The Endangerment Finding: A Deep Dive

Hey,

This piece was contributed by Stu Nissenbaum, with editorial overlay from Nick. Stu is a climate policy leader and former U.S. Environmental Protection Agency (EPA) insider who helped ensure that the strongest available science underpinned major federal emissions rulemakings during the Biden Administration; the U.S. greenhouse gas endangerment finding served as the scientific foundation for the majority of the standards he worked on. 

At the EPA, he operated at the intersection of science and policy, guiding technical analyses and advising senior leadership on landmark emissions standards, including federal vehicle emissions standards, power plant rules, and oil and gas methane regulations. He also served as Head of Delegation to the Arctic Council’s Arctic Contaminants Action Program, representing the United States in advancing international cooperation on pollution reduction. In addition, he is a member of the Science Alliance at Protect Our Winters and teaches as an adjunct professor. 

Stu is actively seeking senior leadership roles and welcomes conversations with organizations looking for experienced, science-grounded climate leadership.

Much of the climate field is reeling following the Trump Administration's repeal of the 2009 Greenhouse Gas (GHG) Endangerment Finding. My LinkedIn is flooded with statements from various organizations and personal posts with thoughts and feelings about the repeal. Generally, they are pretty dire. I get it…it’s bad. I would know–I worked on emissions rulemaking at the EPA for close to five years, predominantly under the Biden Administration. Unfortunately, my office barely exists there anymore, and I remain unemployed (shameless plug for anyone hiring). The Endangerment Finding underpinned everything I worked on, including the Power Plant Rules, the Oil and Gas Methane Rules, and the Vehicle Emissions Standards for Light-, Medium-, and Heavy-Duty Vehicles. It’s an incredibly important rule. So let’s talk about it.

What is the GHG Endangerment Finding?

In 2007, Massachusetts v. EPA was brought before the Supreme Court. This case contended that because the Clean Air Act covered “ [any] air pollutant” that “could endanger public health or welfare,” carbon dioxide and other GHGs should be regulated. In a 5-4 decision, the Supreme Court found in favor of Massachusetts and eleven other states that GHGs can and should be regulated under the Clean Air Act.

The initial court case was brought on the basis of vehicle emissions, but the decision established the law, creating jurisdictional and regulatory implications for other industries as well. The GHG Endangerment Finding was established in 2009 under the first Obama Administration. It was lauded as a major climate victory, as it concluded that six major GHGs (CO2, methane [CH4], NOx, HFCs, PFCs, and SF6) threatened public health and welfare and should be regulated under the Clean Air Act (some short-lived greenhouse gasses that would be more impractical to regulate, like water vapor, were excluded). For seventeen years, the Endangerment Finding underpinned most of the EPA's climate regulations. 

The Endangerment Finding’s legacy

Specifically, the Endangerment Finding served as the legal foundation for federal climate regulation since 2009, and its effects now extend across a wide range of regulatory programs and economic sectors. Most directly, the finding enabled the EPA to regulate GHG emissions from motor vehicles under the Clean Air Act. This authority has shaped vehicle emissions standards for passenger cars and heavy-duty trucks for more than a decade and played a central role in driving automaker investment in electrification, battery manufacturing, and low-emissions vehicle technologies. These standards have also supported compliance credit markets and long-term product planning across the automotive sector.

The finding also triggered EPA’s authority to regulate greenhouse gas emissions from stationary sources such as power plants, refineries, and industrial facilities. Once GHGs became regulated pollutants under the Clean Air Act, major new and modified facilities became subject to permitting requirements that require the use of best available control technology to limit emissions. The finding also underpins EPA’s authority to establish performance standards for carbon dioxide emissions from power plants, which have been a central component of federal climate policy over the past decade. These regulatory authorities have influenced infrastructure investment, accelerated coal plant retirements, and shaped the design and economics of new energy and industrial projects.

Beyond direct regulation, the Endangerment Finding enabled the development of federal greenhouse gas reporting systems, emissions inventories, and analytical tools that are now embedded in regulatory decision-making and private sector planning. Programs such as EPA’s greenhouse gas reporting program provide essential data used by regulators, investors, and companies to track emissions and assess risk. The finding has also supported the use of climate damages in federal cost-benefit analysis, which affects a wide range of regulatory actions beyond traditional environmental rules, including appliance efficiency standards, infrastructure planning, and energy policy.

