Is Biomass Energy Carbon Neutral?

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Felix Grant
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1 Is Biomass Energy Carbon Neutral? By Roger A. Sedjo Resources for the Future 15 th Edition of ICABR Conference on Sustainability and the Bioeconomy Frascati Italy. June

2 Issues: The Role of Bioenergy Two noteworthy letters have been sent to Congress by eminent scientists examining the merits or demerits of biofuels in the climate debate. The first, from 90 scientists (dated May 17th, 2010)] questioned the treatment of all biomass energy as carbon-neutral, arguing that such treatment could undermine legislative emissionreduction goals. The second, by 110 scientists (dated July 20, 2010) expressed concern over equating biogenic carbon emission with fossil fuel emissions, such as contemplated in the EPA Tailoring Rule. Manomet Study Searchinger et al. 2009

3 Carbon neutrality Definition: carbon emissions from the energy source do not increase atmospheric carbon. IPCC early work treated all biomass energy as carbon neutral. Question? Over what period. Time dimension is critical. Undisputed example: If biological material will decompose to carbon dioxide in relatively short time, then if it is converted to energy, would be carbon neutral. Note: The issue is with biomass that would not be decomposing in the relevant time period.

4 Manomet Study Looked at the net emissions profile of harvesting a relatively mature stand and using for biomass energy. Found, not surprizingly, that emissions were large initially and then regrowth gradually resequestered these Thus, if over shorter periods, e.g., 20 years, net emissions would be positive Indeed, net emissions would usually exceed those of fossil fuels over those same periods.

5 Some dimensions Long term vs. Short term Stand specific, forest wide, regulated forest. Manomet Study was short term (to the year 2020) and stand specific (harvested biofuel from a give stand) If biofuels feedstock needs require land use changes, e.g., in Africa, that release carbon, not carbon neutral. (Searchinger et al.)

6 Dimensions (carbon neutral) Suppose long run life cycle (over one rotation) from a stand. Then the harvested wood could be wholly Then the harvested wood could be wholly recovered if no induced land use changes.

7 Dimensions (carbon neutral) Biomass harvested from a regulated steady state forest. So, the amounted harvested and C released in burning into the atmosphere would just equal the amount that the regulated system would sequester in that period. So, no net emissions and it would substitute for the use of fossil fuels for that energy.

8 Dimensions (continued) Could argue: the fossil fuel carbon emission could also be captured in new forest growth. But, note, that would require new growth and not simply replacement growth. So, eventually would run out of new growth opportunities But, could continue biomass energy indefinitely at some prescribe regulated forest (or forest system) level.

9 Carbon neutrality: more complicated version If substitute live biomass for fossil fuel energy, release additional carbon into atmosphere (like fossil fuels) but as the biological system recovers it recaptures the carbon. So, after the biological system has returned to its previous state and energy has been produced. If use fossil fuel instead, need additions to biological system to offset emissions. Since the biological system has limits, this approach involves a cost in lost capacity.

10 Earlier Working Assumptions (IPCC) Biomass energy could be viewed as carbon neutral since emissions would eventually be sequestered in future biological growth. In a steady state biological system (like the classic regulated forest), gross emissions would equal gross sequestration, thus net emissions would be zero. Life Cycle view that Assumes that global biomass stocks return to some long-term steady state, which may not be true.

11 Scientist s Letter and other criticisms note 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 is unlike other renewables, such as wind or solar; that time dimension is essentially ignored. So although net emissions zero over long time periods, often will not be zero in shorter time periods; and that the biomass stock need not necessarily return to the earlier level, e.g., global deforestation. Biomass releases more carbon per energy unit than most fossil fuels.

12 Forest Scientists note: 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, (in the biosphere) as would fossil fuel emissions.

13 The Differences Biomass carbon releases are different from those of fossil fuels in that the Biomass burning process is reversible Carbon can flow back into the biomass so biomass burning need not generally release net additional amounts of carbon into the biosphere over long periods, fossil fuels burning is irreversible. Coal, oil and natural gas which hold carbon captive -- release net permanent additional amounts of carbon to the biosphere.

14 Reversibility Thus the release of fossil fuel emissions is in principle irreversible whereas biomass emissions can be return to biomass. So what? Is this important? Over the long-term it may be. Have to sequester in another sink that may have limited capability

15 Conclusions In the short term emissions, whether from biomass or fossil fuels, accumulate in the atmosphere and contribute to global warming. Biomass energy may not slow down atmospheric carbon build-up in the short run. Also, a life-cycle approach not applicable for a short-term objective like reducing GHG emissions by The long-term implications of fossil fuel emissions for the biosphere are a lasting change in the total carbon balance in the biosphere.

Some Effects of Biogenic Energy on Wood Fiber Markets

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