Climate effects of wood used for bioenergy

13-08-2013 | Publication

Using logged trees as a bioenergy source – replacing fossil fuel – carries the risk of first increasing CO2 emissions before reducing them. It could in fact take up to 100 years before emissions begin to decrease. Using crop residues or wood waste does not have this downside, or to a lesser extent. If felling were to increase to provide more energy through biomass, this could hinder rather than help achieving the CO2 targets for 2020 and 2050.

Sustainability criteria to prevent an increase in CO2 emissions

Ambitious policy goals for renewable energy and greenhouse gas reduction may lead to increased demand for wood from other sources, such as forest residues or even whole trees. Currently, the European Commission is preparing sustainability criteria for solid biomass. These criteria will be crucial to prevent a situation where climate policy that is aimed to reduce CO2 emissions by 2020, 2030 or 2050 actually leads to an increase in emissions.

Wood waste better than logged trees for bio energy

The felling of trees and thinning of forests often leaves wood residues behind in the forest, which slowly disintegrate. In the short term, combusting these residues will lead to more CO2 in the atmosphere and it may take several years – in some cases decades – before any real CO2 reductions are achieved.

The vast majority of forests is relatively young. If trees are not felled, they are able to grow further and absorb large amounts of CO2. Newly planted trees do not grow as fast in the first years of their lives. It therefore not only takes time to regrow them, but also to compensate for the temporary reduction in CO2 absorption. In many cases, it will take more than 100 years before an actual reduction in CO2 in the atmosphere is achieved, compared to a situation in which fossil fuels are used. For the carbon balance it, therefore, remains preferable to use felled trees first as building material or in consumer goods, postponing their use as a bioenergy source until the very end of their life span. In this way the absorbed carbon remains stored within the wood for as long as possible. However, this does mean that wood is not immediately available as an energy source.

This study by PBL Netherlands Environmental Assessment Agency was performed at the request of the Ministry of Infrastructure and the Environment. The project has been supported by Alterra Wageningen UR, commissioned by NL Agency.