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At least $100 billion worth of homes, businesses, power plants, ports, and airports in California could be at risk from extreme coastal storms by 2010, estimates a new assessment of California鈥檚 vulnerability to rise in sea levels.

Some 480,000 people living in coastal counties could be affected, according to the study.

The report, released Wednesday, is part of a larger state effort to assess the full spectrum of risks it faces from global warming and to begin to outline adaptation strategies that planners should consider. It鈥檚 the latest in a growing number of efforts nationwide to figure out what needs to be done along the heavily populated coasts to prepare for rising sea levels.

The study represents 鈥渁n incredible effort to pull together an enormous amount of data,鈥� says Reinhard Flick, a research associate at the Scripps Institution of Oceanography in La Jolla, Calif., and an oceanographer with the California Department of Boating and Waterways. 鈥淚t will be very useful going forward as a reference.鈥�

The new assessment comes at a time when the National Research Council in Washington has called on climate scientists in the United States to place increased focus on research to support adaptation efforts.

Globally, recent sea level rise has been outpacing projections made by the Intergovernmental Panel on Climate Change in 2007, several climate researchers have said. At a meeting in Copenhagen, Denmark this week, researchers suggested that sea levels could rise by 1 meter (3.3 feet) or more by 2100, the result of global warming鈥檚 direct heating of the ocean as well as glaciers melting in Greenland and Antarctica.

Who鈥檚 most vulnerable?
For the California study, researchers at the Pacific Institute, an environmental policy research organization in Oakland, Calif., asked the question: With a 1.4-meter sea level rise, who and what would be affected by a 100-year coastal storm at today鈥檚 population levels?

What emerges is a picture of a coastal state that may not carry the heaviest risk given California鈥檚 population, area, or wealth. And with a 2,000-mile coastline 鈥� once the kinks and bends get ironed out 鈥� the likelihood of a single 100-year storm slamming the entire coast all at once is pretty slim.

Instead, the study presents a picture of an adaptation challenge that changes drastically with location and requires a full palette of measures 鈥� from building or strengthening sea walls and levees to protecting land inland of wetlands so that聽 the wetlands have room to migrate as sea level rises.

The counties with the heaviest risk to people include Orange County in southern California and San Mateo County in the Bay Area.

Nor is the risk largely borne by wealthy movie stars with expensive homes lining Malibu鈥檚 beaches.

Lead author Matthew Heberger says he expected that the hardest-hit segment of society 鈥渨as going to be a lot of rich white folks.鈥� In some counties, that was true. But not for others. Contra Costa County on San Francisco Bay, for instance, has significant low-income minority and immigrant populations at risk, he says. Formal studies and past experience indicate that low incomes and language barriers undercut residents鈥� abilities to make their homes flood resistant or to take full advantage of emergency services.

Also at risk are power plants that dot the coast, representing a combined generating capacity of more than 10,000 megawatts. So are Oakland鈥檚 and San Francisco鈥檚 airports.

The study estimates that building or shoring up levees and sea walls to protect such assets along the coast represents a $14 billion investment, with an annual maintenance bill of $1.5 billion a year.

The chance of a really big storm
Although the benchmark is a 100-year storm, that鈥檚 only an average; such storms can strike more frequently, the study points out.

Statistically, during the lifetime of a typical mortgage, there鈥檚 a 25 percent chance that one of these storms will hit. That likelihood rises for structures such as rail lines, bridges, roads, or power plants, which typically last far longer than 30 years.

And the concept of a 100-year storm itself is fuzzy, Dr. Flick cautions. Weather records in California don鈥檛 go back far enough to allow researchers to confidently say what a once-in-a-100-year coastal storm looks like.

Instead, he suggests, the study鈥檚 storm benchmark should be viewed qualitatively as 鈥渁 really big event,鈥� akin to the storms that pounded the coast during the 1982-83 El Nino or the 1988 Martin Luther King Day storm off Los Angeles.

Still, the report begins to allow planners to ask focused questions about adaptation, says Heather Cooley, one of the study鈥檚 authors. And it should serve as a guide for the more-detailed studies that will inform local adaptation decisions.