A recent commentary I wrote emphasized the need to “do the math” to figure out if switching energy pathways from fossil to woody biomass will have the climate benefits that many assume it will. I have been working on this issue since the 2010 Manomet study that addressed this question for proposed stand-alone biomass electric plants in the state of Massachusetts. Through that study, and subsequent work, we have learned three key lessons when it comes to the question of emissions generated by switching from fossil fuels to wood: 1) it matters what kind of energy is being produced (and what kind of fossil fuel is being replaced, if at all); 2) where the energy feedstocks come from matters (e.g., tops and limbs from harvests already happening, or new harvests of whole trees); and, 3) how we manage the forest (at both the stand and landscape scales) will influence whether emissions benefits will accrue in the short term, long term, or not at all.
The new paper I co-authored with colleagues from the Spatial Informatics Group – Natural Assets Laboratory (SIG-NAL) in the journal Energy explores these first two points when the heating source of homes in New England is switched from fossil fuels such as heating oil and propane to wood pellets derived from local mills. This work was conducted at the request of the Northern Forest Center, a Concord, New Hampshire based NGO that promotes wood pellet heat as an economic development tool that reduces heating costs, supports local forest sector jobs, and reduces dependence on fossil fuels. The Northern Forest Center wanted to know if they can feel confident about the atmospheric benefits of using wood pellets for heat in the region. Our conclusions support that notion.
Here are the key findings from the research:
- Pellets from sawmill residues showed strongest GHG benefits compared to fossil fuel.
- Making pellets from up to 75% pulpwood and 25% sawmill residue produced benefits.
- Shifting existing harvest of pulpwood volume to pellets is climate beneficial.
- Market scenarios decreasing or increasing harvest levels greatly affected results.
Net GHG emissions across a representative wood supply area in the northeastern US by carbon accounting category and timescale with example feedstock mixes for each economic scenario. All scenarios assume that 50% of the feedstock is derived from sawmill residues while the remaining 50% are sourced from forest operations. Pellets from new harvests in addition to current harvest activities (a) as well as pellets derived from harvests that would have not been executed due to the closing of pulp mills (c) result in a net GHG increase mostly driven by net GHG emissions occurring in forest carbon pools (green). Pellets derived from harvests that would have occurred anyway to supply (now closed) pulp mills (b) result in a net GHG decrease mostly driven by reduced avoided fossil fuel emissions from both pulp manufacturing and fossil-fuel based heat.