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When powerful storms pummel the coast, strong waves erode the rock and haul beach sand out to sea. In some parts of Southern California, strong waves have already stripped some beaches, and if climate change continues on its present course, the situation will get much worse. By 2100, scientists predict that many of Southern California’s iconic beaches and top surfing spots, from Coronado Beach in San Diego to Will Rogers State Beach in Los Angeles and beyond, will be washed away.

Beaches go through cycles of erosion and replenishment. In Southern California, winter storms and heavy surf pull sand away, and summer waves and sediment from rivers gradually bring it back. But according to a new study, between 31 and 67 percent of the region’s beaches will be irrevocably lost by the end of the century.

To come to this conclusion, a team of geologists led by University of Illinois civil engineer Sean Vitousek modeled how the beaches will be affected by various climate change scenarios, including sea level rise and changing storm patterns and wave conditions.

“These model results show that if sea levels get as high as expected, it means pretty serious consequences for the coastal zone,” says Vitousek.

As the planet warms, the melting of massive quantities of ice in Greenland, Antarctica, and elsewhere will, along with other processes, lead to between 0.9 and two meters of sea level rise, according to the Intergovernmental Panel on Climate Change.

For California, that’s more than enough to inundate narrow beaches, flood coastal communities, and damage property. The state’s coastal and ocean economy, mostly based on ports, harbors, and tourism, is worth up to US $45-billion annually, and much of that economy will be at risk should these beaches vanish.

“Beaches and coastal property are the most valuable assets California has,” says Judith Kildow, director of the National Ocean Economics Program at the Middlebury Institute of International Studies at Monterey.

Vitousek says that even with a concerted effort to mitigate climate change, some erosion will be inevitable. The researchers recommend management efforts and beach nourishment to dredge sand farther out and bring it back, though both require ongoing maintenance. In the meantime, coastal residents will have to contend with the controversial question of whether to armor the coast and hold the line, at a considerable expense, or give in to the rising water.

In the long term, gradually retreating from the coast may be the cheapest way to go. In some areas, despite millions of dollars of development, the shoreline will eventually move in. “It’s going to happen, and all the nourishment and armoring in the world won’t save it,” says Gary Griggs, a geologist at the University of California, Santa Cruz.

Californians will have to start planning for this future—and deciding which beaches are their highest priority. They can’t save them all, Griggs says.