Havoc to S.F. Bay Possible Due to Big Rise in Seas : Environment: An increase in the ocean level of one meter from global warming could devastate Bay Area, a worst-case scenario asserts.

SAN FRANCISCO —  Rising seas caused by warmth trapped in polluted air could inundate $48 billion worth of property along San Francisco Bay over the next century unless preventive action is taken, a Berkeley research organization estimates in a report released today.

The impact of global warming, the so-called greenhouse effect, projected by the nonprofit Pacific Institute, is a worst-case scenario based on a one-meter rise in sea level from melting land ice and expansion of the oceans themselves as they warm.

Recent research predicting a rise of only about one foot, less than a third of a meter, would reduce the impact predicted by the report, which suggests all of California would have to undertake a massive construction job to preserve its current coastline.

“The cost of protecting against a sea rise of half a meter isn’t that much different from protecting against a full meter,” said Peter H. Gleick, author of the report with Edwin P. Maurer. “Besides, a prediction of a 30-centimeter rise (roughly one foot) by 2050 doesn’t mean the sea would stop (rising) there. That kind of rise is consistent with a full meter by the end of the (21st) century.”

Even at much lower increases of six inches or less, Gleick and Maurer project more frequent severe storms that would lash shoreline property if not inundate it. A storm that today would be considered the worst in a century would happen once a decade if the sea level rises just half a foot, the researchers said.

“A sea-level rise will irrevocably change the nature of San Francisco Bay. It’s a no-win situation,” Gleick said. “Even if we were to build all of the levees and seawalls needed to protect existing development, we would lose vast stretches of wetlands.”

Predictions of massive disruption to coastal zones have usually accompanied projections by most scientists of how the greenhouse effect will nudge average temperatures up by anywhere from four to nine degrees Fahrenheit over the next 100 years.

Scientists at the National Oceanic and Atmospheric Administration and other government and private research agencies think that small but critical warming may have some benefits--increased food production, quicker forest growth and increased fresh water supplies. But it will come at a massive cost of flooding along coastlines, where half of the world’s population lives.

In its study, the Pacific Institute applied those expectations to a specific, known region--San Francisco Bay, which as the nation’s second-largest estuary has a large part of its population living near the water and has particular economic and ecological importance to California.

The most obvious effect is a great expansion of land area subject to floods under highest tide. San Francisco International Airport would be in danger, as would highly developed areas of San Mateo County, including NASA Ames Research Center and Moffett Field Naval Air Station.

Across the bay, Oakland International Airport probably would be swamped, as would large parts of Oakland itself. Treasure Island, an artificial island housing a Navy base in the middle of the bay, would vanish. So, too, would several other military installations, including the Alameda Naval Air Station, Oakland Army Terminal and U.S. Coast Guard Reservation.

Farther north, the Sears Point Raceway and the abandoned Hamilton Air Force Base would be affected. Parts of the cities of Napa, Vallejo and Fairfield could be washed out.

People who avoid flooding from the high tides would not be able to avoid the deterioration of the region’s ground water basins due to sea-water intrusion. Nor would they be likely to escape sharing in the cost of erecting seawalls and levees to shield low-lying areas from the rising ocean.

Gleick and Maurer estimate the cost of building seawalls and levees, or modifying existing ones, at $942 million. Maintaining those defenses, they add, could run as high as $100 million a year.

To minimize the impact of rising seas, the researchers suggest an immediate prohibition of development along the coast and adjacent marshes, tidelands and other wetland areas. Flood insurance programs should be modified or phased out in areas likely to be affected by future flooding, they say.

Even with such adjustments, the dislocation caused by significant sea level change will, over time, be substantial, Gleick and Maurer said.

“Some of the impacts of a sea-level rise may never be quantifiable,” they said. “These include . . . social costs of migration away from affected areas, the psychological pressures of living behind coastal protection in threatened areas (and) the value of lost or altered ecosystems.”

Greenhouse Effect Flood Threat To illustrate the potential problem posed throughout California if the heat trapped in polluted air causes sea level to rise. Berkeley’s Pacific Institute mapped out Bay Area land subject to floods by a one-meter (3.3-foot) increase. This is based on early estimates of rising seas and is considered a worst-case scenario. Some scientists believe global warming may cause a rise of only one foot at most over the next century.