Benefits occur, but over how many years?

One of the confounding climate-related questions facing the EPA is whether the combustion of biomass for energy exacerbates, mitigates, or has no effect on climate change. 

Attempting to answer the question has proven to be enormously difficult.  Acknowledging the complexity, the Agency issued a rule deferring the application of greenhouse gas (GHG) regulations to biogenic emissions for 3 years until it conducts further research and communications with stakeholders.  But that delaying tactic did not stand up to judicial review, and the EPA was ordered by the U.S. Court of Appeals for the D.C. Circuit to scuttle its deferral rule; in a majority ruling the court found that the Clean Air Act (CAA) did not provide the EPA with the requisite authority to issue a deferral.  The Agency therefore must determine whether sources of biogenic emissions are subject to the CAA’s Prevention of Significant Deterioration (PSD) and Title V permitting regulations for GHGs and, therefore, are required to use the best available control technology (BACT) to reduce those emissions. 

A carbon-neutral designation refers to an energy production activity that essentially generates no net increase in GHG emissions on a life-cycle basis or an activity in which the amount of CO2 emitted during the power production cycle is absorbed by the biosystem.  Life-cycle analyses (LCA) of the biopower pathway include all stages of fuel and feedstock generation or extraction through distribution, delivery, and use of the finished fuel by the ultimate consumer. 

Advocates of the use of biomass to generate power claim that the combustion or decay of biomass (e.g., in municipal solid waste landfills) is carbon-neutral because it is part of the global cycle of biogenic carbon and does not increase the amount of carbon in circulation.  Others assert that carbon released by combusting biomass is no different from carbon released by burning fossil fuel, and that emissions from the combustion of certain biomass, primarily trees, cannot be reabsorbed until forested areas are restored, which can take decades or even centuries.  This results in carbon debt, which refers to the period of excess biogenic emissions and the amount of time it will take to “repay” the debt, that is, reabsorb the emissions.

The carbon-neutral/not carbon-neutral determination for biomass used for energy generation is critical from a regulatory perspective.  Initially, when issuing its 2010 PSD and Title V GHG tailoring rule, the EPA did not exempt emissions from biomass combustion.  But the Agency was aware of the difficulty of conducting an LCA for the biopower pathway.  The challenge was characterized in a report by Kelsi Bracmort, a specialist in agricultural conservation and natural resources policy with the Congressional Research Service (CRS). 

“Whether biopower is carbon neutral depends on many factors, including the definition of carbon neutrality, the feedstock type, the technology used, and the time frame examined,” wrote Bracmort. “Carbon flux (emission and sequestration) varies at each phase of the biopower pathway, given site- and operation-specific factors.”

SAB review

Part of EPA’s research included obtaining a review by the Agency’s Science Advisory Board (SAB) of the “accounting framework” the EPA used for biogenic CO2 emissions from stationary sources in the context of its GHG PSD tailoring rule.  (This action changed the PSD applicability threshold for GHG emissions from stationary sources from 100 and 250 tons per year (tpy] to 75,000 tpy.) 

Through the framework the Agency sought to develop a method for adjusting biogenic carbon emissions from stationary sources to credit those emissions with carbon uptake during sequestration or, alternatively, avoided emissions from natural decay (e.g., from residues and waste materials). Without a way of adjusting those emissions, the Agency’s options would be either a categorical inclusion (treating biogenic feedstocks as equivalent to fossil fuels) or a categorical exclusion (excluding biogenic emissions from determining applicability thresholds for regulation).

Throughout its review, the SAB refers to the challenges the EPA faced in developing the framework as “daunting.”  The SAB acknowledged that the Agency did an “admirable job” of describing the task of quantifying the impact of transforming biologically based carbon from a terrestrial storage pool (such as aboveground biomass) into CO2 via combustion, decomposition, or processing at a stationary source. 

But the framework also has major drawbacks, the SAB found.  Primarily, the EPA did not properly account for various time frames that impact combustion and sequestration.  For example, the Agency sought to determine annual changes in emissions and sequestration rather than assessing the manner in which these changes will impact the climate over longer periods of time. 

