EPA Endangerment Finding Reversed: Science, Law, and Climate Regulation

Science Friday examines the Trump administration’s rescission of the 2009 endangerment finding, a cornerstone for regulating greenhouse gases under the Clean Air Act. Host Flora Lichtman talks with Dr. Andy Miller, an original author on the finding, about why this legal mechanism matters, how it shaped vehicle-emission standards, and what it could mean for future regulation. The discussion traces the Massachusetts versus EPA case that catalyzed the finding, recalls the internal EPA process from 2007 to 2009, and weighs the role of science in climate policy as regulatory battles unfold. The episode offers context on how regulatory actions intersect with science and markets, and what comes next for emissions and policy.

Introduction and topic framing

Flora Lichtman introduces a major shift in federal climate policy: the rescission of the 2009 endangerment finding, a legal basis under the Clean Air Act for regulating greenhouse gases. The finding defined greenhouse gases as air pollutants and obligated the EPA to regulate them. The host emphasizes the political and legal stakes, and the need to understand what this means for regulation, industry, and public health.

“It's huge. It officially and legally defines greenhouse gasses as air pollutants.” - Flora Lichtman

Massachusetts versus EPA and the turning point

The episode revisits the Massachusetts versus EPA decision, a 2007 Supreme Court ruling that greenhouse gases fit the Clean Air Act’s definition of air pollutants and thus required EPA action. Flora explains how this decision set the stage for the endangerment finding and subsequent rules, including vehicle-emission standards. Dr. Andy Miller, an author on the finding who served at the EPA for more than 30 years, explains the legal and scientific sequence that led to the rule and why its removal matters for regulatory authority.

“It’s a big deal from an EPA perspective.” - Dr. Andy Miller, EPA

The endangerment finding and its effects on regulation

The conversation outlines what the endangerment finding accomplished. It provided a formal basis to regulate greenhouse gas emissions from vehicles under the Clean Air Act, with substantial impact on automotive standards, while also codifying reductions in power-plant emissions amid energy shifts from coal to natural gas and renewables. The discussion weighs how consumer behavior, technology adoption, and overseas competition continue to drive efficiency even if regulatory leverage wanes.

“The immediate impact was that it allowed EPA to regulate greenhouse gasses from vehicles.” - Flora Lichtman

Behind the scenes: internal EPA process and political context

Miller recounts the internal EPA work in the Bush and Obama administrations, including the Office of Management and Budget’s (OMB) reception of the finding. An anecdote about an unopened OMB email late in the Bush era illustrates how political processes influenced scientific actions. Lichtman connects this history to the formation of the 2009 rule, highlighting how scientific assessments navigate legal and administrative pathways before becoming regulatory standards.

Outlook: science, regulation, and the path forward

Both participants reflect on the resilience of climate science and the broader regulatory landscape. Miller argues that while the finding may be rescinded, the scientific consensus on climate change remains solid, and external pressures—international competition, technological innovation, and evolving public demand—will continue to push emissions reductions. Lichtman cautions that legal challenges from states are likely to persist, but the science itself is not overturned. The episode closes with a sense that regulation will continue to evolve, and the scientific understanding will still underpin future policy decisions.

"The science wins" - Dr. Andy Miller, EPA