What is the Scientific Threshold for GHG Endangerment?
It is much lower than you think
Consider the following claims:
[E]missions are increasing the concentration of CO2 in the atmosphere through a complex and variable carbon cycle, where some portion of the additional CO2 persists in the atmosphere for centuries. . . Carbon dioxide also acts as a greenhouse gas, exerting a warming influence on climate and weather . . .
Today, I explain why the acceptance of just these claims provides a sufficient basis under the U.S. Clean Air Act (CAA) to find that greenhouse gas emissions (GHGs) endanger public health or welfare. The quote above comes from the executive summary of the much-discussed report of the Department of Energy’s Climate Working Group (DOE CWG).
“Endangerment” is a legal concept, not scientific, which can be traced back to 1955 in federal legislation regulating air pollution.1 The relevant language of the CAA is shown below, from Section 202(a), with the endangerment clause highlighted.
The concept of “endangerment” under the CAA has been considered explicitly by the courts, which concluded that “endangerment” means “risk of harm”:
The meaning of "endanger" is not disputed. Case law and dictionary definition agree that endanger means something less than actual harm. When one is endangered, harm is threatened; no actual injury need ever occur. Thus, for example, a town may be "endangered" by a threatening plague or hurricane and yet emerge from the danger completely unscathed. A statute allowing for regulation in the face of danger is, necessarily, a precautionary statute. Regulatory action may be taken before the threatened harm occurs; indeed, the very existence of such precautionary legislation would seem to demand that regulatory action precede, and, optimally, prevent, the perceived threat.2
In the 2009 EPA Endangerment Finding, the EPA administrator characterized the finding explicitly in terms of “risk of harm,”3 with the nature of risk and of harm considered together. The EPA administrator found,
. . . that six greenhouse gases taken in combination endanger both the public health and the public welfare of current and future generations.
The EPA administrator explained:
The Administrator reached her determination by considering both observed and projected effects of greenhouse gases in the atmosphere, their effect on climate, and the public health and welfare risks and impacts associated with such climate change. The Administrator’s assessment focused on public health and public welfare impacts within the United States. She also examined the evidence with respect to impacts in other world regions, and she concluded that these impacts strengthen the case for endangerment to public health and welfare because impacts in other world regions can in turn adversely affect the United States.
The CAA offers no standards of risk or harm necessary to constitute a finding of endangerment, and the Supreme Court has ruled that relatively small amounts of pollution are not exempt from regulation.4
In 2009, EPA relied on legal precedent that concluded in the context of the CAA that judgments of “risk of harm” are made on a case-by-case basis:
Ultimately, of course, whether a particular combination of slight risk and great harm, or great risk and slight harm, constitutes a danger must depend on the facts of each case.
It is significant that in some sections of the law, the CAA modifies “endangerment” and refers more precisely to and “imminent and substantial endangerment to public health or welfare, or the environment.” Under Section 202(a), the CAA uses the much broader definition of “endangerment,” without suggesting a timing or qualitative magnitude. That indicates that Congressional intent was to establish a low bar for endangerment under Section 202(a), which is also supported by the law’s legislative history.
In the majority decision of Massachusetts vs. EPA (2007), which determined that GHGs are pollutants as defined under Section 202(a), Justice Stevens explained what would be necessary to overturn a GHG endangerment finding (emphasis added):
Under the clear terms of the Clean Air Act, EPA can avoid taking further action only if it determines that greenhouse gases do not contribute to climate change or if it provides some reasonable explanation as to why it cannot or will not exercise its discretion to determine whether they do.
Given that EPA made a finding of endangerment in 2009, the second half of the sentence above is moot. The GHG endangerment finding exists.
Justice Stevens also explains why a finding of endangerment does not compel the exact parameters of regulatory action, which are necessarily subject to evaluation under additional criteria, notably costs and benefits of proposed regulations:
If EPA makes a finding of endangerment, the Clean Air Act requires the agency to regulate emissions of the deleterious pollutant from new motor vehicles. (stating that “[EPA] shall by regulation prescribe … standards applicable to the emission of any air pollutant from any class of new motor vehicles”). EPA no doubt has significant latitude as to the manner, timing, content, and coordination of its regulations with those of other agencies. But once EPA has responded to a petition for rulemaking, its reasons for action or inaction must conform to the authorizing statute.
