Proponents hope the first-in-the-nation global warming regulations proposed Monday will encourage similar steps in other states, though automakers have promised to sue over standards they say should be set only by the federal government.
The proposed regulations stem from a law signed by former Gov. Gray Davis in 2002 that requires the California Air Resources Board to set emission standards this year to limit carbon dioxide and other greenhouse gases.
Backers of the law say the state's 23 million cars, trucks and buses produce 40 percent of the greenhouses gases in California that contribute to global warming. Though many scientists believe carbon dioxide, the leading greenhouse gas, is associated with increasing temperatures, others are skeptical of global warming theories.
Carbon dioxide is the product of combustion, so it can't be controlled with filters like other vehicle emissions that cause smog and pollution. To limit the carbon dioxide and greenhouse gases, automakers would have to make vehicle engines that burn less fuel.
The board's staff concluded automakers have the technology to cut emissions 23 percent by 2011 and nearly 30 percent by 2014.
The staff estimated the average cost of meeting the first phase of the new emissions requirements, for model years 2009 through 2011, would add $241 to the cost of a passenger car and $326 to the sticker price of a large pickup or sport utility vehicle.
Stricter regulations for model years 2012 through 2014 would add an average $539 and $851, respectively, the board said. Monday's estimates are lower than costs previewed last week by board chairman Alan C. Lloyd, and were subject to last-minute revisions by the board's staff, said spokesman Jerry Martin.
The Alliance of Automobile Manufacturers has promised to challenge the law in federal court, and a spokesman worried consumers will balk at the added price. Much of the technology already is available, the alliance noted, but consumers haven't bought it.
The proposed regulations are "performance based," Lloyd said, leaving it to manufacturers to determine how to comply rather than dictating specific measures they must take. The air board staff concluded there would be no significant impact on the state's economy or on consumers' buying habits.
The draft recommendations will be open to public comment through July 7, with final recommendations out in August for a board decision in September.
Automakers can trim greenhouse gas emissions by improving the performance of car engines, transmissions and drive trains using existing or pending technology, the board's staff concluded after hearing from experts in automotive design, emissions control systems, and global climate change over the last several months.
California is the only state that has been able to set its own vehicle pollution standards, because California began regulating pollution before the federal government did.
Other states can adopt either federal vehicle pollution standards or California's. Several states in the Northeast, including New York, generally use California's standards, which could bring even more pressure on automakers to build more fuel-efficient vehicles.
California already has the nation's most stringent standards for other vehicle pollutants.
The Natural Resources Defense Council called on automakers to adopt the new technology instead of fighting pending regulations it said could have a ripple effect across the country.
Gov. Arnold Schwarzenegger has expressed support for the law, and promised to fight any challenges by automakers or the federal government.