The Scientific Foundation of the 2009 Finding

The 2009 endangerment finding did not emerge from ideology. It resulted from evidence about the climate effects of greenhouse gases—mountains of it, accumulated over decades by atmospheric scientists, public health researchers, and climatologists whose work was peer-reviewed, replicated, and confirmed across independent institutions worldwide. The scientific consensus on anthropogenic climate change is robust.

To reverse a regulatory finding grounded in that consensus, the EPA must either produce superior science or rely on something else entirely. In eliminating the endangerment finding, it did the latter: used a sequence of legal arguments so strained, so internally inconsistent, and so contrary to established precedent that it suggests a government agency less interested in scientific truth and environmental protection than in delivering a predetermined political outcome. This follows a pattern seen at other federal regulatory agencies that on occasion have adopted a policy formulation strategy of “Here’s what we want to do, now let’s find a rationale.” Several of these have been overturned by the courts as arbitrary and capricious.

The withdrawal of the endangerment finding appears to run directly counter to the Supreme Court’s landmark 2007 ruling in Massachusetts v. EPA, which held that greenhouse gases are air pollutants under the Clean Air Act (CAA) and the EPA has a legal obligation to determine whether they endanger public health. The agency’s recent reversal does not merely sidestep that ruling, it constructs elaborate justifications for why it no longer applies, an exercise that legal scholars have found difficult to defend.

Five Dubious Arguments

The EPA has offered five primary arguments for rescinding the endangerment finding. Each one has difficulty surviving scrutiny.

Redefining “air pollutant” / The first and perhaps most tenuous argument is that the term “air pollutant” under CAA Section 202(a) covers only substances that cause harm through direct exposure—what the agency calls “local and regional” pollutants—and therefore excludes greenhouse gases, which cause harm indirectly through atmospheric warming. This interpretation imposes a definitional restriction not found in the statute. The CAA defines “air pollutant” expansively, covering any substance emitted into or entering the air, without regard to the mechanism of harm. The EPA’s effort to read in a harmful-by-proximity requirement is, in effect, legislating through interpretation rather than through clear congressional intent.

More damaging still, the agency’s argument collapses on its own terms, as many greenhouse gases also cause harm through direct exposure. Methane causes direct harm when inhaled in concentrated amounts. Carbon dioxide drives ocean acidification with measurable negative consequences for human health, food security, and coastal communities. And the CAA itself defines public welfare to include “weather, visibility, and climate,” terms that go well beyond direct-exposure effects.

Thus, the EPA is not applying science when making this argument. It is retrofitting a legal theory around a conclusion already reached for other reasons.

Demanding an impossible causal chain / The second argument is equally tortured. Section 202(a) explicitly applies to motor vehicle emissions, as they are a large source of air pollutants. The EPA now insists that, to justify regulation, these emissions must be evaluated in isolation and by vehicle subcategory to determine that they independently cause significant harm. This is not how atmospheric science works. Climate change is an inherently cumulative phenomenon: No single type of emission source, no single nation, and no single category of vehicles (e.g., gasoline-powered) triggers warming in isolation. Harm arises from the collective weight of global emissions accumulating over time. The EPA knows this. Its own scientists know this. Yet the agency has constructed a legal standard that demands what atmospheric physics cannot deliver: a clean, isolated causal chain from one vehicle category to a measurable global outcome.

The implications of this standard are important. As University of California, Berkeley, law professor Daniel Farber has observed, applying this logic consistently would mean that a pollutant responsible for 1 percent of US annual mortality would face no regulatory scrutiny whatsoever. One percent of approximately three million annual US deaths amounts to 30,000 people, a figure that no serious public health framework would dismiss as insignificant. Yet, political appointees can dismiss 1 percent as insignificant under the law and thus not subject to regulation.

The EPA’s own data reveal that transportation is the highest-emitting sector in the United States, which in turn is the world’s second-largest greenhouse gas emitter. Describing this contribution as too insignificant to warrant regulation is not a scientific judgment; it is a political one disguised as scientific.

There is also a troubling procedural inconsistency embedded in this argument. The EPA has applied its new linkage requirement exclusively to greenhouse gases while claiming that its regulations on conventional pollutants—which do not follow this new template—will remain unaffected. Arguably, if the principle holds, it must hold across all pollutants.

