A new study provides a glimpse into the future of Western U.S. snow and the picture is far from rosy: In about 35 to 60 years, mountainous states are projected to be nearly snowless for years at a time if greenhouse gas emissions continue unchecked and climate change does not slow.

Due to rising temperatures, the region has already lost 20 percent of its snowpack since the 1950s. That’s enough water to fill Lake Mead, the nation’s largest human-made reservoir. It stands to lose another half, and possibly more, later this century, from the Rockies to the Sierra Nevada and into the Cascades of the Pacific Northwest, according to a literature synthesis conducted in the study leveraging dozens of peer-reviewed climate model projections.

The current snow situation in the West offers a preview of what the future may hold. Snow water equivalent, or the liquid water from snowpack, is much lower than normal in much of the Western United States. Snow cover across the nation is only at 6 percent — the lowest since records began in 2003.

Decades ahead, the “potential for persistent low-to-no snow to disrupt the [Western U.S.] water system is substantial, potentially even catastrophic,” the study’s authors write.

Published in Nature Reviews Earth and Environment in October, the paper provides an overview of how Western snowpack has changed and what it will look like over the course of this century.

In addition to the 20 percent loss, snowpack is peaking and melting off earlier in the year and is expected to continue on that track. Atmospheric rivers are also warming and dropping more rain than snow, which increases flood risk.

The demands of a warmer atmosphere are already translating into water stress. Although this past year was not a “low snow” year for California, much less snowmelt made it to reservoirs because of an unusually warm spring.