AN FRANCISCO ENGINEERS recently mapped out a chilling scenario: What will happen if the bay surges over a six-foot seawall protecting the Embarcadero water-front? If an unusually high storm surge breached the structure, water could submerge subway tunnels, knock out utilities, and impact hundreds of thousands of people. Today the risk is low, but climate change will push flooding inland. If sea levels rise by seven feet, which could occur by 2100,
