EPA Cannot Impose Emission Limits Based Only On Greenhouse Gases

The U.S. Supreme Court's decision Monday, June 23, limits EPA's authority to impose limits on emissions of greenhouse gases ("GHGs").   Reviewing challenges to EPA's rule limiting GHGs under the Clean Air Act's provisions of Prevention of Significant Deterioration ("PSD") and Title V permitting, the Court held that the Act did not require that EPA impose limits on GHGs in instances where the GHGs were the only pollutants to trigger compliance with PSD and Title V requirements. 

The Court also held that EPA's interpretation of its authority under the Act was not a reasonable interpretation and so the agency's interpretation was not eligible for deference under the Chevron line of cases.