Further, the finding had important implications for state climate policy and broader market behavior. States have relied on the federal regulatory framework to implement their own vehicle standards, industrial regulations, and decarbonization policies. At the same time, the existence of durable federal authority to regulate greenhouse gases has shaped long-term capital allocation decisions across the energy, transportation, and industrial sectors. Investors and companies have made strategic decisions based on the expectation that greenhouse gas emissions would remain subject to regulatory constraint. After seventeen years, the Endangerment Finding should thus be seen not as an isolated regulatory determination but a central legal pillar supporting the structure of federal climate regulation and the economic systems that developed around it.

The repeal

To be sure, the most recent announcements aren’t new news. The EPA Administrator, Lee Zeldin, announced that the EPA was working to repeal the finding back in August of last year. Many organizations wrote letters and testified during the comment period, including one of my favorite organizations, Protect Our Winters, which sent a petition to The Outdoor State for support and whose CEO, Erin Sprague, testified. However, knowing the priorities and having followed the actual decision-making and behavior of the current administration, I do not believe anyone is truly shocked.

The Trump Administration says it repealed this finding because it creates excessive regulation and harms business. They also want to tout it as the largest deregulation action in history, with a stated purpose of “reigniting the American Dream.” More broadly, this action reflects a shift toward a purported “energy dominance” framework that prioritizes maximizing domestic fossil fuel production and limiting federal regulatory constraints on GHGs to unlock greater energy production capacity in general, across all generation sources, including coal, and except for wind, which the President hates particularly for peculiar and perhaps past pecuniary reasons. 

Insofar as the Endangerment Finding has served as the legal predicate for regulating GHGs under multiple Clean Air Act provisions, including mobile-source standards under Section 202 and stationary-source standards under Section 111, removing this predicate weakens the EPA’s ability to impose emissions performance standards that would otherwise continue to drive fuel switching and accelerated electrification. A robust decarbonization framework and the energy transition rely on these regulatory authorities, alongside statutory incentives such as those in the Inflation Reduction Act, to internalize the external costs of GHG emissions and shift investment toward lower-carbon technologies. Hence, this action represents both a discrete regulatory change and a structural shift in the federal government’s role in (or, really, its abdication of a large part of its role in) shaping long-term emissions trajectories.

The administration also relied on its own DOE report titled A Critical Review of Impacts of Greenhouse Gas Emissions on the U.S. Climate, which suggested that increased carbon dioxide in the atmosphere could have a “greening effect.” This “greening effect” implies that increasing atmospheric carbon dioxide concentrations will boost vegetation growth. This premise is largely rejected by the scientific community and relies on a report that a judge ruled violated transparency laws in the development and operation of the working group. Even if we accept (as we should) that higher atmospheric carbon dioxide concentrations can yield more plant growth locally or in some parts of the world, focusing on that spatially limited dynamic misses the forest for the trees vis-à-vis the extent to which climate change at large risks destabilizing ecosystems and dramatically dysregulating Earth’s climate system in general.

Where do we go from here?

State and federal policies

Not all federal GHG regulations depend on the Endangerment Finding. For example, the American Innovation and Manufacturing (AIM) Act of 2020 explicitly directs EPA to phase down hydrofluorocarbons (HFCs), according to a statutory schedule. This authority is independent of any endangerment determination, and EPA’s obligations under the AIM Act will remain in force regardless of future litigation over broader GHG regulatory authority.

In addition, Congress anticipated potential legal challenges to EPA’s GHG regulatory authority when it enacted the Inflation Reduction Act (IRA). Title VI of the IRA amended the Clean Air Act (CAA) to explicitly define six greenhouse gases as “air pollutants.” This statutory clarification may provide an alternative legal basis for the EPA to regulate GHG emissions under the CAA without relying on the finding, although this theory has not been fully tested in the courts.

