California Governor Gray Davis signed a law on Monday regulating vehicle gas emissions to help curb global warming. It is the first state law requiring auto makers to limit carbon dioxide emissions and other pollutants that scientists have said blanket the atmosphere and lead to warmer temperatures and other harmful effects on humans and other living creatures.

The legislation would not take effect until 2006, but gives auto companies until 2009 to make technological changes that conform to the new California standards.

U.S. automakers intend to legally challenge California's new emissions law, arguing that it is superceded by federal legislation already in place.

"We've already said we intend to pursue legal action, because this is pre-empted federally by the energy policy and conservation act, which sets fuel economy standards," said Greg Dana, vice president of environmental affairs for the Alliance of Automobile Manufacturers in Washington.

"We don't think they can do it. We intend to challenge it because it is a federally pre-empted issue," Dana added.

Experts said federal law grants authority to the federal government to set fuel standards above individual states.

"This has come up many times over the past 10 years, and the federal pre-emption has always stopped the states," said Klimisch.

The National Highway Traffic Safety Administration, which is part of the Department of Transportation, is currently preparing new carbon-dioxide emission standards for the 2005 model year for light trucks, which are the same emissions outlined in Calfornia's law, industry experts said.

The deadline for NHTSA regulations is April 2003, and will come well before the California law is due to take effect.

"In spite of what you're hearing in the press about this (California law) being about emissions, it's not really emissions in the traditional sense. It's really to control CO2 emissions, which is nothing more than fuel economy. For that reason, aluminum is something people consider," said Dana.

By trimming an automobile's weight, the amount of fuel needed to run the car, and in turn emissions, are lessened.

Light-weight aluminum has been used by car companies, along with light-weight steel, plastics and other materials to reduce the overall weight of a vehicle to comply with tighter fuel standards already in place.

And, car manufacturers are continuing to explore new ways to safely design vehicles that are lower in weight.

While the big auto companies do not yet know exactly how stringent the NHTSA standards will be next year, they are already anticipating lighter truck designs, more efficient engines, and other technology to reduce emissions.

"We're doing everything we can to try to help the automakers reach higher fuel economy standards. That's one of the things aluminum can do, without compromising safety," said Klimisch.

Dana said there is no gadget you can put on a car to lower carbon-dioxide emissions, which instead must be achieved by improved engine technology, lower weight or other technological advances to a car's systems.

"There is no filter or catalyst you can put on a car to reduce CO2 emissions. Catalysts are very good at reducing hydro-carbons and carbon-monoxide emissions, but not carbon-dioxide," said Dana.

"Our concern is that NHTSA will set standards that would go far beyond what the technology alone can do," said Dana.

According to Klimisch, NHTSA's record in both safety and fuel economy has rendered them one of the most highly respected agencies in the government.