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In February, the U.S. Environmental Protection Agency rescinded a 2009 finding that greenhouse gas emissions (GHG) were a threat to public health. The 2009 finding followed the Supreme Court’s 2007 ruling in Massachusetts v. EPA, which held that greenhouse gas emissions constitute air pollution subject to regulation by the EPA under the Clean Air Act.

The endangerment finding provides the legal foundation for regulations aimed at protecting against the increasing threats from climate change, such as increased floods, wildfires, and extreme heat.

The last three years have been the hottest on record and 2025 marked the first time that the three-year-temperature average breached the threshold set by the Paris Agreement to limit warming to no more than 1.5 degrees Celsius above pre-industrial levels.

YSE News spoke with Daniel Esty, the Hillhouse Professor of Environmental Law and Policy, and Jennifer Marlon, senior research scientist, about the impacts of the EPA decision.

Q. How will this decision affect the Clean Air Act?

Esty: If upheld after legal challenges, EPA Administrator Lee Zeldin’s decision to rescind the 2009 endangerment finding takes away the legal basis for regulating GHG emissions. But it would not affect the legal foundation for regulation under the Clean Air Act of the six air pollutants named in the statute: ground-level ozone that causes smog, particulate matter, carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead. Note that continued regulation of these pollutants will lead to policies that in many cases (as a secondary effect) limit GHG emissions.

Three-quarters of Americans want the government to regulate carbon dioxide as a pollutant. This repeal moves us in the exact opposite direction from what the public wants. That gap between policy and public will is not sustainable.”

Q. What are some of the potential short and long-term impacts of the decision on environmental policy.

Esty: In the very short term, the decision brings a halt to federal regulation of GHG emissions from vehicles and potentially power plants. The intermediate-term impact depends on the legal logic of the future judicial decisions in the court cases that will follow. Of particular note is the fact that the EPA rejects both the climate change science of the original finding and its legal foundations. If the Supreme Court accepts the administration’s view of the science, the EPA would no longer be in a position to directly regulate GHG emissions from power plants or vehicles.

If, however, the Supreme Court goes further and accepts the administration’s argument that (1) GHGs do not fit under the Clean Air Act definition of air pollutant or (2) that whether to address GHGs represents a significant expansion of regulatory authority, then climate change regulations in the U.S. would not be able to go forward until the Congress adopts legislation providing a GHG regulatory regime.

Q. What are some of the ways the EPA decision could affect the lives of Americans?

Marlon: It will make it harder for Americans to know how polluted their air and water is, to know who is doing the polluting, and to hold polluters accountable. Farmers will likely face more volatile growing seasons with no federal support to adapt; parents could see their children’s asthma worsen as heat waves and smoke days increase; and an increasing number of homeowners may lose insurance or won’t be able to get insurance because their zip codes are now considered to be in areas where there is a flood or wildfire risk.

Esty: The President’s energy dominance agenda with its priority focus on fossil fuels has already led major automakers to pull back from their investments in electric vehicles and imposed new obstacles for wind power producers and other clean energy companies. The administration has said that these moves will translate into cheaper cars and lower electricity costs, but so far, no such consumer benefits have emerged. And we must be clear that lowering the price of cars by allowing pollution to go unabated is not free; it simply imposes hidden costs on those who suffer the consequences of the resulting air pollution or climate change impacts that emerge over time. A further consequence will be diminished U.S. competitiveness in critical industries of the future, including electric vehicles, solar arrays, wind turbines, and batteries. Across the world, we see Chinese products in all these categories surging into new markets.

Q. In what other ways can climate change be addressed?

Esty: The work toward a sustainable future goes on. Even in the United States, growth in clean energy over the past year was substantial with over 90% of the new electricity generation brought online in 2025 coming from renewable power sources and batteries. The pace of solar and wind power expansion will likely slow in the coming year, but many private sector actors see renewable energy as the foundation of the 21st century economy.

Many companies now recognize that they will need to transition their business models in a more strategically careful way so that they can meet their GHG emissions reduction pledges while maintaining their competitive posture and honoring the affordability concerns of their customers.

Moreover, as the federal administration pulls back from a leadership posture on climate change, governors and mayors across the country are stepping up their commitments, as are other nations.

Marlon: Work is continuing on all fronts because millions of Americans understand what is at stake and majorities of Americans believe we should be protecting resources for future generations. Three-quarters of Americans want the government to regulate carbon dioxide as a pollutant. This repeal moves us in the exact opposite direction from what the public wants. That gap between policy and public will is not sustainable, and the people, cities, states, businesses, and researchers who have been doing this work aren’t stopping. The political winds shift; the science doesn’t.

Read more from Todd Cort, lecturer in sustainability, on the decision’s impact on markets.