In its first case confronting global warming, the U.S. Supreme Court ruled in April that greenhouse gases such as carbon dioxide are air pollutants that the Environmental Protection Agency can regulate. As a consequence, experts agree that greenhouse emissions from automobiles and possibly power plants will face regulations. The debate now will focus on how strict—or lax—those rules will be.

The EPA had long claimed to have no authority in regulating these gases because they were not air pollutants under the Clean Air Act. Moreover, the agency also stated that even if it did have the power to regulate such gases, it would not do so. Discontented with the federal response to global warming, environmental groups joined forces with three cities, one U.S. territory and a dozen states, led by Massachusetts, to challenge the EPA in court. Siding with the EPA were several industry groups and 10 states, a number of which rely heavily on coal, electricity or motor vehicle production.

In a 5–4 decision against the EPA, the Supreme Court majority decided that the scientific evidence (some of which came from the agency itself) suggested that Massachusetts and other states were experiencing harm from global warming and that the EPA had the authority to redress it. For instance, rising sea levels “meant hundreds of millions of dollars were at risk in terms of damage to our coastline,” explains James Milkey, assistant attorney general for Massachusetts.

In the face of the Supreme Court decision, the EPA could still refuse to control tailpipe emissions of greenhouse gases, but such action will prove problematic given the decision and the EPA’s mandate to regulate dangerous pollutants under the Clean Air Act. If the agency were to refuse, “there’d be a lawsuit against them that would win,” predicts Michael Herz, an environmental, constitutional and administrative law professor at the Benjamin N. Cardozo School of Law in New York City. Indeed, in May, President George W. Bush ordered federal agencies to work toward regulations to reduce motor vehicle greenhouse gas emissions and gasoline consumption.

Mass. v. EPA, as the case is known, should affect a number of other decisions around the nation that had been placed on hold. Notably, California and 11 other states had been seeking waivers from the EPA permitting them to pass laws requiring reduced car emissions of greenhouse gases from the 2009 model year onward. Cars release these gases as they burn fuel, so the proposed reduction in emissions “effectively means higher fuel mileage cars,” Herz points out. (Federal laws prevent states from setting their own mileage standards.) California governor Arnold Schwarzenegger has threatened that his state would sue the EPA if the agency did not decide on the waiver by the end of October.
The major result of Mass. v. EPA “is that business will go and try to make a deal with Congress regarding federal regulations on greenhouse gas emissions,” says Mary Nichols, director of the Institute of the Environment at the University of California, Los Angeles, and former EPA assistant administrator of air and radiation. “Congress is not just going to let the EPA take control of this issue.”

In essence, such federal laws could resemble “homegrown versions of the Kyoto Protocol,” Herz says, referring to the international agreement to reduce greenhouse gas emissions. “At this point, it’s going to be a battle about stringency and not whether or not standards will happen.”

In the absence of federal legislation, some states have already seized the initiative and could set the tone for the rest of the nation. Ten northeastern and mid-Atlantic states are participating in the first mandatory program in the U.S. devoted to fighting global warming. Called the Regional Greenhouse Gas Initiative, the group seeks to cut current emissions by 10 percent by 2019 through a cap-and-trade system. Such a system limits the total amount of greenhouse gases emitted while allowing companies to pay for releasing more or to earn credit for spewing less.

Still, any federal regulations that Congess helps to create would probably preempt state laws regarding greenhouse gas emissions from tailpipes and elsewhere, Nichols points out. They would tell “California and the others they can’t do anything they want to,” she says. The Alliance of Automobile Manufacturers, which supported the EPA in the Supreme Court case, “certainly believes there needs to be a comprehensive federal policy in place to reduce carbon dioxide, and we intend to work constructively with members of Congress on that issue,” says alliance spokesperson Charles Territo. The Supreme Court ruling may represent a milestone in the legal battle over climate change, but a long, hard road most likely remains ahead.