In a report, EPA’s Science Advisory Board (SAB) has identified “uncertainties, technical difficulties, data deficiencies, and implementation challenges” in the Agency’s September 2011 Accounting Framework for Biogenic CO2 Emissions from Stationary Sources.

The intent of the framework is to initiate development of an approach to account for CO2 emissions from stationary sources that combust biological material such as agricultural and forest products. The need for the framework arose in the context of EPA’s prevention of significant deterioration (PSD)/Title V permitting requirements for certain large facilities that emit or increase their CO2-equivalent emissions by specific amounts, or thresholds. In conjunction with the PSD greenhouse gas (GHG) threshold rule, the EPA announced that it would defer permitting requirements for biogenic stationary sources for 3 years while committing to a detailed examination of the issues associated with biogenic CO2.

Carbon stocks

The essential issue addressed in the framework is how to adjust stack emissions from bioenergy facilities based on the changes in carbon stocks in soil, plants, and forests. Combustion of biomass is considered by many a desirable form of renewable energy use. CO2 is also sequestered in biomass, and biogenic CO2 emissions from stationary sources are emitted during the storage, processing, and consumption of biologically based feedstocks. There are also questions about whether the use of biological material can, in fact, result in increased sequestration over time. These and related issues result in the need for a scientifically based CO2 accounting system.

In general, EPA's accounting framework is intended to be broadly applicable to situations in which there is a need to represent the changes in carbon stocks that occur off-site, beyond the stationary source, or in other words, to develop a "biogenic accounting factor" (BAF) for biogenic CO2 emissions from stationary sources. The Agency subsequently asked the SAB to comment on specific aspects of the framework, such as how accurately it represents changes in carbon stocks that occur off-site, the scientific rigor of the framework, and whether it is simple to implement and understand.

While recognizing that the framework is a step forward in considering biogenic carbon emissions, the SAB found that the framework was particularly deficient in accounting for the carbon outcome of forest-derived wood biomass. EPA’s approach here is regional, wherein a facility’s BAF would be zero if usage occurs in a region where carbon stocks are increasing. The SAB’s approach instead recommends what it calls a “baseline” approach that requires selecting a time period and determining what would have happened anyway without the harvesting and comparing that impact with the carbon trajectory associated with harvesting biomass for bioenergy.

The SAB found that the framework captured many of the factors necessary for estimating the off-site carbon change associated with the use of faster-growing biomass, particularly agricultural products. However, the SAB also believes that the baseline approach is still necessary to reflect changes in landscape and other dynamic processes.

The SAB also noted that the framework should do more to address leakage–the phenomenon by which efforts to reduce emissions in one place affect market prices that shift emissions to another location or sector. In addition, the SAB found that the framework lacked crucial implementation details.

The SAB’s report on the EPA framework is at http://yosemite.epa.gov/sab/sabproduct.nsf/WebBOARD/3EBF802521ACB19585257A470047F1EE/$File/7-26-12+Biogenic+Carbon+Advisory.pdf. The framework is at http://www.epa.gov/climatechange/Downloads/ghgemissions/Biogenic-CO2-Accounting-Framework-Report-Sept-2011.pdf.