In the long term, a sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual sustained yield of timber, fiber, or energy from the forest, will generate the largest sustained mitigation benefit." –IPCC
Despite global support for the IPCC's view that sustainably managed forests play a critical role in climate mitigation, pockets of disagreement have gained traction in the US (read a related post:Dividend then Benefit). A recent comprehensive review of research on the life cycle carbon accounting for wood, which was recently published in the journal Carbon Management, is the most important piece of scholarship to support the IPCC's view. It is also the most important piece of scholarship to date undermining arguments like those made in the Manomet study that wood as an energy source has higher emissions than coal.
This new study, conducted by Lippke et al,* reviews recent research on life cycle carbon accounting across all stages of processing, from cradle-to-grave. While the study is much more comprehensive than I can do justice to here, a few of the conclusions should be an essential part of the knowledge base of all wood bio-electricity facilities facing opposition.
Peer reviewed primary life cycle data allowed the authors of the study to complete GHG emission comparisons for different power plants. They found that "each mega joule of electricity that a woody biomass plant produces generates only 4% of the emissions from a bituminous coal plant, using a fossil fuel base for comparison. This is in direct contrast to the proposed EPA method where the CO2 uptake in the wood from the atmosphere is treated the same as if it were mined like coal rather than sourced from sustainably managed forests." Even using the EPA's proposed method, the group found, a biomass plant's emissions would equal just 86% of the emissions from a coal plant.
The study's authors found that, by using life cycle carbon accounting, they could expose the unintended consequences of current policies designed to reduce or mitigate carbon emissions. Policies based on only one carbon pool, it turns out, can do more harm than good. One of the most serious negative impacts has been created by carbon exchanges, which offer incentives for reducing harvests in order to increase carbon stores. By ensuring the use of more fossil fuels (coal instead of biomass), however, these policies actually lead to higher carbon emissions.
Fossil fuel emissions are by far the largest contributor of carbon emissions to the atmosphere. The study concludes that displacing fossil fuels with wood from sustainably managed forests will provide the maximum rate of carbon absorption possible.
"While maximizing forest growth contributes more wood to utilize, the dominant source of carbon mitigation comes from sustainably displacing fossil emissions through the use of wood since the carbon stored in the forest is a one-time creation and can only contribute to sustainably reducing carbon emissions by harvesting the wood to substitute for other materials."
In essence, the amount of carbon that trees sequester drops as the trees age; they then die and decompose. At this time, the benefit of not harvesting the trees has been completely obliterated. From a life cycle impact perspective, harvesting trees when they can provide the most carbon benefits, including long-lived wood products (lumber, engineered wood products, trusses, etc.) that can be substituted for other building materials (steel, concrete) and energy products (biomass, in-woods chips, etc.) that can displace fossil fuels, is best carbon mitigation strategy available.