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endangerment finding
Any Trump EPA Attempt to Stop Regulating Climate Pollution Won’t Stand up to the Facts
The science on climate change is so indisputably well-established, that it’s hard to see how any court would uphold a challenge to it.
Apr 13, 2025
In a blitz of destructive actions announced by Environmental Protection Agency Administrator Lee Zeldin last month, he specifically called for a reconsideration of the 2009 Endangerment Finding. A formal proposal for reconsideration of the finding (and all the agency regulations and actions that depend on it) is expected this month.
The science underpinning the Endangerment Finding is airtight, but that won’t stop the Trump administration from setting up a rigged process to try to undo it and give a blank check to polluters. The Union of Concerned Scientists (UCS) will fight back to defend climate science and protect public health safeguards.
In an earlier post, I laid out some of the history and context for the 2009 science-backed Endangerment Finding and the Cause or Contribute Finding. These findings followed from the landmark 2007 Mass v. EPA Supreme Court ruling which held that greenhouse gas (GHG) emissions are unambiguously air pollutants covered by the Clean Air Act. Together, these establish the clear basis for EPA’s authority and responsibility to set pollutions limits for heat-trapping emissions from vehicles, power plants, and other sources of these pollutants, under the Clean Air Act.
There is nothing mysterious about the heat-trapping attributes of greenhouse gases, nor their impact on public health. It’s called science.
Attacks on the Endangerment Finding and EPA’s Clean Air Act authority from industry interests are nothing new. Importantly, courts have repeatedly upheld both, including in a resounding 2012 decision from the U.S. Court of Appeals–D.C. Circuit in Citizens for Responsible Regulation v. EPA. But those who have long sought to overturn or weaken regulations to limit heat-trapping emissions now have Administrator Zeldin in their corner. And he has shown himself to be an unbridled purveyor of disinformation and proponent of harmful attacks on bedrock public health protections, as my colleague Julie McNamara highlights.
The details of what will be included in the reconsideration proposal are unclear at this point. But we do know some of the trumped-up lines of attack the Zeldin EPA could advance to try to invalidate these findings because many of these tired arguments are outlined in EPA’s reconsideration announcement.
Here are the facts:
Fact No. 1: The Science Backing the Endangerment Finding Is Beyond Dispute
Every major scientific society endorses the scientific consensus on human-caused climate change driven by GHG emissions. The Fifth National Climate Assessment (NCA5) and the IPCC’s Sixth Assessment Report are two major recent authoritative summaries of peer-reviewed climate science, which show that the science on climate change has only become more dire and compelling since 2009.
The impacts of climate change on human health are also starkly clear and backed by overwhelming evidence. Here’s the main finding from the NCA5 chapter on public health, for instance:
Climate change is harming physical, mental, spiritual, and community health through the increasing frequency and intensity of extreme events, higher incidences of infectious and vector-borne diseases, and declines in food and water security. These impacts worsen social inequities. Emissions reductions, effective adaptation measures, and climate-resilient health systems can protect human health and improve health equity.
As just one example, climate change is contributing to worsening extreme heat, which exerts a punishing toll on people’s health, including that of outdoor workers. Heat is already the leading cause of extreme weather-related deaths in the United States, and studies show that heat-related mortality is on the rise.
Looking around the nation, with communities reeling from extreme heatwaves, intensified hurricanes, catastrophic wildfires, and record flooding, climate impacts are the lived reality of all too many people. To deny that or obfuscate about the underlying causes is not only disingenuous, but actively harmful and outright cruel.
Fact No. 2: The Law Requires an Independent Scientific Determination of Endangerment, Unhindered by Cost Considerations
A Finding of Endangerment under the Clean Air Act is specifically focused on a threshold scientific determination of whether the pollutant under consideration harms public health or welfare. Costs to industry of meeting any subsequent regulations are not relevant per the statute.
The original Endangerment Finding was reached in the context of the vehicle emissions, per section 202(a) of the Clean Air Act, partially excerpted below:
The administrator shall by regulation prescribe (and from time to time revise) in accordance with the provisions of this section, standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.
In its 2012 decision, the D.C. Circuit was also clear is noting that “By employing the verb ‘shall,’ Congress vested a non-discretionary duty in EPA.” That duty is not circumscribed by cost considerations.
Of course, the impacts of climate change are themselves incredibly costly and those costs are mounting as heat-trapping emissions rise. Unsurprisingly, the social cost of greenhouse gases, a science-based estimate of those costs, is another metric that the Trump EPA is seeking to undermine in yet another blatant attempt to put a thumb on the scale in favor of polluting industries.
Fact No. 3: EPA Used Well-Established Methodologies in Its Assessment of Six GHGs
As noted in the 2009 Endangerment Finding, the EPA defined the pollutant contributing to climate change as “the aggregate group of the well-mixed greenhouse gases” with similar attributes. The attributes include that they are sufficiently long-lived, directly emitted, contribute to climate warming, and are a focus of science and policy.
