IEA Bioenergy: Dispelling misconceptions on climate effects of bioenergy from managed forests
Articles in the media have raised concerns over the climate effects of bioenergy from managed forests. Some statements seem to reflect misconceptions about forest bioenergy, so scientists within IEA Bioenergy have prepared a document presenting key facts about the use of forest biomass for climate change mitigation.
Wood harvested from forests is typically used to produce a range of products such as sawnwood and wood panels. It is the residues from forestry operations (tops, branches, thinnings, damaged stems) and wood processing that are typically used for bioenergy. Well-managed forests store carbon while also producing wood and energy products that can be used in place of carbon-intensive building materials and fossil fuels.
Burning biomass for energy emits carbon dioxide that is part of the continuous exchange of carbon between plants and the atmosphere. In contrast, fossil fuel emissions represent a one-way flow of carbon from geological storage, deep underground, into the atmosphere. Therefore, the effect on atmospheric GHG concentrations of switching from fossil fuels to biomass cannot be determined by comparing CO2 emissions at the point of combustion.
Because it is part of the short-term carbon cycle forest bioenergy is often said to be “carbon neutral”, but this should not be assumed. Greenhouse gas (GHG) emissions in the supply chain (e.g., from fuel used in harvest, processing and transport) and impacts on forest carbon stock must be taken into consideration. To determine the climate effects of using forest biomass for energy, we need to compare with the GHG emissions in a scenario where other energy sources are used. Such life cycle comparisons show that forest-based bioenergy can deliver substantial emissions reduction. Even long-distance transport does not negate the climate benefits of woody biomass as a renewable energy source when derived from sustainably managed forests.
The concept of “carbon pay-back time” is sometimes referred to when forest bioenergy is debated. Sometimes payback times are calculated using an overly simplistic approach that considers a single harvesting event and neglects to consider how forest management affects forest carbon balances across the larger forest landscape. In other cases, it is assumed that commercial forest managers will stop harvesting their forests altogether if there is no demand for bioenergy.
A key requirement to ensure climate benefits is that forests are regenerated and the long-term capacity of the forest to absorb carbon from the atmosphere is maintained.
It is critical to focus on the global emissions trajectory required to achieve climate stabilization. The most important climate change mitigation measure is the transformation of energy, industry and transport systems as soon as possible, so that fossil carbon remains in the ground. Bioenergy plays a strategic role in supporting this transformation.