Massachusetts v. EPA (2007)
Massachusetts v. EPA (2007) is a landmark Supreme Court decision holding that greenhouse gases are "air pollutants" under the Clean Air Act and that the EPA must regulate them if they endanger public health or welfare[1][2][3][4][5][6][8]. The case established state standing for climate litigation and triggered the first federal regulatory actions on CO₂, fundamentally shaping U.S. climate policy through 2025[7][8][15][16].
Key Events Timeline
- 1999: 19 organizations petition EPA to regulate GHGs from new vehicles under the Clean Air Act[2][4][8].
- 2003: EPA denies petition, claiming lack of authority and policy grounds[1][4][5].
- 2005: D.C. Circuit upholds EPA’s denial; Massachusetts and 11 states appeal[1][4][5].
- Nov 29, 2006: Supreme Court hears oral arguments on standing and EPA’s obligations[1][3][4].
- April 2, 2007: Supreme Court (5-4, Stevens, J.) holds states have standing, GHGs are pollutants, and EPA must regulate if endangerment is found[1][2][3][4][5][6][8].
- 2009: EPA issues "Endangerment Finding," concluding GHGs threaten public health and welfare[8].
- 2011-2015: EPA implements GHG standards for vehicles and power plants (Clean Power Plan)[8].
- 2022-2024: Supreme Court narrows EPA authority (West Virginia v. EPA), but Massachusetts v. EPA remains controlling law[8].
Supreme Court Vote
U.S. Greenhouse Gas Emissions and EPA Regulatory Milestones
| Year | Total GHG (MtCO₂e) | EPA GHG Policy Action |
|---|---|---|
| 2005 | 6,650 | Pre-Massachusetts v. EPA |
| 2007 | 6,500 | Supreme Court decision |
| 2009 | 6,400 | Endangerment Finding |
| 2012 | 6,150 | Vehicle GHG standards begin |
| 2015 | 5,900 | Clean Power Plan |
| 2020 | 5,200 | COVID-19 emissions dip |
| 2024 (proj.) | 5,400 | Post-Chevron, regulatory uncertainty |
Result: U.S. GHG emissions declined ~19% from 2005-2024, with most reductions after EPA began regulating under Massachusetts v. EPA. Policy uncertainty increased after the Chevron doctrine was overruled in 2024[8][12][14][15][16].
Who Had Standing? States and Organizations
| Plaintiff States | Key NGOs | Defendants |
|---|---|---|
| Massachusetts, California, Connecticut, Illinois, Maine, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont, Washington | NRDC, Sierra Club, Environmental Defense, Greenpeace, Union of Concerned Scientists | EPA, U.S. Federal Government |
Legal Logic and Precedent
Key Holdings
- Standing: States have standing to sue EPA due to "special solicitude" for sovereign interests and measurable harm from sea level rise[1][3][4][5][6].
- Statutory Interpretation: Greenhouse gases are "air pollutants" under the Clean Air Act’s broad definition[1][2][4][5][6].
- Agency Duty: EPA cannot decline to regulate GHGs for policy reasons alone; it must make a science-based endangerment finding[1][2][4][5][6].
Implications for Climate & Administrative Law
| Area | Before Massachusetts v. EPA | After Massachusetts v. EPA |
|---|---|---|
| EPA Authority | No federal GHG regulation; EPA claimed no authority | EPA must regulate GHGs if science shows endangerment |
| Climate Litigation | States and NGOs lacked standing for climate suits | States/NGOs can sue EPA for climate inaction |
| U.S. Climate Policy | Fragmented, state-led, no federal standards | Federal vehicle and power plant GHG standards, Clean Power Plan, regulatory rollback risk after 2024 |
| Legal Precedent | Clean Air Act not seen as a climate law | Clean Air Act is a climate law; GHGs are pollutants |
Why Massachusetts v. EPA Matters
Massachusetts v. EPA is the legal foundation for all federal climate regulation in the U.S. It established that states have standing to challenge climate inaction, that greenhouse gases are air pollutants, and that EPA must regulate them based on science[1][2][3][4][5][6][8]. The decision enabled vehicle and power plant GHG standards and remains controlling law, even as the Supreme Court has narrowed EPA’s powers since 2022.
Key citation: Massachusetts v. EPA, 549 U.S. 497 (2007); Clean Air Act §202(a)(1).