New Air Pollution Rules Could Reduce US Electric-Sector CO2 Emissions By More Than 4 Percent

December 23, 2011 | Alex Trembath, Jesse Jenkins,

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Updated: This post was originally published on January 1, 2012. It was updated on January 27, 2012 to reflect the announced closure of six coal-fired power plants in Ohio, Pennsylvania, and Maryland.

Two new federal air pollution regulations are expected to spur the closure of up to 69 aging, inefficient, coal-fired power plants, reducing both harmful air pollutants and emissions of the climate destabilizing greenhouse gas, carbon dioxide (CO2), according to an AP survey of US power plant operators and a preliminary Breakthrough Institute analysis of the likely impacts on CO2 emissions.

According to the AP survey, 31 coal-fired electricity generating units at power plants in a dozen states are expected to close rather than face costly upgrades to comply with a pair of new EPA regulations designed to curb emissions of smog-forming pollutants and toxic smoke stack emissions. These plants are joined by four plants in Ohio that were formerly classified by the AP survey as "at risk for closure" and two plants in Pennsylvania and Maryland that were not on AP's list. These units have a combined nameplate capacity of 15,532 megawatts.*

Up to 32 additional coal-fired units with a combined 9,714 megawatts of capacity may also decide to close, as the costs of compliance with the EPA's recently enacted Cross-State Air Pollution Rule, designed to curb air pollution in states downwind from coal-fired power stations, and the new Mercury and Air Toxics Rule announced this week both take effect.

While the purpose of these regulations is to reduce harmful pollutants and improve public health, closure of these aging plants will also lead to a 1.4 to 4.4 percent reduction in US electric power sector emissions of carbon dioxide (CO2), according to an analysis completed by the Breakthrough Institute. These air pollution regulations are thus a prime example of the ongoing success of pragmatic, "oblique" strategies to reduce greenhouse gas emissions.



We estimate that the 37 coal-fired generating units most likely to close in response to the new pollution regulations are responsible for almost 54 million metric tons of CO2 emissions annually, or 2.4 percent of US power sector CO2 emissions in 2010 and 1.0 percent of all US CO2 emissions (see tables below for details). Total CO2 reductions could reach 99.3 million metric tons if the additional 32 coal units at risk of closure also decide to retire.

If these shuttered, fossil-fueled generating units are replaced by zero-emissions renewable or nuclear power plants, total US power sector CO2 emissions would fall by up to 4.4 percent from 2010 levels (equivalent to a 1.8 percent reduction in total 2010 US CO2 emissions).

The net reduction in CO2 emissions would be reduced if closing coal-fired plants are replaced instead by generation from natural gas power plants, which are expected to significantly increase their share of US electricity generation in the coming years. Electricity generated by a natural gas combined-cycle power plant emits less than half the carbon dioxide as a typical coal-fired power plant. As such, we estimate that replacing all the retiring generation with electricity from gas-fired plants would reduce US power sector emissions between 1.4 and 2.6 percent, relative to 2010 levels, depending on the number of power plant closures. That would be the equivalent of a 0.6 to 1.0 percent reduction in total US CO2.

The new federal air pollution regulations are thus likely to indirectly result in modest but noticeable reductions in CO2 emissions, with the precise impact depending on the number of power plant closures and the replacement electricity sources.

As we argue along with our Hartwell Group colleagues in the July 2011 report, "Climate Pragmatism," these "oblique" pollution control measures can work to reduce both conventional pollutants and greenhouse gas emissions without relying on climate mitigation as the central justification.

The enforcement of this pair of new EPA air pollution rules is thus one small, successful example of the kind of "no regrets" pollution reduction policies that can achieve near-term reductions in carbon emissions.



37 coal-fired generating units are slated for closure as a result of the new EPA rules:




32 more coal-fired generating units are at risk of being shuttered due high mercury content:



*2006 emissions figures. Data: All other data from Sierra Club Beyond Coal database.
**When AP and EIA data on capacity differed, we used EIA figures.

*Note: two additional gas-fired generating units with a total capacity of 129 MW also made the AP's list of likely closures (Fox Lake in MN and Anadarko in OK). These plants are excluded from this analysis however.

Note on methodology: these calculations are preliminary estimates based on available data for power plant CO2 emissions drawn from a variety of available sources. CO2 emissions data are available only at the power plant level. If a power plant has multiple generating units, we apportion CO2 emissions to the specific generating units expected to close based on their share of the power plant's total nameplate capacity. As different generating units operate at both different efficiencies and for differing amounts of time each year, this methodology may either somewhat under- or over-estimate the CO2 emissions associated with a given generating unit. More precise results would require obtaining data on heat-rates and capacity factors or annual generation for specific generating units at each multi-unit power plant. (Please contact if you have access to additional data that could be used to refine this analysis.)