A state-commissioned report on effects of rising sea levels from global warming found that two-thirds of the state's most vulnerable coastline and wetlands are in the San Francisco Bay Area.
A map shows nearly half the peninsula under water -- pretty much everything to the east of Highway 101.
Silicon Valley headquarters of Yahoo, Google, Intel and Hewlett-Packard among many others would have to move unless protected by a massive, and costly dike-building project.
Urban coastlines are particularly vulerable because they were expanded by fill in order to add extra real estate.
Groundwater pumping has also settled some areas, placing them below expected sea levels.
The study, from the non-profit research firm the Pacific Institute, says that seawalls and levees could cost $14 billion up front and $1.4 billion a year in maintenance.
The predicted 4.6-foot rise is considerably higher than earlier estimates because of new data from the melting of polar ice sheets, which scientists say is accelerating. Photo by Flickr user star5112.