Overreading the major questions doctrine / Third, the EPA invokes the Supreme Court’s “major questions doctrine”—established most recently in West Virginia v. EPA (2022)—as though it constitutes a blanket prohibition on climate regulation. The major questions doctrine is a principle of statutory interpretation that the Supreme Court has used to limit federal agency authority. The core idea is that when an administrative agency claims the power to make a decision of vast economic or political significance, the Court will require Congress to have clearly and explicitly granted that authority rather than inferring it from ambiguous or broadly worded statutory language. As Chief Justice John Roberts wrote in the majority opinion:

In certain extraordinary cases…, something more than a merely plausible textual basis for the agency action is necessary. The agency instead must point to clear congressional authorization for the power it claims.

The Court applied this doctrine narrowly in West Virginia v. EPA, targeting the scope of one specific regulatory approach. In Utility Air Regulatory Group v. EPA (2014), the Court struck down one portion of a climate regulation under an earlier version of this doctrine while simultaneously upholding another portion of the same regulation. The agency’s sweeping reading of these precedents—treating them as categorical barriers to any greenhouse gas regulation—is dubious. It is motivated reasoning in search of a legal rationale.

Trivializing catastrophic harm / Fourth, the EPA argues that US vehicle greenhouse gas emissions are simply too insignificant to warrant regulation, accounting for only about 1 percent of global warming by its own estimate. But significance is context-dependent, and the context here is a harm of planetary scale. The social cost of carbon—the economic value assigned to the damage caused by each metric ton of carbon dioxide or equivalent greenhouse gas emission—is substantial by virtually any serious economic accounting. A rough calculation based on the EPA’s own figures suggests that the agency’s “insignificant” 1 percent contribution, measured over the multi-decade time horizon the agency employs, yields climate costs roughly comparable in magnitude to the regulatory costs the EPA now characterizes as “immense.” By withdrawing the endangerment finding, the agency has, in effect, dismissed a harm it simultaneously acknowledges is enormous.

Fabricating a cost argument / Fifth, the EPA warns of “trillions of dollars” in costs to manufacturers and consumers from regulating these emissions. This claim is partly undermined by the agency’s own fact sheet, which describes a total cost of $1.3 trillion from 2027 to 2055. Moreover, the EPA’s own analysis found that rescinding the endangerment finding would cost consumers nearly $1.5 trillion in increased maintenance and repair expenses over the same period because gasoline-powered vehicles are substantially more expensive to maintain than their electric counterparts. Thus, by the agency’s own arithmetic, the endangerment finding would result in net savings to Americans.

An Institutional Crisis of Integrity

At the heart of these arguments is a familiar problem: an agency that has, under various administrations and amid various controversies, sometimes subordinated scientific rigor to political preference. In this case, rather than quietly adjusting regulatory timelines or softening enforcement priorities, the EPA has constructed an elaborate legal architecture specifically designed to justify abandoning what it knows the science supports. The agency’s watchdog reports have previously documented institutional failures in grant management and crisis response, in instances ranging from Flint, Michigan’s contaminated water supply, to delays in hazardous waste site remediation. I have written for decades about the EPA’s unscientific, innovation-stifling regulation of biotechnology. The endangerment finding reversal adds a new and more consequential chapter to that record.

The arguments the EPA has now advanced for its deregulatory action deserve engagement on both their legal and scientific merits. Serious people can debate the appropriate scope of agency authority, the proper reading of the major questions doctrine, and the right mechanisms for Congress to authorize transformative climate policy. Those are legitimate conversations. But engaging them seriously requires good-faith analysis, not the systematic dismantling of an evidentiary record that has only grown stronger in the 17 years since the original finding was issued.

Policy Should Be Based on Science, Not Politics

Science should not have to compete with political expedience. Atmospheric greenhouse gas concentrations do not adjust themselves to accommodate regulatory preferences; rather, the opposite is—or should be—true. The 2009 endangerment finding was not a political document; it was a scientific determination grounded in evidence amassed by researchers across the globe and confirmed by every major scientific institution that has examined the question.

An agency that turns its back on that evidence does not merely abandon a regulation. It abandons its reason for existing. When the EPA once again fails to let science inform policy and instead lets policy dictate its own version of “science-based regulation,” the public health of every American is left less protected, and the institutional credibility that makes environmental regulation possible at all is eroded.