As the water level in the seas and oceans around the world continues to rise, there are many coastal areas that are at risk. A new study by researchers from the U.S. Geological Survey (USGS) showed that California is definitely one of those places, and that the golden state could find anywhere between a third and two-thirds of its southern beaches completely eroded by 2100.

“Using a newly-developed computer model called ‘CoSMoS-COAST’ (Coastal Storm Modeling System – Coastal One-line Assimilated Simulation Tool) scientists predict that with limited human intervention, 31 to 67 percent of Southern California beaches may become completely eroded (up to existing coastal infrastructure or sea-cliffs) by the year 2100 under scenarios of sea-level rise of one to two meters,” a statement about the study on the USGS website said Monday.

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This prediction is in direct contrast to the historical trend in Southern California, where the beaches have become larger over time, due to human activity since the 1930s to enlarge the beaches. According to the study’s model, almost all the beaches in the region will suffer some amount of erosion in the coming decades.

Sean Vitousek, lead author of the study, which he conducted while he was a post-doctoral fellow at USGS, and now a professor at the University of Illinois at Chicago, said in the statement: “Beaches are perhaps the most iconic feature of California, and the potential for losing this identity is real. The effect of California losing its beaches is not just a matter of affecting the tourism economy. Losing the protecting swath of beach sand between us and the pounding surf exposes critical infrastructure, businesses and homes to damage. Beaches are natural resources, and it is likely that human management efforts must increase in order to preserve them.”

The movement of sand both along and across beaches, caused by longshore and cross-shore currents respectively, is accounted for by the CoSMoS-COAST model, which also uses historical positions of shorelines — as well as data about changes to beaches in response to waves and climate phenomena like El Niño — to provide reliable forecasts of coastline changes.

The researchers are confident in the predictions by the forecast using the model, especially because it accurately predicted the shoreline changes in the region from 1995 to 2010. The current forecast is for the 2010-2100 period.

CaliforniaErosionModel An example of the shoreline data for La Jolla Shores, used in the CoSMoS-COAST model. The many squiggly colored lines indicate the changing location of the shoreline through time. Basemaps were taken from Google Earth. Photo: Sean Vitousek, U.S. Geological Survey

California Coastal Commission Executive Director John Ainsworth said in the statement: “The prospect of losing so many our beaches in Southern California to sea level rise is frankly unacceptable. The beaches are our public parks and economic heart and soul of our coastal communities. We must do everything we can to ensure that as much of the iconic California coast is preserved for future generations.”

An unedited but peer-reviewed version of the study, titled “A model integrating longshore and cross-shore processes for predicting long-term shoreline response to climate change,” was published online in the Journal of Geophysical Research.

Read: How Climate Change Is Impacting Sea Level Rise

The change in sea levels is not a new phenomenon, and has happened numerous times in the history of Earth. However, the rate at which it has been rising recently is increasing and a cause for concern. According to data from the National Oceanic and Atmospheric Administration (NOAA), the global sea level was 2.6 inches higher in 2014 than the 1993 average, and sea levels continue to rise at about an eighth of an inch every year, on average. And this rise is caused by expanding ocean water as it warms, as well as increased melting of ice contained in glaciers and ice sheets.

The ramifications for both the U.S. and the world are potentially dire. “With continued ocean and atmospheric warming, sea levels will likely rise for many centuries at rates higher than that of the current century.  In the United States, almost 40 percent of the population lives in relatively high-population-density coastal areas, where sea level plays a role in flooding, shoreline erosion, and hazards from storms. Globally, eight of the world's 10 largest cities are near a coast, according to the U.N. Atlas of the Oceans,” the NOAA said.