Wednesday, 20 September 2006, 22:40 GMT 23:40 UK
About one-third of California's CO2 emissions come from trafficThe state of California is suing six carmakers for costs associated with their cars' greenhouse gas emissions.
The suit names General Motors, Toyota, Ford, Honda, Chrysler and Nissan.
California is asking for "monetary compensation" for the damage which it says their emissions are doing to health, economy and environment.
The Alliance of Automobile Manufacturers (AAM), a pan-industry body, called it a "nuisance" suit and suggested it may be dismissed.
"Right now, global warming is harming California," runs the state's complaint.
"Human-induced global warming has, among other things, reduced California's snow pack (a vital source of fresh water), caused an earlier melting of the snow pack, raised sea levels along California's coastline, increased ozone pollution in urban areas, [and] increased the threat of wildfires."
State lawyers want any judgement for damages to be ongoing, so that manufacturers will be liable every year.
Guto Hari, the BBC's North American business correspondent, notes that California has taken an aggressive stance on global warming, passing legislation to significantly reduce carbon dioxide emissions by 2020.
'Time to answer'
The lawsuit, lodged on behalf of the Californian people by state attorney-general Bill Lockyer, alleges that emissions from cars made by the firms in question account for 30% of all carbon dioxide emissions in California.
The complaint alleges that the firms' activities have harmed the state's environmental health, with California having to spend million of dollars responding to environmental threats such as coastal erosion.
Mr Lockyer said he had not put a figure of the level of damages he was seeking but that it was likely to run into "hundreds of millions of dollars".
"Global warming is causing significant harm to California's environment, economy, agriculture and public health," he added.
"The impacts are already costing millions of dollars and the price tag is increasing. It is time to hold these companies responsible for their contribution to this crisis."
This is the latest in a series of legal and quasi-legal cases in the US aimed at forcing reductions in greenhouse gas emissions
- An Inuit group is taking the federal government to the Inter-American Commission for Human Rights
- Conservation groups are trying to force the government to protect coral and polar bears from the effects of global warming
- There are ongoing attempts to force the Environmental Protection Agency to define CO2 as a pollutant and regulate emissions
Roda Verheyen of Climate Justice, an international organisation which co-ordinates legal climate cases, said California's suit took action to a new level.
"It is the most significant piece of climate change litigation that has ever been brought," she said.
Car manufacturers have their own case against California pending over laws requiring them to reduce emissions.
The AAM said in a statement: "Automakers will need time to review this legal complaint [by California], however, a similar nuisance suit that was brought by attorneys-general against utilities was dismissed by a federal court in New York."