The Legal Foundation of US Climate Policy Under Threat

Buried beneath the daily torrent of political news is a regulatory battle that could have more lasting environmental consequences than almost any other action taken by the current administration. The Trump White House is moving to dismantle the Environmental Protection Agency's endangerment finding, a 2009 scientific and legal determination that forms the bedrock of virtually all federal climate regulation in the United States.

For most people, the endangerment finding is an obscure piece of bureaucratic machinery. But for environmental lawyers, climate scientists, and the fossil fuel industry alike, it is the single most important regulatory document in American environmental policy. Understanding what it is and why its elimination matters requires a brief journey into the intersection of science, law, and politics.

What Is the Endangerment Finding?

In 2007, the Supreme Court ruled in Massachusetts v. EPA that greenhouse gases qualify as air pollutants under the Clean Air Act and that the EPA was obligated to determine whether they endanger public health and welfare. After an exhaustive review of the scientific literature, the EPA issued its endangerment finding in December 2009, concluding that six greenhouse gases, including carbon dioxide and methane, do indeed pose a threat to human health and the environment.

This finding did not itself impose any regulations. Instead, it established the legal predicate for the EPA to regulate greenhouse gas emissions under the Clean Air Act. Every major climate regulation issued by the federal government since 2009, from vehicle fuel efficiency standards to power plant emission limits, traces its legal authority back to this determination.

  • The finding covers six greenhouse gases: carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride
  • It was based on a comprehensive review of peer-reviewed scientific literature
  • The Supreme Court upheld the EPA's authority to make such a determination
  • It serves as the legal foundation for all federal greenhouse gas regulations