All eyes on Vermont.

The U.S. Supreme Court ruled in April that vehicle carbon dioxide (C[O.sub.2]) emissions can be regulated like other pollutants. Now, federal courts will decide if the 10 states that adopted California's stricter limits on emission of C[O.sub.2] have a right to do so. Vermont is first in line.

To avoid the chaos of having cars built to meet 50 different sets of state rules, federal law requires states to choose between the federal or California rules. In 2005, California added carbon to the list of pollutants it would regulate under the Clean Air Act. The federal Clean Air Act set national air quality standards but allowed California to write its own, stricter standards with EPA approval, which is yet to come.

Automakers are asking U.S. District Judge William Sessions to throw out Vermont's adoption of California's carbon dioxide emissions limits on grounds that they are illegal, too expensive to engineer and are certain to deny many drivers the chance to buy a SUV or pickup truck of their choice. Vermont and its allies--New York and five environmental groups--defend the rules as a legal, reasonable, affordable and necessary step to combat global warming.

Even if Judge Sessions upholds the legality of Vermont's regulation, implementation could be many years away, if it happens at all. The losing side is expected to appeal. Meanwhile, similar cases are pending in California and Rhode Island.

Where a decision in the Vermont case would apply only there, the ruling in the California case, if it goes to trial, would affect every state.