A US federal judge has dismissed a case brought by California against six leading carmakers over alleged damage caused by cars' CO2 emissions.
About one-third of California's CO2 emissions come from traffic
The legal action, the first of its kind, demanded millions of dollars in compensation from General Motors, Ford, Honda, Toyota, Chrysler and Nissan.
But the judge ruled that the issue of whether carmarkers were accountable was a political, not legal, matter.
Officials said they were disappointed, adding they may appeal the ruling.
The lawsuit, filed by California's former Attorney-General Bill Lockyer in September 2006, wanted to make the manufacturers liable for the damage he said was caused by greenhouse gas emissions from the state's estimated 32 million registered vehicles.
It said that the producers has created a "public nuisance" by making "millions of vehicles that collectively emit massive quantities of carbon dioxide".
The complaint added that human-induced climate change had resulted in a range of environmental impacts across the state, including reducing the state's snow pack, rising sea levels, and increased ozone pollution in urban areas.
But in his written ruling, District Judge Martin Jenkins wrote that it would be necessary for a decision to be made as to what volume of greenhouse gas emissions would be deemed "unreasonable" before a court could make a ruling.
"The court finds that injecting itself into the global warming thicket at this juncture would require an initial policy determination of the type reserved for the political branches of government," he wrote.
Ted Boutrous, who represented the carmakers, said the six manufacturers welcomed the ruling.
"[Climate change] is very complicated and this court said it is best left to national lawmakers to determine policy," he told AP.
California's supervising deputy attorney general Ken Alex told AFP that state officials were considering their options.
"Obviously, we're very disappointed with the ruling, and we're going to read it very carefully," he said.
"We certainly have the ability to file an appeal... and that will be part of our calculations."
Mr Alex added that the state brought the action on behalf of the people of California because national authorities had failed to act over setting emission targets.
"We do think that because the federal government has failed to act, this is a judicial obligation to jump in where those entities had failed to act."