In 2008, under the administration of George W. Bush, the EPA followed up the verdict of Massachusetts vs. EPA by noting the vast consequences that would follow from GHG regulation, even starting just with tailpipe emissions from new cars:
[I]t has become clear that if EPA were to regulate greenhouse gas emissions from motor vehicles under the Clean Air Act, then regulation of smaller stationary sources that also emit GHGs—such as apartment buildings, large homes, schools, and hospitals—could also be triggered. One point is clear: The potential regulation of greenhouse gases under any portion of the Clean Air Act could result in an unprecedented expansion of EPA authority that would have a profound effect on virtually every sector of the economy and touch every household in the land.
Feature or flaw? No doubt people views of the desirability of having EPA regulating every sector of the economy will differ.
It is important to point out that the CAA does grant the EPA administrator “emergency powers” to shut down polluting activities, when the administrator finds “an imminent and substantial endangerment” — for GHGs that would mean the ability to outlaw the burning of fossil fuels (emphasis added):
Notwithstanding any other provisions of this Act, the Administrator upon receipt of evidence that a pollution source or combination of sources (including moving sources) is presenting an imminent and substantial endangerment to public health or welfare, or the environment, may bring suit on behalf of the United States in the appropriate United States district court to immediately restrain any person causing or contributing to the alleged pollution to stop the emission of air pollutants causing or contributing to such pollution or to take such other action as may be necessary.
President Trump has declared nine (and counting) national emergencies this year. What happens if a future president decides to declare a “national climate emergency” and then decides to just stop oil? Farfetched? Maybe. Maybe not.
Back to the science — What then should we make of the DOE CWG report and the excessive and over-the-top response to it?
The DOE CWG report actually supports the EPA’s endangerment finding as a matter of the legal threshold established and adjudicated under the CAA. In fact, there is no possible scientific report or assessment that could justify overturning the finding. The fate of the planet is not at stake due to the DOE CWG report, as some would have it.
A more realistic interpretation is that the DOE CWG report and the many responses to it are about power — which experts have a voice in the public discussions that inform climate policy more broadly.
That is the conclusion I draw from how the CWG ends their report:
This report supports a more nuanced and evidence-based approach for informing climate policy that explicitly acknowledges uncertainties. The risks and benefits of a climate changing under both natural and human influences must be weighed against the costs, efficacy, and collateral impacts of any “climate action”, considering the nation’s need for reliable and affordable energy with minimal local pollution. . . An approach that acknowledges both the potential risks and benefits of CO2, rather than relying on flawed models and extreme scenarios, is essential for informed and effective decision-making.
This would seem to be just common sense. The kvetching climate scientists should take the win for the EPA endangerment finding and then demostrate to the world their openness to colleages with whom they have some disagreements. Turn down the heat.
I remain hopeful that some leaders in the climate science community realize that science and policy will both be made more robust by building a bigger tent characterized by intellectual hospitality. The EPA endangerment finding should be updated, as it is well out-of-date, to help inform future regulation grounded in the best available science.
Ultimately, reconsideration of the EPA GHG endangerment finding will be determined based on law, not science. Under existing law, it is of course conceivable (if not likely) that the Roberts court overturns the finding on legal grounds. Whether they do so or not won’t make much difference to U.S. energy policy or emissions.
U.S. energy and climate policy would benefit from the certainty and precision that would come from amending the CAA to include a new section on GHGs, following the precedent of the 1991 CAA amendments which created a new section of the law for ozone-depleting substances — but that is a topic for another day.
You are invited—> Should the EPA’s Greenhouse Gas Endangerment Finding Be Reversed? A public forum at AEI with me and four other excellent panelists in Washington, DC, September 17th, 9am ET. You can register to attend in person or watch via Zoom at this link. I can promise a diversity of views along with informed and respectful debate — as it should be.
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Note that “danger” and “endangerment” are used interchangeably.
Ethyl Corporation v. Environmental Protection Agency, etc. 541 F.2d 1 (D.C. Cir. 1976)
The word “risk” appears 237 times across the 52-page document.
That means that arguments against the endangerment finding based on the (true) claim that U.S. new vehicles contribute only a tiny amount of GHGs in global context are unlikely to pass legal muster.
Very good post and very illuminating. You write:
"...taking further action only if it determines that greenhouse gases do not contribute to climate change..."
We see the flaw is really in the Clean Air Act, which is a poster child of the impact of a poorly written law. Literally anything, even breathing, can be banned. Reading the law literally, the government could end civilization and kill all of us in the name of saving what?
Let us hope that the EPA and Lee Zeldin win, I don't see any way Congress will fix the law. The law itself is dangerous.
So, under the current standard, endangerment =risk of harm, without the consideration of offsetting benefits. Given those parameters, I am forced to recommend that we add oxygen to the list. It enables destructive wildfires, allows internal combustion engines to pollute the atmosphere and, I am told, Donald Trump consumes oxygen to carry out his MAGA agenda.