Carbon neutral biomass energy?

Done right, biomass can be part of a sustainable energy future. Done wrong, it will add to already dangerous levels of CO₂. As a recent article in the New York Times points out, considering biomass energy to be carbon neutral could hinder the US from achieving its climate goals. As wood is less energy dense than coal, burning wood emits about 50% more CO₂ than coal to produce the same amount of energy.[1] Forests can reabsorb these carbon emissions, but it will take many decades or even centuries for the forest to grow back.[2] There needs to be a guarantee that the land will remain in forest use for at least as long as it takes to reabsorb the initial carbon emissions.

The following questions can help determine whether a biomass project is carbon neutral:

1. Is the wood being used waste material? Biomass energy can make sense if the wood comes from restoration waste materials or mill residue. Unfortunately, only about a quarter of woody biomass used for energy in California in 2012 came from waste products.[3]

2. What is the source of the wood? Is this part of a restoration harvest for otherwise non-sellable wood that will create a forest with older trees, diverse structure, and resilient carbon stores? In this case, biomass could be a part of a sustainable system that maintains or increases forest carbon stores while providing habitat for wildlife and other benefits.

3. Will the land remain forested? Recognizing that it can take decades or more for the forest to reabsorb the carbon emitted, the land needs to be protected for the long-term, such as through conservation easements or other equally effective means.

4. Is the biomass plant efficient and clean? The more efficient the biomass plant can be at converting wood into energy, the greater the potential benefits from biomass. Combined heat and power biomass plants are even better. New technology can also help reduce the health impacts of biomass plants.

There is a role for clean, green biomass energy as a renewable and sustainable fuel source in the 21^st century. How long it takes for the atmosphere to see a net carbon benefit when compared to fossil fuels depends on what material is being used to produce the biomass and the age of the trees. [4] To be truly sustainable, woody biomass should come from protected forests that are managed for long-term resilient conditions. If done well, newer small-scale biomass plants can be a dependable source of renewable energy at a scale that complements responsible forest management.

[1] Hagen, John. 2012. Biomass: Recalibrated. Manomet, Winter 2012. Available at: http://magazine.manomet.org/winter2012/biomass.html

[2] Mitchell, S. R., Harmon, M. E. and O’Connell, K. E. B. (2012), Carbon debt and carbon sequestration parity in forest bioenergy production. Glob. Change Biol. Bioenergy, 4: 818–827. doi:10.1111/j.1757-1707.2012.01173.x

[3] McIver, Chelsea P.; Meek, Joshua P.; Scudder, Micah G.; Sorenson, Colin B.; Morgan, Todd A.; Christensen, Glenn A. 2015. California’s forest products industry and timber harvest, 2012. Gen. Tech. Rep. PNW-GTR-908. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 49 p.

[4] Hagen, John. 2012. Biomass: Recalibrated. Manomet, Winter 2012. Available at:  http://magazine.manomet.org/winter2012/biomass.html