Massachusetts v. EPA (2007)

1) Link to the Actual Opinion
Read the U.S. Reports opinion (PDF)

2) Summary of the Opinion
A group of states, led by Massachusetts, sued the EPA for refusing to regulate greenhouse gases from motor vehicles under the Clean Air Act. The Supreme Court held that greenhouse gases are air pollutants under the Act and that the EPA has authority—and responsibility—to regulate them if they endanger public health or welfare.

3) Why It Mattered
This was the Court’s first major climate change ruling, forcing the federal government to treat carbon emissions as pollutants. It empowered environmental regulation and climate policy for decades to come.

4) What It Provided or Took Away

• Provided: Legal authority for the EPA to regulate greenhouse gases.
• Took Away: The EPA’s discretion to ignore climate change when applying the Clean Air Act.

5) Overreach or Proper Role?
The Court applied the statute’s plain text. Critics said it pushed environmental policy into the courts, but it was a faithful reading of congressional intent.

6) Plain-English Impact Today
This case is why carbon dioxide and other greenhouse gases are regulated like other pollutants. It laid the foundation for U.S. climate policy.

• Environment
• Epa
• Clean Air Act
• Climate Change