Wood pellets have been hailed as a carbon neutral form of energy. As a result, the wood pellet market has been rapidly growing, especially in Europe, where wood pellets are being used to satisfy Paris Agreement requirements to reduce carbon emissions. However, pellet production can result in additional harvests of biomass and therefore minimize the amount of carbon stored in forests. To determine the extent of the overall carbon stock loss or gain from wood pellets, carbon life cycle assessments (CLCA), which include everything from pellet production to transportation to waste disposal for each bioenergy project are needed.
The southeastern US forests produce the bulk of wood pellets burnt for electricity production in the UK, but the impact of producing these pellets on the carbon stocks of the surrounding forests is unknown. In order to improve forest management, mitigate climate change, and develop good environmental protection legislation, the Southern Environmental Law Center (SELC) and the National Wildlife Federation (NWF) were interested in doing a CLCA on some of these pellets.
To help them with this, SIG collaborated with the Pinchot Institute for Conservation to analyze the origin of stocks for select pellet mills in Louisiana and Mississippi, as well as model carbon dynamics to the point of combustion. The first step for this project was to do a forest owner survey, which found that most of the stock for the pellets comes from non-industrial private forest (NIPF) softwood plantations, which would not be thinned if a pellet market did not exist. SIGs model then estimated the carbon stored in wood products, as well as impacts to the forest carbon stocks with and without thinnings.
Results (found here and here) from this study found that over the course of the 40 future years modeled, carbon parity was not achieved for pellet mills compared to the fossil fueled portions of the UK electricity grid. This means that, even over 40 years, wood pellets produced higher emissions than other likely or traditional energy sources, such as coal or other fossil fuels. This result also holds up when mixing NIPF softwood plantation feedstock with a large share (>40% of total) of a low-emission feedstock, such as sawmill residues.
While these results showed that the production and use of pellets in this situation were not climate beneficial, it is important to keep in mind that each bioenergy CLCA is different. There are bioenergy projects that can be beneficial to the climate (e.g. heat and electricity generation instead of pile burning), particularly in the western US, but there are also some that are not. While some basic metrics frequently drive outcomes (e.g. does the project involve additional harvests that would not have otherwise occurred, is biomass being diverted from supply chains for other long-lived products, is only electricity produced along with usable heat to offset fossil fuel use?), in-depth and case-by-case analysis is important for assessing the climate impact of a given bioenergy project.