Task 29, Task 38 and Task 40 Expert Consultation on the sustainability of bioenergy held in Dubrovnik, 25 – 26 October, 2007, and Task 38 workshop on direct and indirect land use change held in Helsinki 30 March-1 April 2009
Prepared by Annette Cowie, Neil Bird and Susanne Woess-Gallasch
The bioenergy industry is expanding rapidly around the globe in response to climate change and rising oil prices. But serious concerns about sustainability of production, off-site environmental and social impacts, and true greenhouse gas balances need to be addressed.
Some so-called “first generation” biofuel systems, such as ethanol from corn, and biodiesel from canola, deliver minor greenhouse gas mitigation benefits when the direct and indirect emissions associated with crop production, processing, and transport are considered. Other biofuel systems such as oil palm grown in South East Asia for biodiesel have apparently greater greenhouse benefits due to efficient high-yielding production systems. However, when indirect impacts of offsite deforestation and loss of soil carbon, especially in peatlands, are brought into the equation the net effect can be negative compared with fossil fuel systems. In addition, expansion of bioenergy systems, involving direct or indirect land use change, can have negative impacts on other environmental attribute, such as catchment water yield and biodiversity.
Furthermore, some current biofuel systems have negative socio-economic consequences, such as increased food prices and displacement of traditional land uses.
Nonetheless, there are some bioenergy options that are environmentally-friendly, can contribute significantly to mitigation of greenhouse gas emissions, and deliver positive social and economic impacts.
Biofuels based on perennial lignocellulosic (woody) feedstocks generally show more promise, both in terms of net greenhouse benefit and other environmental and socio-economic impacts, than many first generation options based on starch and oilseed crops.
The systems with the greatest benefit are those that utilise residues as feedstock, and employ efficient energy conversion technologies such as combustion for heat or co-generation of heat and power.
There is an urgent need for policy development and operational guidelines to support improved sustainability in the bioenergy industry.
This statement addresses the issue of the timing of greenhouse gas (GHG) emissions and carbon sequestration when biomass from existing managed forests is used for energy to displace fossil fuels. When a stand is harvested and used for energy the carbon that was earlier sequestered during growth is emitted to the atmosphere, and is again sequestered if the stand regrows. In long rotation forestry, carbon is sequestered by the growing stand for many decades before harvest takes place – and after the harvest it may take many decades before the harvested stand reaches its pre-harvest carbon stock.
The difference in timing between emission and sequestration of forest carbon that is observed on a forest stand level has caused some to express concerns about the climate mitigation potential of forest bioenergy. In order to fully understand the climate change effects of bioenergy from existing forests, it is important to consider the entire forest landscape and the wide range of conditions within which forest bioenergy systems operate, long term as well as short term effects and climate objectives, and the interactions between human actions and forest growth. Rather than concentrating on the timing of emissions and sequestration, it is more relevant to focus on assessing the contribution that bioenergy from existing forests may make to the establishment of renewable energy systems that can provide a GHG-friendly energy supply into the future.
Full Paper: Timing Statement Page
Download Paper: On the Timing of Greenhouse Gas Mitigation Benefits of Forest-Based Bioenergy.pdf