The SAB noted that, at the forest stand level, there can be a lag time of up to 100 years between emissions from combustion and sequestration through regrowth.  This length of time may have little effect on the goal expressed in international forums of limiting warming to 2oC by 2050. 

On the other hand, notes the SAB, the large-scale use of forest biomass to displace fossil energy and forest regrowth rates that match harvest rates could leave cumulative emissions unchanged over a 100-year horizon and thereby have minimal effect on the climate. 

The issue is further complicated by the type of biomass used.  For example, while harvesting forests eliminates a source of carbon sequestration, the combustion of logging debris eliminates the release of methane from the debris as it decomposes.  Methane is a much more potent GHG than CO2.  While that may be an advantage for the climate, the current regulatory uncertainty makes it difficult to predict which feedstock type (e.g., trees from forests, logging debris, dedicated energy crops) will be the dominant feedstock for biopower.

How the EPA proceeds on the regulation of emissions from the combustion of biomass for energy will be affected to some extent by stakeholder input.  Here are some carbon-neutral and not-carbon-neutral views stakeholders have expressed.

Carbon-neutral

“The EPA’s deferral rule for biogenic carbon emissions was a sensible response to the situation at the time.  Having the rule vacated does not change the fact that treating biogenic and anthropogenic carbon emissions the same is detrimental to the country’s environmental and economic health.  The recent court case may have altered the timeline for evaluating biogenic emissions, but the end result will inevitably remain the same.  Biogenic emissions from the management of [municipal solid waste] do not introduce new carbon into the existing natural carbon cycle.”
-Solid Waste Association of North America and National Solid Wastes Management Association, letter to EPA, August 2013

“Given recent policy incentives and mandates for renewable energy, concerns over the depletion of forest resources or conversion of forests to other land uses for the production of biomass crops is a significant concern.  However, reversing the long-standing accounting principle of carbon neutrality of biomass is not the correct policy response, particularly given the long-term GHG benefits of biomass energy and the additional health, as well as climate, impacts associated with fossil fuel use.  If policies are put in place that do not recognize the long-term benefits of the biomass carbon cycle, the economic value of keeping land forested will be diminished, and forest carbon sequestration may be reduced as landowners find more economically beneficial uses for their land, such as development.”
-American Forest & Paper Association, comment to Massachusetts Department of Energy Resources, July 2010

“Biogenic GHG emissions will occur through tree mortality and decay whether or not the biomass is used as an energy source.  Some regions of the United States have rampant wildfires contributing pulses of greenhouse gases to the atmosphere.  Capturing the energy value of these materials, thereby offsetting fossil fuel emissions, generates a net effect from burning biomass that is better than carbon-neutral.”
-Letter to Congress from 114 environmental scientists, July 2010

Not carbon-neutral

“The long-term perspective focuses on the much lower amounts of atmospheric carbon that will eventually be realized if biomass is substituted for fossil fuels and the related beneficial effects for climate change and future generations.  From this perspective, the 35-50 year payback period of biomass is less consequential.  The short-term perspective, by contrast, believes near-term emission reductions are critical. This perspective is concerned with near-term ‘tipping points’—climate events that might be triggered by near-term increases in atmospheric carbon. From that perspective, the 35-50 year payback periods for biomass electric power are considered unacceptable climate and energy policy.”
-Southern Environmental Law Center, February 2012

“For the fastest growing biomass crops (e.g., perennial grasses), regrowth can be achieved in a year.  But for other types of biogenic fuel (e.g., whole trees), the debt period may extend for decades or centuries.  When new areas of forest or other vegetation are harvested for fuel, total CO2 emissions can exceed the amount released directly from the facility where the fuel is burned.  One reason is that the soil itself stores carbon, and when trees are cut, soil carbon is released into the atmosphere as CO2.”
-Center for Biological Diversity (CBD), brief, CBD v. EPA, D.C. Court of Appeals, decided July 12, 2013