The EPA used a very well-established scientific methodology to combine emissions of GHGs on the basis of their heat-trapping potential, measured in carbon-dioxide equivalents. In the case of passenger cars, light- and heavy-duty trucks, buses, and motorcycles—the transportation sources EPA considered for the original Endangerment Finding—they emitted four key greenhouse gases: carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons.
False, glib claims in the reconsideration announcement baselessly accuse the 2009 Endangerment Finding of making “creative leaps” and “mysterious” choices. There is nothing mysterious about the heat-trapping attributes of greenhouse gases, nor their impact on public health. It’s called science. Once again, relying on the mountain of evidence in the peer-reviewed scientific literature would make that readily apparent.
Fact No. 4: EPA Has the Responsibility and Authority to Regulate Major Sources of GHGs
The Cause or Contribute Finding—which specifically established that greenhouse gas emissions from new vehicles contribute to the pollution that harms public health—may also come under attack. This finding has been extended to other major sources of GHGs, including power plants and oil and gas operations. However, the Trump administration could attempt to use accounting tricks to avoid regulating emissions—as it has tried before.
In its first term, the administration attempted multiple underhanded maneuvers along these lines, including in the context of methane and volatile organic compound regulations in the oil and gas sector. For these regulations, the administration split up segments of the source category, designated them as separate source categories, used that manipulation to claim inability to regulate certain segments, and asserted that methane emissions from the remaining segments were too small and regulating them would not provide additional benefits, so those too could not be regulated. Separately, in the final days of the administration, EPA released an absurd framework attempting to set thresholds for determining “significance,” trialed in the context of power plants.
This irrational approach could be used to artificially segment components of power plants or the power system, for example, and then claim no regulations are required. This kind of rigged math wouldn’t fool a kindergarten child, but there’s no telling where this administration might go in its desperate attempt to undo or weaken regulations on greenhouse gas emissions.
Zeldin’s Relentless Subversion of EPA’s Mission
Under Administrator Zeldin, EPA’s mission to protect public health and the environment has been completely subverted. His shocking rhetoric lays bare how far he will go to protect polluters at the expense of the public. Here he is, for instance, crowing about going after 31+ EPA regulations and guidance, as well as the enforcement of pollution standards meant to protect all of us:
Today is the greatest day of deregulation our nation has seen. We are driving a dagger straight into the heart of the climate change religion…
EPA even set up an email address for polluters to send an email to get a presidential exemption from complying with regulations on toxic pollution, such as mercury emissions, regulated under the Clean Air Act!
Zeldin is fervently committed to dismantling public health protections and rolling back enforcement of existing laws passed by Congress. Going after the Endangerment Finding is an integral part of this all-out assault because, in the Trump administration’s harmful calculation, revoking the finding is a potential means to rolling back all the regulations that depend on it.
Ironically, some utilities and oil and gas companies have spoken out in favor of keeping the finding intact, as they fear a greater risk of climate damages lawsuits in the absence of EPA authority to regulate greenhouse gases. Of course, this just exposes that they know their products are causing damage. What they seek is the weakest possible exercise of EPA authority so they can continue to reap profits while evading accountability for those harms.
We Can Fight Back With Science
But none of this is a foregone conclusion. The legal and scientific basis for the Endangerment Finding is incredibly strong. The false claims Zeldin and other opponents have trotted out are full of bombast but weak on substance.
The science on climate change is so indisputably well-established, that it’s hard to see how any court would uphold a challenge to it. That’s not to say Zeldin won’t try to find a cabal of fringe “scientists” to try to attack it, but they’re unlikely to succeed on the merits.
Public comments on the proposal to reconsider the Endangerment Finding can help set the record straight on facts. And if the Zeldin EPA ignores them and finalizes a sham finding or revokes the finding with a faulty rationale, that will be challenged in court.
UCS will be closely following the details of EPA’s proposal to reconsider the Endangerment Finding when it is released. And we will let you know how you can add your voice to bolster this crucial science-based finding, and the public health protections that flow from it. So, stay tuned!
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Ignoring 'Science and the Law,' Trump EPA Readies Chainsaw for Key Climate Finding
"Lee Zeldin is willing to go so far as to break established law to pay back the corporate executives and polluters who spent millions to get Donald Trump elected," said one climate leader.
Feb 26, 2025
Climate advocates said Wednesday that the Trump administration will be abdicating its "clear legal duty to curb climate-changing pollution" if it moves forward with repealing the 16-year-old scientific finding that has underpinned the federal government's actions to protect people and the planet from fossil fuel emissions.
As The Washington Postreported, Environmental Protection Agency (EPA) Administrator Lee Zeldin is pushing the White House to repeal the endangerment finding, an official determination announced in 2009 that affirmed what the fossil fuel industry had known for decades: that emissions of greenhouse gases including carbon dioxide and methane cause planetary heating and threaten public health.
The finding gave the government the authority to regulate such pollution.
