Science Panel Completes Review of EPA CO2 Accounting Framework for Bioenergy

The panel acknowledged the tremendous complexity of accounting for CO2 emissions from the wide variety of types of biomass feedstocks and bioenergy systems. However, it also found many aspects of the EPA’s proposed Framework that could be strengthened and improved from a scientific standpoint.

On September 28, the EPA Science Advisory Board (SAB) transmitted its final report, " SAB Review of EPA’s Accounting Framework for Biogenic CO2 Emissions from Stationary Sources ," to the EPA Administrator. This concluded a year-long review by a multi-disciplinary panel of scientists of the EPA’s proposed " Accounting Framework for Biogenic CO2 Emissions from Stationary Sources " . The review process included several opportunities for public discussion by the panel and public comment on the EPA’s proposed Framework, as well as on successive drafts of the SAB biogenic panel’s report. The proposed Framework and scientific review stemmed from a July 2011 EPA announcement, " Deferral for CO2 Emissions from Bioenergy and Other Biogenic Sources under the Prevention of Significant Deterioration (PSD) and Title V Programs " (76 FR 15249), in which the EPA said it would delay regulation of major biogenic stationary sources of CO2 emissions for three years so that it could review the associated scientific and technical issues.

As background, the panel begins by observing: " Biogenic CO2 emissions from bioenergy are generated during the combustion or decomposition of biologically-based material. Biogenic feedstocks differ from fossil fuels in that they may be replenished in a continuous cycle of planting, harvesting and regrowth. The same plants that provide combustible feedstocks for electricity generation also sequester carbon from the atmosphere. Plants convert raw materials present in the ecosystem such as carbon from the atmosphere and inorganic minerals and compounds from the soil (including nitrogen, potassium, and iron) and make these elemental nutrients available to other life forms. Carbon is returned to the atmosphere by plants and animals through decomposition and respiration and by industrial processes, including combustion. Biogenic CO2 is emitted from stationary sources through a variety of energy-related and industrial processes. Thus, the use of biogenic feedstocks results in both carbon emissions and carbon sequestration. "

The question before the EPA and the SAB biogenic panel is how best to account for the changes in carbon stocks and flows that may result from the production and use of biomass for industrial and energy production.

The panel agreed with the EPA that not all biogenic emissions are a priori carbon neutral; biogenic emissions from stationary sources should be neither categorically excluded from regulation nor categorically included (i.e. regulated in the same way as stationary sources that use fossil fuels). Different types of biomass feedstocks and biogenic stationary sources can have varying impacts on carbon stocks and flows between living plants, decaying organic matter, soils, and the atmosphere over time. Some systems may result in net zero CO2 (or even net carbon negative) emissions, while others may result in substantial net carbon positive emissions in the short term. In the panel’s view, biogenic stationary emissions sources and their biomass feedstocks should be assessed based on a default "biogenic accounting factor" (BAF) that the EPA would calculate for a number of general categories of feedstocks, which "might vary by region, prior land use, and current land management practices."

The EPA Framework, as proposed, would calculate a BAF for each stationary source based on a number of factors relating to carbon emissions and storage from the biomass production and consumption systems. The BAF would range from zero (i.e. zero net CO2 emissions during the course of a year) to one (i.e. similar to emissions from fossil fuels with zero off-setting carbon sequestration).

The panel concluded that the Framework was best suited in its current form for accounting for net CO2 emissions from biomass resources with shorter carbon life cycles, such as agricultural residues from annual crops and biomass from short rotation perennial energy crops. The Framework needs much more refinement for other types of biomass that have more complicated and long term carbon life cycles or rates of decay. For example, although many biogenic sources may use biomass that otherwise would simply decay and emit CO2 (so-called "anyway" emissions), the release of CO2 from decaying biomass is not always instantaneous, as it is when the biomass is combusted in a biomass plant. Woody biomass residues might lie on the forest floor or in landfills decomposing for many years. They also might be burned immediately in open fires or consumed by wildfires. The panel recommends that the EPA refine its model to account for the varying timescales and alternative dispositions of different types of biomass from waste and residue streams.

