Environmental Protection Agency (EPA) power plant regulations finalized in 2024 provide most of their carbon-reducing benefits through the accelerated retirement of coal plants, a new analysis finds. The regulations could reduce emissions from the power sector by 51% in 2040 compared with 2022 levels, almost double the 26% reduction that would occur without the rules, the research finds.
The rules could be strengthened further by tightening emissions for older natural gas plants, according to the new research. But the Trump administration has signaled that it will move to roll back the new regulations, raising questions about whether any of the climate benefits will be realized.
“This work can provide some quantitative analysis on how much we will lose if we lose this rule,” says Qian Luo, a postdoctoral research associate at Princeton Univ. who coauthored the study along with Princeton assistant professor and energy systems engineer Jesse Jenkins.
Clean Air Act
The EPA regulations — enacted under Section 111 of the Clean Air Act — are complex, with multiple options available to enable power plant operators to reach emission reduction requirements. They also vary by class of generator. For example, the regulations require the retirement of coal plants by 2038 or the institution of 90% carbon capture and storage by 2032. Coal plants slated for retirement before 2039 must begin co-firing with 40% natural gas by 2030 or meet equivalent emissions rates through other compliance options. For new natural gas plants operating at a minimum of 40% of their annual maximum capacity, the regulations require 90% carbon capture and storage by 2032.
Operators can achieve emission reductions in a variety of ways, from carbon capture and storage to co-firing natural gas with lower-emitting fuels or improving infrastructure and efficiency. However, the rules do not apply to existing natural gas plants.
Emission rules
To understand the impacts of these varying rules, Luo and Jenkins customized an existing power sector model called GenX. “We added many constraints tailored to the EPA regulations, such as we allow fossil fuel plants to be retrofitted to add carbon capture and storage or to add hydrogen co-firing,” Luo says.
The researchers focused on the coal rules alone, the natural gas rules alone, and the combination of both. They also tested additional, stricter scenarios. They found that almost 70% of the emissions reductions from the rules were due to the coal rules. The mechanism of the emission reduction, the researchers found, is that the rules spur an accelerated timeline for coal plant retirement. Of the 28.3 gigawatts (GW) of operational coal capacity in 2035, 28 GW is expected to be retired by 2039.
The natural gas rules, on the other hand, led to an overall decrease in system efficiency. Because only new plants operating at over 40% capacity must install carbon capture and storage systems, these new natural gas plants will operate below capacity, Luo believes. “That will increase the generation from old natural gas plants,” she says, “so the overall efficiency of natural gas in the system will be lower.”
Subjecting old plants to the same rules as new ones would increase the emissions reductions from the regulations to a decline of 62% in 2040 compared to 2022 levels, the researchers found.
Greenhouse gas emissions
The fate of even the existing rules is in limbo, however. One of the first executive orders issued by President Trump upon taking office directed the administrator of the EPA to investigate the “legality and continuing applicability” of a 2009 ruling that allows the EPA to regulate greenhouse gases under the Clean Air Act. On April 10, the president signed an additional four executive orders designed to boost coal mining and exempt coal plants from regulations around the emission of mercury and other toxic pollutants. Coal currently provides 16% of U.S. electricity generation, while natural gas provides 43%, with renewables making up the rest.
The rules around regulating greenhouse gas emissions can’t be unwound immediately, Luo adds, but the future is uncertain. “I hope that this work can still provide some quantitative support for, if not this regulation, then for the future regulations,” she says.
Luo, Q., and J. D. Jenkins, “US EPA’s Power Plant Rules Reduce CO2 Emissions but Can Achieve More Cost-Efficient and Deeper Reduction by Regulating Existing Gas-Fired Plants,” One Earth, doi: 10.1016/j.oneear.2025.101230 (Mar. 12, 2025).
This article originally appeared in the News Update column in the May 2025 issue of CEP. Members have access online to complete issues, including a vast, searchable archive of back-issues found at www.aiche.org/cep.