About a quarter of the glaciers in the contiguous United States have disappeared since the mid-20th century, a new study found. The study was published Monday in the Proceedings of the National Academy of Sciences, the San Francisco Chronicle and WTAE reported.

The lower 48 states now have 1,331 glaciers, WTAE reported. The total volume of glacier ice has fallen by 33% compared with studies from the 1950s to 1980s. Total glacier area has fallen by 35%, the Chronicle reported. The researchers combined old U.S. Geological Survey records with modern aerial and satellite images.

Glaciers are shrinking by about 8% each decade in the western U.S., WTAE reported. Six western states have glaciers, and Washington has by far the most.

California's Sierra Nevada has been hit hard. The number of glaciers there fell from 94 to 64 since the 1970s, and glacier volume fell 77%, the Chronicle reported. The glaciers in Washington's Cascades have done better, but they have still shrunk.

"It dawns on me that in a few decades no one will be reading my papers because there'll be no glaciers to worry about," said lead author Andrew G. Fountain of Portland State University. "The glaciers will be gone," the Chronicle reported.

Glacier melt is an important source of water in hot, dry summers. The newest data in the study is mostly from 2013 to 2019, so more melting has likely happened since, the Chronicle noted.

Some new glaciers appeared in the count, the Chronicle noted. But most were old glaciers that broke apart as they melted, not new ice.

What we know: The lower 48 states have lost about a quarter of their glaciers and about a third of their glacier ice.
What we don't: How much more ice has melted since the latest data, and how fast the rest will go.