For several days, the White House and EPA refused to release the results of a 30-day review of the endangerment finding, which President Donald Trump called for under an executive order he issued on his first day in office.
Three people with knowledge of the issue, who remained anonymous, told the Post that former EPA Chief of Staff Mandy Gunasekara—who wrote the chapter on the agency in the right-wing policy agenda Project 2025—has been advising the administration on the potential repeal of the endangerment finding.
Another former official from Trump's first term, attorney Jonathan Brightbill, is also providing legal advice on repealing the scientific finding, which has provided the basis for federal regulations on automobile, aircraft, and power plant emissions.
By repealing the endangerment finding in place, the administration would throw out thousands of scientific studies showing how fossil fuel emissions heat the planet and are linked to heart disease, lung cancer, asthma, and other life-threatening health problems—and clear the way to overturn climate policies introduced by former President Joe Biden.
Denying the science underpinning the finding, said Green New Deal co-sponsor Sen. Ed Markey (D-Mass.), makes the administration "a danger to our country."
Rachel Cleetus, policy director with the Union of Concerned Scientists' Climate and Energy Program, said that any attempt by the Trump administration to gut the endangerment finding would be "fully challenged in court."
"Eliminating the endangerment finding would be a giveaway to the fossil fuel industry, which has spent decades lying to the public about the harms of their product," said Cleetus. "The science backing the EPA's finding is rigorous and unequivocal—heat-trapping emissions pose serious threats to public health and well-being. EPA has the authority and legal obligation under the Clean Air Act to regulate sources of these pollutants, including vehicles, power plants, and oil and gas operations."
Ben Jealous, executive director of the Sierra Club, also warned that the organization "will meet [the EPA] in court" if it moves forward with the repeal.
"Lee Zeldin is willing to go so far as to break established law to pay back the corporate executives and polluters who spent millions to get Donald Trump elected," said Jealous. "This breathtakingly illegal power grab defies both the Supreme Court and Congress, and if Trump agrees to this plan, the Sierra Club will meet them in court. We will never allow any administration to sell out the climate, our health, our clean air, and our future."
Zeldin is reportedly recommending that the finding be repealed weeks after wildfires destroyed more than 12,000 homes and other buildings in the Los Angeles area and after meteorologists reported a record 143 days last year of 100°F heat or higher last year. More than 100 people were killed last year by Hurricane Helene, which damaged about 74,000 homes.
"If the Trump EPA proceeds down this path and jettisons the obvious finding that climate change is a threat to our health and welfare, it will mean more polluted air and more catastrophic extreme weather for Americans."
Experts found that the fires that devastated Los Angeles were made 35% more likely by dry, hot weather conditions and that planetary heating made Helene more dangerous and destructive.
"Any recommendation to strike the finding would be a bad-faith attempt to circumvent the law and best available science with the sole aim of boosting fossil fuel use and the profits of polluting companies," said Cleetus. "Meanwhile, people around the nation, especially in communities acutely exposed to climate impacts or pollution, will pay the price."
Dominique Browning, director and co-founder of Moms Clean Air Force, said the new reporting revealed that Zeldin "is contaminating EPA with a virulent strain of climate denial that has seized hold of many of the Trump administration's Cabinet members."
Browning noted that the EPA issued its determination in 2009 in response to the 2007 U.S. Supreme Court case Massachusetts v. EPA, which established that the agency has the authority to regulate greenhouse gases.
"EPA's action respected the ruling of the U.S. Supreme Court," said Browning. "It respected the bedrock science and respected what we all know to be true: Families across the country are experiencing the extreme weather fueled by climate emissions. With every new supercharged wildfire, hurricane, flood, and heatwave, the danger takes on a terrifying intimacy: Think of the summers that have become too hot for children to play outside, of the lifetime trauma of losing a home in a flood or fire."
"Administrator Zeldin's recommendation to strike down the endangerment finding will only bolster the billions of dollars of profit being made by the oil and gas industry—while ransacking our children's safety," Browning said.
David Doniger, senior strategist and attorney for climate and energy at the Natural Resources Defense Council, said Zeldin's reported plan "only makes sense if you consider who would benefit: the oil, coal, and gas magnates who handed the president millions of dollars in campaign contributions."
The fossil fuel industry poured nearly $450 million into Trump's campaign, and the president promised to roll back climate regulations if oil and gas companies donated heavily to him in what critics called a quid pro quo.
"This decision ignores science and the law," said Doniger. "Fifteen years ago, the EPA determined that climate pollution endangers our health and well-being. The Denali-sized mountain of scientific evidence behind that decision has only grown to Mount Everest–size since then. The courts have repeatedly upheld the EPA's legal authority and its scientific conclusions."
"This is the clearest example of the Trump administration putting polluters over people, and that's saying a lot," Doniger added. "If the Trump EPA proceeds down this path and jettisons the obvious finding that climate change is a threat to our health and welfare, it will mean more polluted air and more catastrophic extreme weather for Americans. We will see them in court."
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