nevada has been steadily shrinking since it was first mapped and photographed in 1883. Melting has accelerated rapidly in recent years, especially during the drought that began in 2012.

Credit: National Park Service

• National Park Service, Yosemite National Park, Glaciers
• Portland State University, Glaciers of the American West
• World Glacier Monitoring Service, Global Glacier State