The Clean Air Act was enacted in 1970, at the birth of the environmental movement, and is the primary law defining the E.P.A.’s responsibilities for protecting and regulating air quality. It was significantly expanded in 1990 to curb other major environmental threats like acid rain and urban smog.
The act does define greenhouse gases in some sections, but does not explicitly direct the Environmental Protection Agency to regulate carbon dioxide. Rather, it more broadly asks the agency to regulate pollutants that “endanger human health.” In 2007, the Supreme Court, in Massachusetts vs. E.P.A., No. 05-1120, ordered the agency to determine whether carbon dioxide fit that description. In 2009, the E.P.A. concluded that it did.
That conclusion meant carbon dioxide could be legally defined as a pollutant and regulated. The Obama and Biden administrations used that finding to justify regulations on gasoline-powered vehicles and coal and gas-burning power plants, and several Supreme Court cases subsequently upheld that authority.
Yet, because Congress had never before directly addressed the issue, challenges have continued. In West Virginia vs. E.P.A., No. 20-1530, the landmark ruling this year, conservative Supreme Court justices made clear that if lawmakers really wanted the government to move away from fossil fuels, they should say so.
“One threshold assumption in the ruling was that Congress had not made it abundantly clear that E.P.A. had a responsibility to address climate pollution from the power sector,” said Vickie Patton, general counsel for the Environmental Defense Fund. “Well, it is now abundantly clear,” she said.
Some experts played down the effect of the provisions. Jeff Holmstead, an energy lawyer who served in the E.P.A. during both Bush administrations, said there was a near-zero chance that legal efforts by some conservative groups to eliminate the government’s ability to regulate climate pollution would have prevailed anyway.
