Power plant greenhouse gas emissions don’t contribute significantly to ‘dangerous air pollution’

CEI recently submitted comments on the Environmental Protection Agency’s (EPA) Proposed Rule to repeal greenhouse gas (GHG) emission standards for fossil fuel power plants. The Proposed Rule has both a “primary proposal” and an “alternative proposal.” We support both proposals and encourage the EPA to finalize each one.

The alternative proposal essentially updates economic, technological, and logistical critiques made by commenters and petitioners who challenged the “best system of emission reduction” determinations underpinning the Obama administration’s October 2015 GHG emission standards for new and existing fossil fuel power plants and the Biden administration’s May 2024 GHG standards for such facilities, commonly referred to as “carbon pollution standards” (CPS).

In contrast, the primary proposal would determine that GHG emissions from US power plants do not “contribute significantly” to “air pollution which may reasonably be anticipated to endanger public health and welfare,” and consequently that such emissions lack the necessary “predicate” for regulation under Section 111 of the Clean Air Act (CAA). The primary proposal aims not only to repeal the CPS Rule’s GHG emission standards but also to forestall such regulation by the EPA in future administrations.

In this post we explain why in our view GHG emissions from the US electric sector do not contribute significantly to dangerous air pollution under the CAA.

Statutory background

“With this action,” the Proposed Rule states, “the EPA proposes to resolve a decade’s worth of regulatory uncertainty brought on by the Agency’s novel attempts to regulate GHG emissions from fossil fuel-fired power plants under CAA section 111” (90 FR 25752, 25754). The basic provisions of CAA § 111 may be summarized as follows.

CAA § 111(b) requires the EPA Administrator to list categories of stationary sources that in his judgment “cause or contribute significantly” to “air pollution which may reasonably be anticipated to endanger public health or welfare,” and to establish emission performance standards for “new” (i.e., future) sources in those categories. Such standards are called new source performance standards (NSPS).

CAA § 111(d) requires the Administrator, subject to certain exceptions, to prescribe regulations (called “guidelines”) under which each state must submit a plan to establish performance standards for “existing” (i.e., already built) sources in the same categories as those regulated by the EPA under CAA § 111(b). Such state standards are called existing source performance standards (ESPS). The Clean Power Plan (CPP), vacated by the Supreme Court in West Virginia v. EPA (2022), is perhaps the best known (or most notorious) CAA § 111(d) rule.

All CAA § 111 performance standards apply to stationary sources. CAA § 111(a) defines “stationary source” as “any building, structure, facility, or installation which emits or may emit any air pollutant.”

Per CAA § 111(a), performance standards are to reflect “the degree of emission limitation achievable through the application of the best system of emission reduction which (taking into account the cost of achieving such reduction and any nonair quality health and environmental impact and energy requirements) the Administrator determines has been adequately demonstrated.” For a best system of emission reduction to be “adequately demonstrated,” the standards based upon it must be “achievable” taking “cost” and the other factors into account.

The language quoted above from CAA § 111(a) informs the alternative proposal’s repeal of specific CPS emission performance standards. For example, the CPS Rule determined that 90-percent carbon capture and storage (CCS), installed by January 1, 2032, is the “adequately demonstrated” “best system of emission reduction” for new baseload natural gas power plants (89 FR 39798, 33903). The alternative proposal rejects that determination, and rightly so.

No commercial utility-scale natural gas CCS plant exists today. Only one small-scale facility was ever built: Florida Power & Light’s 40-megawatt CCS gas plant in Bellingham, Massachusetts. When the unit closed in 2005, Bellingham had a population of 15,750. A single, small, long-defunct natural gas CCS power plant provides no evidence that a 90-percent carbon capture system is adequately demonstrated for new natural gas power plants serving large metropolitan areas, industrial centers, and new data centers in an era of rising electricity demand.

Primary proposal

Rather than critique the NPS Rule’s technical assessments, the primary proposal challenges the Obama and Biden EPAs’ CAA § 111(b) “significant contribution” findings.

The primary proposal makes a two-step argument. First, to regulate an air pollutant under CAA § 111, the EPA must determine that emissions of that specific pollutant contribute significantly to “air pollution which may reasonably be anticipated to endanger public health or welfare” (abbreviated in the Proposed Rule as “dangerous air pollution”). Second, GHG emissions from power plants do not contribute significantly to dangerous air pollution.

The law requires a pollutant-specific determination

The EPA’s October 2015 new source power plant rule, the CPP, and the CPS Rule, asserted (or assumed) that because the EPA had already listed coal and gas power plants as source categories contributing significantly to dangerous air pollution, the agency did not need to make a pollutant-specific significant contribution finding for GHG emissions as a predicate for regulating such emissions under CAA § 111. According to those rulemakings, the only predicate the EPA needed to regulate power plant GHG emissions was a “rational basis” for doing so (80 FR 64510, 64530; 89 FR 39798, 39825).

There are obvious problems with that reasoning. CAA § 111 does not use the phrase “rational basis,” so provides no guidance as to how courts should distinguish a genuine rational basis from a plausible excuse. More importantly, the fact that a source category contributes significantly to dangerous air pollution is no guarantee that a specific type of pollutant emitted by the category contributes significantly. In a statute requiring the EPA to take cost into account, it would not be reasonable for the EPA to regulate emissions that do not contribute significantly to dangerous air pollution.

More fundamentally, the Obama-Biden interpretation is incoherent. It is impossible to judge whether a source category contributes significantly to dangerous air pollution without first analyzing the specific pollutants emitted by the category and their potential effects on dangerous air pollution.

