In the fall of 2010, two noteworthy letters were sent to the Congress by eminent scientists examining the merits – or demerits – of biofuels in the climate debate. The first, from about 90 scientists, questioned the treatment of all biomass energy as carbon neutral, arguing that such treatment could undermine legislative emission-reduction goals. The second letter, by over 100 forest scientists expressed concern over equating biogenic carbon emissions with fossil fuel emissions, what was contemplated in the Environmental Protection Agency (EPA) Tailoring Rule, which provides the guidelines for government carbon accounting. (The letters to Congress are available in the Appendix here.) Such an approach, which focuses on smoke stack emissions, independent of their feedstocks, is feared to encourage further fossil fuel energy production.
The EPA has put off a final decision on guidelines to allow for more research and discussion for two years.
These letters were importantly influenced by the Manomet Study, commissioned by the State of Massachusetts, that argued that the substitution of wood biomass for fossil fuels for producing electrical power would increase emissions of carbon dioxide. Although the issue appears to focus on biomass carbon neutrality – whether carbon emissions from biomass are automatically offset by prior, subsequent, or contemporaneous carbon sequestration in vegetative growth – the issue is more complex. The first letter notes correctly that the “replacement of fossil fuels with bioenergy does not directly stop carbon dioxide emissions from tailpipes or smokestacks.” Thus, biomass energy – fuels derived from wood or other plant material – produces emissions and therefore is unlike other renewables, such as wind or solar. The second letter notes, also correctly, that carbon dioxide released from the combustion of wood biomass is part of the global cycle of biogenic carbon and “does not increase the amount of carbon in circulation,” as would fossil fuel emissions.
These two points are not fundamentally in conflict. Both biomass and fossil fuels store large amounts of carbon. Both release carbon into the biosphere – the biosphere being the whole area of Earth's surface, atmosphere, and sea that is inhabited by living things – upon burning. However, biomass carbon releases are different from those of fossil fuels in that the biomass burning process does not release net additional amounts of carbon into the biosphere. By contrast, burning fossil fuels – coal, oil and natural gas – which hold carbon captive - does release net permanent additional amounts of carbon to the biosphere.
A number of issues emerge. First, if the biomass used would otherwise decompose, then using it for energy creates no new emissions. Second, if the perspective is that of a life cycle (long term) and no indirect land conversion is involved, the eventual replacement of the biomass will also recapture the carbon emitted in energy production. This is the view taken by an earlier Intergovernmental Panel on Climate Change (IPCC) study. Third, if short-term carbon goals are involved, biomass energy could increase short-term atmospheric carbon levels. Indeed, the very nature of a short-term emissions approach does not lend itself to an all-embracing “lifecycle analysis.”
The short-term approach suffers from another deficiency. The approach tends to treat the forest as a fixed stock. Therefore, to us the wood for bioenergy is viewed as reducing the forest stock. However, expectations of the future are known to influence management behavior in anticipation of those future demands. Thus, the establishment of dedicated fuelwood plantations will likely begin before biomass energy demand actually increases, thereby changing the carbon footprint associated with biomass energy. Thus, from a broad forest system perspective, the biomass burning does not release new carbon but simply releases carbon captured and stocked in an earlier period in anticipation of future biomass burning.
Although carbon released by fossil fuels or biofuels has an equivalent impact on the atmosphere, there are important differences. In the case of fossil fuels, the release of carbon results in an irreversible flow of carbon from the fossil fuel stock to the biosphere resulting in a net permanent addition to the total amount in the biosphere. For biomass, by contrast, the amount of carbon in the biosphere has not changed. This lack of equivalence is not without consequence. Only the form has changed as carbon moves over time from being captured in the biomass to being released into the atmosphere, from where it might once again be able to be recaptured in biomass. Thus, the release of fossil fuel emissions is, in principle, completely irreversible whereas biomass emissions are reversible and can be returned to biomass.
In conclusion, biomass carbon is a zero sum game – in the long run. Over shorter periods of time and for individual sites, however, the question is more complex. More broadly, global warming is a long-term challenge to humanity. The contest is a marathon, not a sprint. Having the lowest carbon emissions for energy production to the year - say 2020- in itself, may not address the fundamental problem of reducing emissions, which will persist into the next century and perhaps beyond. There is no silver bullet solution to climate change. We need all the tools we can bring to bear. An important role can be played by forests and biomass energy, which, if correctly utilized, can contribute significantly to reducing net carbon emissions and do much to assist in addressing the fundamental problem.
For more on biomass energy, read Carbon Neutrality and Bioenergy : A Zero-Sum Game?
