The Biomass Carbon Debate: When To Start Counting?

RenewableEnergyWorld.com
October 20, 2011
By John S. Gunn, Manomet Center for Conservation Sciences

Manomet says the goal of its study was to assess the immediate carbon impact of switching from fossil fuels to woody biomass.

New Hampshire, U.S.A. -- In June 2010, the Manomet Center for Conservation Sciences released the results of a study on burning woody biomass for energy in Massachusetts.

Since then, several critiques have appeared, including one recently published in the July/August 2011 issue of Renewable Energy World North America by William Strauss.

The Commonwealth of Massachusetts asked Manomet and our partners to quantify the impacts — positive and negative — on greenhouse gas emissions and forest health if Massachusetts switched some proportion of energy production from fossil fuels to wood. For greenhouse gas (GHG) emissions, the policy-relevant question was: What will the atmosphere "see" if Massachusetts switched from fossil fuels to biomass energy? The timing of the emissions mattered because Massachusetts had set a goal of reducing greenhouse gas emissions by 10-20 percent from 1990 levels by 2020 and 90 percent by 2050. The state wanted to promote renewable energy technologies that could help meet that time-specific goal.

The study found that, initially, switching to the combustion of forest biomass to generate electricity or heat would produce more GHG emissions than burning fossil fuels to generate the same amount of energy. This is due to the low embedded energy of wood relative to fossil fuels - for the energy technologies we evaluated, wood releases more GHGs per unit of usable energy. However, as forests grow back, this carbon "debt" is reduced and eventually replaced with a carbon "dividend" (relative to fossil fuels). The length of time to pay off the debt can vary from a decade to a century, depending on an array of factors outlined in our study.

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