States also retain broad and durable authority to regulate greenhouse gas emissions and can continue to play a central role in climate policy, particularly if federal regulatory efforts remain constrained. State governments have clear authority over many major sources of emissions, including transportation fuels, electricity generation, industrial sources, buildings, and natural gas systems. When federal regulation weakens or stalls, states have historically stepped in to advance decarbonization through regulation, infrastructure investments, and market-based policies. Opportunities for state leadership are perhaps more pronounced now than ever.

Litigation

I do not believe that the repeal of the Endangerment Finding will officially take hold anytime soon. There will be months and maybe even years of litigation surrounding this repeal. The repeal flies in the face of Massachusetts v. EPA, i.e., it’s in conflict with the established law of the land. The AGs from several states have already said they will litigate the decision, and I am sure several climate-focused organizations will follow suit. Indeed, many are preparing to or have already filed suit. The litigation may even carry into the next administration, at which point this could all be moot depending on which way the political pendulum swings. Additionally, judicial stay orders and injunctions on this repeal will likely prevent the EPA from using it to justify its deregulation agenda. That said, even if the Endangerment Finding survives, the whiplash from all this back-and-forth is deleterious to business, policymaking, and public confidence both domestically and abroad, to say nothing of climate change and efforts to address it in general. 

The private sector and consumers

Despite the last year of deregulation and attacks on climate policy, the climate field is still burgeoning. In the last few years, there has been increased discussion of superpollutants (i.e., most other greenhouse gasses beyond carbon dioxide), a topic Nick has written about several times and himself beat the drumbeat for. Companies and organizations are finding ways to continue to reduce these emissions. Just look at companies like Tradewater, which caps orphaned wells to cut methane and dispose of old HFC and HCFC refrigerants. The work is already being done, and it advances by the day.

Climate also remains front-of-mind for consumers. Here in Colorado, we are facing one of our worst (read as warmest) winters ever. The mountains have minimal snowpack, and in Denver, roughly half of our winter days have featured temperatures above 60° F. The whole country has experienced unusual weather patterns, reinforcing the idea that climate change is not just about global warming but about climate system dysregulation. In parallel, battles over data centers are becoming commonplace in townships, cities, and counties across the country, as consternation over rising electricity prices, water usage, and more comes to the fore. 

Arguably, the whims of the Trump Administration are a drop in the bucket compared to the totality of the diverse, global set of climate change drivers. China alone accounts for roughly three times as many carbon dioxide emissions annually as the U.S. does at this point, a gap that is likely to widen even further into the rest of this decade and next. Still, this is not to make light of the potential loss of the Endangerment Finding. To quote from “The Long Heat,” a recently released book by Wim Carton and Andreas Mann, in many ways:

Pursuant to that final question, diverging even more flagrantly from an even close to adequate mitigation and adaptation path is certainly not the answer. There is already too little ground of concrete action on which to stand to cede any further. As such, especially with respect to important statutes like the Endangerment Finding, there can really be no acceptance or acquiescence. Prescribing action, while essential, is difficult, especially when addressing individuals like you. You can support any of the many organizations, including but not limited to the Natural Resources Defense Council (NRDC) and the Environmental Defense Fund (EDF), which mobilize to both litigate and navigate other policy avenues to mitigate the harms of this and other repeals and steps backward on climate action to which we’ve been routinely subjected. Really, the answers come back to staying in the game, a concept that is necessarily amorphous to who you are and your experience, but that boils down to finding your own best individual and organizational wedges to influence things, including and beyond yourself. You’re always welcome to reply to the email if you need more inspiration.

Take a deep breath

Finally, as this header says, take a deep breath. I am by no means trying to minimize the impact that this repeal could have, but the best we can do is to keep on keeping on. Part of the Trump Administration’s strategy is to demoralize and to divide; resisting that isn’t easy, but resisting those dynamics is an essential element of the resistance itself. It is easy to get caught up in sensationalizing bad news.  As someone who has worked in government for years, despite how fast things seem to move, they are actually way slower, nuanced, and little is ever entirely lost.

Hope this offers some deeper insight into what’s been going on with the Endangerment Finding. To connect with Stu and offer thoughts, feel free to respond directly to this email.

— Nick