A week after the U.S. Supreme Court said vehicle carbon dioxide emissions can be regulated like other pollutants, an effort by several states to do that is about to get its first court test.
California long has been the pacesetter in regulating car emissions, setting tougher limits than those imposed by the federal government.
To avoid having cars built to meet 50 different sets of state rules, federal law allows other states to choose between the federal and the California rules. Vermont, New York and eight other states follow California.
But on Tuesday, the focus shifts to Vermont, where a trial begins over new rules -- adopted by California in 2005 and soon after by the other states -- designed to reduce emissions of the greenhouse gas carbon dioxide.
The trial is the first of a series of court fights expected in the states.
"Vermont is the first court in the nation to decide this issue and that will potentially have enormous impact," said Melissa Hoffer, vice president of the Conservation Law Foundation, one of several environmental groups involved in the case.
Charles Territo, spokesman for the Alliance of Automobile Manufacturers, called the case "very important, because it's the first trial where the issue of whether or not states have the authority to set their own fuel economy standards will be decided."
At issue is which set of federal regulations will control vehicle carbon emissions.
The auto industry argues that the only way to reduce carbon emissions is to improve vehicle mileage, because carbon emissions depend on how much fuel is burned. The U.S. Department of Transportation sets fuel economy standards; federal law -- the Energy Policy and Conservation Act -- pre-empts states from doing so.
The EPA made the same argument in determining that it would not set limits for carbon emissions, but the Supreme Court rejected the assertion.
Territo said the states' rules would ratchet down carbon emissions until fleet average fuel efficiency would be 43 miles per gallon by 2016.
Much of the trial is expected to feature experts testifying about whether that goal is technically achievable -- and economically wise.
The automakers say the state rules fail on both counts. Environmental groups counter that the goals are achievable with current technology.
The states and the environmental groups in their corner don't think carbon emissions should be ruled by the Department of Transportation fuel economy standards. Instead, they want the Clean Air Act to hold sway.
That 1970s law allowed California to set more stringent emissions rules than the federal government, in recognition of that state's smog problems and that it passed regulations before the federal government did.
It also allowed other states to piggyback on the California rules, effectively setting up a system in which there are "federal cars," built for less stringent emission limits and "California cars" built for tighter ones.
Amid growing concern about global climate change, California decided in 2005 to add carbon to the list of pollutants it would regulate under the Clean Air Act, effective with the 2009 model year.
Vermont and eight other states -- Connecticut, Maine, Massachusetts, New Jersey, New York, Oregon, Rhode Island and Washington -- followed suit, and Maryland is expected to join when Gov. Martin O'Malley signs a bill passed by its Legislature last week.
Hoffer says the federal fuel economy law doesn't trump the Clean Air Act. There is an "unbroken precedent" of the Department of Transportation taking Clean Air Act emissions limits into account when it sets fuel economy standards, she said.
In its ruling last week, the U.S. Supreme Court appeared to agree that the EPA and DOT can work in tandem.
The majority said "that DOT sets mileage standards in no way licenses EPA to shirk its environmental responsibilities. EPA has been charged with protecting the public's health and welfare, a statutory obligation wholly independent of DOT's mandate to promote energy efficiency. The two obligations may overlap, but there is no reason to think the two agencies cannot both administer their obligations and yet avoid inconsistency."