Technical Note BB18: Bioenergy is carbon neutral
IPCC Guidelines consider biomass used for energy to be carbon neutral if from organic waste and plantation forests.
Biomass used for energy can arise from liquid or solid organic waste streams; forest residues after extraction of logs; crop residues after harvest; or purpose-grown energy crops.
A natural forest remains carbon neutral over millennium with trees dying and new ones growing to replace them as well as the soil carbon recycling and remaining at constant levels. The exception is loss of biomass (and hence reduction in carbon stock) from degradation by external influences such as deer or possum browsing. While the use of biomass sourced from organic waste and plantation forestry are considered to be carbon neutral the Intergovernmental Panel on Climate Change (IPCC) Guidelines do not automatically consider biomass used for energy as "carbon neutral," even if the
biomass is thought to be produced sustainably, because:
- in any time period there may be CO2 emissions and removals from the atmosphere due to the harvesting and regrowth of bioenergy crops;
- land use changes (including soil carbon content fluctuations) caused by biomass production can also result in significant GHG fluxes; and
- there may also be significant additional emissions which are estimated and reported in the sectors where they occur e.g.:
- from the processing and transportation etc. of the biomass when fossil fuels are consumed;
- direct methane and nitrous oxide emissions from the biomass combustion;
- from the production and use of fertilisers and lime if either is used in cultivation of the biomass.