Governor Arnold Schwarzenegger and Google unveiled a map of California's climate-changed future on Wednesday, part of the most populous U.S. state's first steps in planning to adapt to inevitable global warming.

California leads the United States in its legal mandate to cut greenhouse gases that warm the planet, from auto mileage standards adopted by the rest of the nation to green building codes.

But the state also is planning what to do about warming that it thinks is impossible to stop. Some $2.5 trillion of property and assets are threatened by climate change, Schwarzenegger said, citing a University of California study.

Nearly half a million Californians are at risk from rising sea levels, while a longer dry season has worsened the fire season and a smaller winter snowpack is affecting water supplies, said the state's first adaptation report, released on Wednesday.

This is illustrated in add-ons to a Google Earth map also unveiled by the state on Wednesday.

On the map, the edges of San Francisco Bay appear colored to show the devastating effects of sea level rises of up to 150 cm (60 inches). All of San Francisco International Airport would be under water.

Other add-ons show snow pack decreases since the 1950s and projected through the end of the century, temperature change, and growing fire risks. They appear under Visualization Tools on the CalAdapt website

Schwarzenegger argued in an animated video simulating a flight over California that cutting carbon dioxide emissions would not be enough.

We must also be prepared for some continued climate change, which is now inevitable, he said.

The governor introduced the video, as well as a new panel to advise on adaptation priorities and an adaptation strategy report, on man-made Treasure Island in San Francisco Bay -- which could be under water in a century as sea levels rise, he said.

(Editing by Eric Walsh)