The Environmental Protection Agency (EPA) did not regulate carbon dioxide (CO₂) emissions from motor vehicles until after the United States Supreme Court ruled that the EPA had the authority to do so because

A) the Clean Air Act does not mention CO₂ emissions.
B) scientists do not all agree that CO₂ contributes to climate change.
C) climate change has widespread effects, not particularized harms.
D) CO₂ emissions constitute a public danger.

The Clean Air Act, which is the primary federal law regulating air pollution in the U.S., did not specifically mention carbon dioxide (CO2) emissions, leading to initial uncertainty over the EPA's authority to regulate them. This was clarified by the Supreme Court's decision in Massachusetts v. EPA (2007), which held that greenhouse gases, including CO2, are air pollutants covered by the Clean Air Act, thus giving the EPA the authority to regulate their emissions from motor vehicles.