Early this month, the Environmental Protection Agency filed its Reconsideration of 2009 Endangerment Finding and Greenhouse Gas Vehicle Standards in the Federal Register.1
Despite its banal title, EPA’s proposed action here is radical to its core, matched only, perhaps, by its earlier (June 17) proposal to repeal all GHG restrictions on fossil fuel-fired power plants.
Nearly two decades back, in Massachusetts v EPA (2007), the US Supreme Court declared the danger to the nation from unabated fossil fuel pollution to be “well-recognized.” Responding in 2009, in its original Endangerment Finding, EPA formally found both that GHG emissions “endanger both the public health and the public welfare of current and future generations,” and that GHG pollution from new motor vehicles and engines contributes to that endangerment.
On that basis, under the authority of Section 202 of the Clean Air Act, EPA proceeded to propose (and then promulgate) a series of restrictions on vehicle GHG emissions. It followed those rulemakings with others including, pursuant to Clean Air Act § 209, restrictions on power plant GHG emissions.
But in the space of just 45 days, EPA has issued draft repeals of all such restrictions from our nation’s two largest emitting sources: the fossil fuel-fired power plant2 sector and the transportation sector.
At least one aspect of the EPA proposal appears downright hallucinatory.
The August 1 proposed rule is poorly reasoned, and I will turn to that feature of it in an upcoming note to this space.
Here, however, I’d like to turn to an aspect of the EPA proposal that appears to be downright hallucinatory. That is, EPA’s refrain — repeated in one or other form 12 times in its proposed repeal — that back in 2009 the EPA had exceeded its authority when it “defined the air pollution” it sought to restrict as “the combined elevated global concentrations in the upper atmosphere of six ‘well-mixed GHGs, CO2, methane, N2O, HFCs, PFCs, and SF6.”
One problem with EPA’s formulation is that in its 2009 Endangerment Finding, the Agency did not refer at all to “the upper atmosphere.” Not even once. And for good reason, perhaps.
As the National Oceanic and Atmospheric Administration (NOAA) explains, the term “upper atmosphere” refers to the thermosphere—the portion of the atmosphere lying “[b]etween about 53 miles (85 km) to 375 miles (600 km)” above Earth’s surface. The thermosphere lies above what is considered the middle atmosphere—the mesosphere (31 miles (50 km) to 53 miles (85 km) above Earth’s surface) and the stratosphere (4 -12 miles (6-20 km) to “around” 31 miles (50 km) above the planet).3
But as John Birks — atmospheric scientist and CPR Initiative Board Member — recently explained to me:
About 90% of air molecules and thus CO2 is within the troposphere (below about 15 km at midlatitudes and where weather occurs). Infrared radiation absorbed by CO2 from Earth’s IR emission is re-emitted and reabsorbed by these low-lying CO2 molecules. As you go higher in altitude, the concentration declines to the point that emitted IR can escape being absorbed by CO2 (and water vapor and other GHGs) and be lost to space. This occurs in the upper troposphere/lower stratosphere.
“As for the “upper atmosphere,” using the U.S. Standard Atmosphere (1976) tables, the pressure at 85 km is 0.373 Pa (≈ 3.73×10⁻³ hPa). Sea-level pressure is 101325 Pa. So, the fraction of air molecules (and thus, atmospheric CO2) above 85 km is 0.373/101325 = 3.68 e-6. [Accordingly] more than 99.999% of CO2 emitted to the atmosphere remains below the upper atmosphere.
In a follow-up email, John confirmed that the vanishingly small quantity that reaches and remains in the upper atmosphere accounts for a vanishingly small quantity of warming.
Why in the world, then, has the present EPA, in its August 1 proposed repeal, chosen to repeatedly and falsely characterize the object of the Agency’s concern way back in 2009 as “elevated global concentrations of GHGs in the upper atmosphere”? My own theory is that EPA’s beleaguered writers were struggling to construct a distinction between pollution whose control they purport exceeds the Agency’s jurisdiction under the Clean Air Act, and pollution which is within the Agency’s purportedlyl traditional concern — that is, pollution that endangers health and welfare “directly” through “local or regional exposure.”
In devising these direct/ indirect and local/ global distinctions EPA is really up the wall, legally, because the actual terms of the Clean Air Act simply provide zero support for them. But the Agency’s determination to press these distinctions may help explain its dogged mischaracterization of what it targeted in its 2009 Endangered Finding. We will have occasion to return to these topics as soon as next week.
- 90 FR 36288 (August 1, 2025). ↩︎
- EPA, Repeal of Greenhouse Gas Emissions Standards for Fossil Fuel-Fired Electric Generating Units, 90 FR 25752 (June 17, 2025) . See our recent Unwarranted: The Case Against Repeal of those power plant GHG restrictions. ↩︎
- NOAA, Layers of the Atmosphere at https://www.noaa.gov/jetstream/atmosphere/layers-of-atmosphere. ↩︎
*With apologies to Mary Poppins wherein it was urged of the children and others to go fly a kite
“Up through the atmosphere, up where the air is clear.”
Please note: You can submit your own comments. EPA’s deadline is September, 22, 2025. Comments may be submitted is any of several ways:
- Via EPA’s Federal eRulemaking Portal: https://www.regulations.gov/. Follow the online instructions for submitting comments.
- Via email to: a-and-r-Docket@epa.gov. Include Docket ID No. EPA–HQ–OAR– 2025–0194 in the subject line of the message.
- By Mail: U.S. Environmental Protection Agency, EPA Docket Center, OAR Docket, Mail Code 28221T, 1200
Pennsylvania Avenue NW, Washington, DC 20460.