With the stroke of a pen the governor of California took action that could end up drastically changing automobiles in the future.

Gov. Gray Davis signed legislation Monday requiring stricter emission standards for all new cars sold in the state beginning in 2009, a move that Davis said will help cut down on the 40 percent of carbon dioxide emissions produced by California cars and light trucks.

"If we don't begin to reduce greenhouse gases, the climate will be disruptive, the air will be fouled, and our economy will be weakened," Davis said in a bill signing along a park trail.

Though the legislation doesn't affect the big polluting vehicles like tractor-trailers and other commercial trucks, the move is likely to have a huge impact on the car of the future. California, which has the fifth largest economy in the world, is the nation's most populous state, and its residents buy 10 percent of the nation's automobiles.

California has already passed laws requiring automakers to meet stricter pollution standards for vehicles sold there. As a result, heavy smog days there are largely a problem of the past.

Many of the pollution-cutting innovations first tried in California are now used in cars driven in the other 49 states. But carmakers say cutting greenhouse gas emissions is a more difficult task.

The D.C.-based organization that represents car manufacturers is predicting that California residents will wake up one day and see their beloved SUVs and trucks gone.

"With this legislation in place, it is very likely that some of those vehicles would become unavailable to California consumers. So the California consumers are not going to have the same vehicle choices that people in the rest of the country have," said Josephine Cooper, CEO of the Alliance for Automobile Manufacturers.

But the clean air activists who helped to write the California legislation say they have heard these complaints from carmakers before.

"The automakers have been crying wolf for many years now. Seatbelts, airbags, catalytic converters, I mean every single time there's been a major single advance in the technology they scream and yell. They testify before Congress that we're gonna go bankrupt if you do this to us. It couldn't be more false," said Russell Long, executive director of the Bluewater Group, a national environmental organization based in San Francisco.

Automakers have threatened to sue to have the legislation overturned or to try to force the issue as a ballot initiative this fall, but activists are betting that carmakers won't pass up 10 percent of the marketplace, and will eventually decide it's easier to make one car that meets California standards than one car for California and another car for all the other consumers.