Of greatest concern to the panel are the temporal and spatial scales used by the EPA Framework. The panel wonders why the EPA is using an annual timeframe, analyzing net changes to carbon stocks and flows within seemingly arbitrarily established regions, and using a fixed reference point for each region as the basis for evaluating net carbon changes over time. What is the scientific basis for these choices? The panel observed that: 1) depending on the type of biomass that is used, the timescale of a biomass facility’s impact on carbon stocks and flows across its landscape may span decades, not just a single year; 2) the spatial scale of analysis should be related to the actual landscape and working lands across which biomass is being produced and consumed and a biomass facility is operating; and 3) net changes in carbon stocks and flows for any given biomass facility within its landscape over time should be compared to models estimating the "anticipated baseline" for changes in carbon stocks and flows over the same period without the biomass facility – not a static reference point.

By using a one-year accounting timeframe, the EPA is ignoring the fact that some types of biomass (e.g., whole trees) can take several decades to complete a full carbon cycle from harvest to full re-growth, and that, in the interim period of some decades, a significant amount of CO2 may be shifted from sequestration in living trees and soils to the atmosphere where it may affect the climate. The potential for a pulse of CO2 emissions into the atmosphere from a rapid increase in the use of whole trees for bioenergy could create significant global warming potential if it is not balanced by an equal or greater amount of simultaneous CO2 sequestration elsewhere. While the panel acknowledges that, over the long term, sustainably produced forest biomass could be beneficial for climate stability (when it off-sets the use of fossil fuels), the panel is concerned that the Framework does not capture this potential short term effect.

The panel believes the reference point method and one year timeframe used in the Framework to account for changes to CO2 stocks and flows likely will not capture the full impacts of a biogenic facility that harvests whole trees. The panel acknowledges the significant uncertainties and methodological challenges of rigorously and accurately modeling future forest growth scenarios. However, the panel nonetheless recommends developing a business-as-usual (BAU), anticipated baseline model for the fuel shed. " In general the Framework should provide a means to estimate the effect of stationary source biogenic feedstock demand, on the atmosphere, over time, comparing a scenario with the use of biogenic feedstocks to a counterfactual scenario without the use of biogenic feedstocks. "

The panel notes that the choice of the time scale for assessment is essentially a policy choice, not a scientific one, but the panel believes that policymakers need to be informed of the possible implications for the climate in both the short term (e.g. 20 years) and the longer term (e.g. 100 years). At the same time, the panel acknowledges that the science is not settled on whether a pulse of biogenic emissions in the short term will have much, if any, impact on the climate system over the next hundred years or more, if the emissions from the renewable biomass that is harvested are fully off-set by carbon sequestration in plants and soils, and if fossil fuels are actually displaced.

With regard to "leakage" and indirect land use change due to biomass production, the panel observes " We do not recommend incorporating a measure of leakage in the estimate of BAF which would effectively hold a stationary facility responsible for emissions that are outside its control and occurring due to market effects. There is no literature in the social sciences to show that this is an effective way to control emissions. " However, the panel nonetheless urges the EPA to establish estimates of at least the directionality (+/-), if not the magnitude, of any leakage. This would help inform policymakers as to whether further policy steps may need to be taken separately to address it.

The panel also recommends expanding the Framework to include other greenhouse gases (GHG) associated with bioenergy production. For example, N2O may be emitted when nitrogen fertilizer is used to grow biomass, or CH4 emissions may be avoided by the diversion of organic matter away from landfills to bioenergy production. Both of these GHGs have much higher global warming potential than CO2, ton for ton, and thus, they should be factored into any life cycle analysis of the climate impacts of different biomass and bioenergy production systems.

The panel urges the EPA to more carefully quantify and incorporate the impacts of various types of biomass production in different regions on soil carbon stocks and flows over time across both agricultural and forestry sectors. Anticipated baselines should be established for comparison.

" The Framework should clarify how a negative BAF would be used and whether it could be used by a facility to offset fossil fuel emissions. Restricting BAF to be non-negative would reduce incentives to use feedstocks with a large sequestration potential. "

Finally, the SAB panel questioned the efficacy of regulating CO2 emissions from biogenic sources under provisions of the Clean Air Act. The panel observed that there are far more effective and efficient policy mechanisms for reducing GHG emissions than the very limited scope and mechanisms of the Clean Air Act - such as a comprehensive cap and trade policy or a carbon tax policy. However, since the EPA is pursuing this path, the panel says it is essential that the EPA apply the same criteria and scope of analysis to major emitters that use fossil fuel as it does to biogenic sources (e.g. conducting full life cycle analysis instead of just measuring smokestack emissions). This is to assure that the implementation of any future regulation of biogenic sources under the Clean Air Act will be equally objective and scientifically rigorous for all major emitters.