SAN FRANCISCO (Reuters) - California Gov. Arnold Schwarzenegger on Friday ordered preparations for rising sea levels from global warming, a startling prospect for the most populous U.S. state with a Pacific Ocean coastline stretching more than 800 miles.

Recorded sea levels rose 7 inches during the 20th century in San Francisco, Schwarzenegger said in the executive order for study of how much more the sea could rise, what other consequences of global warming were coming and how the state should react.

California is considered the environmental vanguard of government in the United States, with its own standards for car pollution and a law to cut emissions of carbon dioxide, the main gas contributing to global warming.

“The longer that California delays planning and adapting to sea level rise the more expensive and difficult adaptation will be,” Schwarzenegger said, ordering a report by the end of 2010.