The primary proposal may seem bold and new but in fact it restores the EPA’s original interpretation of CAA § 111(b). Pollutant-specific significant contribution findings were the very basis for the EPA’s decisions to list coal and natural gas power plants as CAA § 111 source categories in the first place. In August 1971, the EPA listed coal power plants because of the category’s significant contribution to three types of dangerous air pollution: particulate matter (PM), sulfur dioxide (SO₂), and nitrogen oxides (NO_X) (36 FR 15704). In October 1977, the EPA listed natural gas power plants because of the category’s significant contribution to two types of dangerous air pollution: SO₂ and NO_X (42 FR 53657).

Tellingly, the 1977 rulemaking for natural gas power plants expressly declined to propose new source standards for emissions of hydrocarbons (HC), carbon monoxide (CO), and PM. The EPA explained that, even at peak operating load, gas combustion turbine HC and CO emissions are “relatively low,” and PM emissions from the source category “are minimal” (42 FR 53782, 53783).

Step one of the primary proposal reasonably concludes that before the EPA may establish GHG emission standards for fossil fuel power plants, the agency must make the “predicate” finding that GHG emissions from such sources contribute significantly to dangerous air pollution (90 FR 25752, 25754).

US power plants do not contribute significantly

The primary proposal does not challenge the thesis of the EPA’s 2009 Endangerment Finding that the growing “atmospheric mix” of six anthropogenic GHGs is “air pollution” that may reasonably be anticipated to endanger public health and welfare (74 FR 64696, 64697). The issue in the Proposed Rule is narrower: Do US power plant GHG emissions contribute significantly to that dangerous air pollution?

To determine if there is a significant contribution, the Obama administration in its 2015 new source performance standards regulating GHG emissions from new power plants looked at the volume of GHG emissions from power plants. The Proposed Rule explains that the Obama EPA found “GHG emissions from domestic fossil fuel-fired EGUs ‘significantly contribute’ to dangerous air pollution based exclusively on the volume of GHG emissions from the source category” (90 FR 25752, 25767).

That was the Obama and Biden EPAs’ supposed “rational basis” and logic for regulating power plant GHG emissions. In fact, it was an arbitrary basis.

A volume threshold alone comparing domestic power plant GHG emissions to total global emissions does not tell us whether those emissions make any material difference to the “air pollution” or the danger it poses to public health or welfare. Under this volume approach, a significant contribution could be claimed even if the emissions don’t have any detectable effect on the danger level of the air pollution. Given the purpose and language of the Clean Air Act and Section 111(b), which is to protect the public’s health or welfare from dangerous air pollution, not analyzing these effects is unreasonable.

The Proposed Rule rejects “a purely quantitative measure of significance resting on the absolute volume of emissions from a source category.” Ironically, relying solely on a volume threshold would likely work in the favor of the EPA’s current argument that there is no significant contribution. After all, US electric power sector GHG emissions are steadily declining and in 2022 accounted for just three percent of total global emissions. But to its credit, the agency isn’t taking this volume-based approach.

Determining whether there has been a significant contribution requires sufficient reasoning consistent with the requirements of the statute. Section 111(b) expects the Administrator to use his judgment to figure out whether the emissions contribute significantly to dangerous air pollution. This requires assessing the effects the emissions have on air pollution that may reasonably be anticipated to endanger public health or welfare. If the emissions in no way (or in a very small way) affect the danger level from the air pollution, then it would be unreasonable to claim that the emissions contribute significantly to the dangerous air pollution.

So, how do we answer the question about the effect on danger levels?

The basic narrative explaining the potential dangers associated with the “atmospheric mix”—the global bucket of GHG “air pollution”—is well known. Rising atmospheric GHG concentration increases global temperatures, which may adversely affect weather patterns and sea levels, which may adversely affect public safety, property damage, labor productivity, GDP growth, energy costs, and other economic variables, which may adversely affect public health and welfare.

Since global warming is the first link in the chain of endangerment attributed to rising GHG concentration, the first step in determining whether US power plant GHG emissions significantly contribute to that danger is to calculate their effects on global warming.

A recent study by Brent Bennett of the Texas Public Policy Foundation offers a reasonable estimate based on conservative inputs.

• Bennett uses the US government’s standard climate-policy impacts calculator, a model called MAGICC. He runs MAGICC with its mid-range climate sensitivity estimate, namely, that each doubling of atmospheric GHG concentration increases global average surface temperatures by 3.0°C. Note, recent research suggests sensitivity “values between 1.5°C and 2°C are quite plausible.”
• He uses the UN climate panel’s mid-range baseline emission scenario, known as SSP2-4.5. Recent research suggests the world is on a lower emissions path.
• He assumes the US global share of GHG emissions (currently 13 percent) will hold steady through the end of the 21^st century, even though the US share has been declining for the past 25 years.  

Under those assumptions, MAGICC estimates that eliminating all US power plant CO₂ emissions by 2030 would avert 0.015°C of warming by 2050. Bennett calculates that 0.015°C is 10 times smaller than the uncertainty range in the UK Hadley Centre’s long-term global annual surface temperature record for 1850-2024 and less half the uncertainty range in the Centre’s temperature record for recent decades.

A temperature effect below margin of error is too small to be detected or verified. The US power sector’s contribution to global warming is, therefore, insignificant.

But if the warming effects of US power sector GHG emissions are undetectably small, even more so are the putative second and third order effects of those emissions. Therefore, US power sector CO₂ emissions do not contribute significantly to dangerous air pollution.

The question before the EPA Administrator is this: Do GHG emissions from the US electric power sector make the associated “air pollution” more dangerous in a significant way? The answer is: They do not.