US EPA has denied four petitions
challenging the Agency’s 2009 determination that emissions of greenhouse gases to the air endanger human health.
The Clean Air Act, amended in 1990, authorizes US EPA to regulate air pollution “which may reasonably be anticipated to endanger public health and welfare.” The Clean Air Act requires EPA to make determinations about the public health implications of air emissions from stationary sources (e.g., power plants) and mobile sources (e.g., cars and trucks).
EPA’s 2009 Endangerment Finding relates to six “long-lived and directly-emitted” greenhouse gases:
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Hydrofluorocarbons (HFCs)
- Perfluorocarbons (PFCs)
- Sulfur hexafluoride (SF6)
The 2009 Endangerment Finding paved the way for EPA to regulate GHGs under various Clean Air Act programs. Today, EPA requires industrial facilities that emit certain pollutants to report through the Greenhouse Gas Reporting Program or GHGRP.
A forthcoming proposed rule would amend the GHGRP to update calculation and monitoring methods and require reporting of additional data, among other revisions (Fact Sheet
In April 2022, EPA released the latest Inventory of US Greenhouse Gas Emissions and Sinks.
The result of EPA denying these petitions is that the 2009 Endangerment Finding remains in place.
Landmark EPA and Supreme Court actions related to greenhouse gases since 2000 include:
 EPA Denies Petition to Regulate GHGs
In 2003, EPA denied a petition for the agency to regulate greenhouse gases from motor vehicles. Greenhouse gases did not satisfy the Clean Air Act criteria for “air pollutants,” EPA said at the time.
Many disagreed with EPA’s decision. Before long, the Supreme Court was asked to weigh in.
 Massachusetts vs. EPA
In the 2007 case Massachusetts v. EPA,
the Supreme Court ruled that greenhouse gases “fit well within the Clean Air Act’s definition of air pollutant.”
Because GHGs are an air pollutant, US EPA has a legal responsibility to judge whether greenhouse gases contribute to climate change. EPA’s mandate to regulate air pollution is broad, partly by design. As one Supreme Court Justice put it in the 2007 decision:
“While Congress…might not have appreciated the possibility that burning fossil fuels could lead to global warming, they did understand that without regulatory flexibility, changing circumstances…would soon render the Clean Air Act obsolete.”
- Justice Stevens (Opinion dated April 2, 2007)
 Greenhouse Gas Endangerment Finding
The Supreme Court decision Mass. v. EPA required EPA to consider greenhouse gases as an air pollutant.
After completing the legal process to reach a determination, EPA decided that—yes, greenhouse gases do contribute to climate change. Therefore, they endanger human health and welfare and must be regulated under the Clean Air Act. This led EPA to create stricter fuel economy standards for motor vehicles.
The determination was upheld in 2012.
[2011—2014] GHGs and Title V Permitting
In 2011, the EPA “tailored” the definition of “major source” under both the Title V Permitting and Prevention of Significant Deterioration (PSD) programs so that only sites with the Potential to Emit (PTE) greater than or equal to 100,000 tons per year of greenhouse gases would be subject to the permitting requirements.
On June 23, 2014, the Supreme Court decided that the EPA did not have the authority to change the definition of “major source” for one group of pollutants, but that PSD permits based on emissions of Clean Air Act “criteria pollutants” could continue to require limits on GHG emissions based on Best Available Control Technology (BACT).
EPA has made recommendations to state permitting authorities for how to incorporate GHG emissions controls into PSD and/or Title V permits.
In 2016, EPA proposed action revise Title V and PSD permitting to align with the courts' decisions on greenhouse gases. As of now, no final action has been taken.
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