Report Warns of Potential for Coastal Flooding : Environment: Ocean off Southern California has warmed about 1 1/2 degrees since 1950, study says. Some scientists say the trend may be linked to rising sea level.

Southern California’s ocean water has warmed slightly during the past four decades, causing a minuscule rise in sea level each year--a trend that concerns some scientists who say it could one day lead to coastal flooding, according to a report in a scientific journal to be released today.

The local ocean surface waters since 1950 have gradually warmed by about 1 1/2 degrees Fahrenheit, which has caused the seawater to slowly expand and rise by 1 1/2 inches, said Dean Roemmich, author of the study in Science.

“The ocean is indeed changing here,” said Roemmich, an associate professor of oceanography at the Scripps Institution of Oceanography. “This translates to some degree of concern as to what happens in the next 20 years.”

The total sea level rise is so small that it poses no immediate threat to California’s beaches and structures along the coast, Roemmich said. It is not known what impact--if any--the warming or the sea level rise will have on marine ecology.

The global sea level has been rising at a rate of about 2 millimeters--just under a tenth of an inch--each year, which scientists believe could result from several factors, including the greenhouse effect, melting glaciers, and changes in the shape and volume of ocean basins.

Global warming, some experts say, is caused by the emission of carbon dioxide and other gases from cars and industry. These gases collect in the atmosphere and act like a greenhouse, trapping heat from the sun.

But scientists have not determined how much of the ocean’s warming is because of the greenhouse effect or other culprits. Nor does the study indicate that the warming of local waters is caused by the greenhouse effect, Roemmich and others say.

“To make the leap that it’s proof of global warming is too big a leap,” said Bruce Parker, a principal investigator for the National Oceanic and Atmospheric Administration in Maryland. “It’s very difficult to separate out the potential causes.”

But others say the findings are cause for concern, particularly if the warming trend quickens.

“If it does accelerate, we are in serious trouble. Even a 10-centimeter (four-inch) rise is nothing to laugh at” and could trigger coastal flooding and other environmental problems, said Robert Watts, a professor of engineering at Tulane University who studies climate change. Roemmich examined results of sampling along the coast for the last 42 years from Del Mar to Point Conception, extending near the shore to 310 miles offshore. Roemmich found a steady increase in the warming of the top 325 feet of ocean, with the effect apparent but lessening down to 1,000 feet.

“I can’t conclude (from the data) whether this is part of the natural climate or it’s induced by human activity. If it’s human activity, then I suspect the rate of rise and warming could accelerate in the next 20 years,” Roemmich said. “If the sea level increases, you worry about coastal flooding.”