Understanding Greenhouse Gas Balances of Bioenergy Systems

摘要: Bioenergy systems play a key role in the UK’s energy future because they offer triple benefits of being renewable, sustainable and incurring lower greenhouse gas (GHG) emissions than fossil fuels, such as coal, oil or gas. When biomass is utilized an source, carbon dioxide (CO2) that was recently captured from atmosphere by plant growth re-released. As this has been sequestered, it often ignored not contributing to net increases long term atmospheric concentrations. However, neutrality dependent on vegetation recapturing equivalent over short time horizon, otherwise balance between biosphere shifted. In natural world, every unit emitted impact needs be considered and, given tight budget constraints faced UK, must assessment. expected deliver 8-11% primary demand 2020 around 12% 2050 (DECC 2012), playing delivering policy commitments reductions. See section 1 – Why bioenergy important UK mix? achieve GHG reductions displacing relatively high intensity existing fuel with feedstock incurred along its supply chain (usually fuel) incumbent. Verifying therefore requires consideration whole awareness wider impacts implementation. Techniques life cycle assessment (LCA) can used verify this. done yield usable material produced nearly always important; fertilizer use for annual crops; changes stocks may very significant forestry land-use change have large perennial crops. A summary which issues tend most crops why 2 What are differences different systems? Every system their balances independently verified. Nevertheless, there many examples bioelectricity achieving substantial savings, while low dominant heating sector, making more difficult achieve. Biomass-derived liquid transport fuels technologies potential savings reported do result savings. Section 3 Can “real” reductions? shows real achieved, but certain factors, including reference comparison substantially alter calculated 4 How reports reach conclusions about examines classifies main drivers variation LCA systems. Some “real”, where actually give rise physical levels emissions. Other sources methodological thought using answer “different question” same system. It absolutely critical “LCA asked clearly adequately defined. 5 –What should when assessing if gives guidance formulating questions what makers defining reduction objectives e.g. consider displaced, whose perspective “reductions” framed, whether reduced sequestration increased 6 make calculations results contested? then focuses particularly analyses producing appropriate context applying methods outlined. There particular focus our understanding temporal aspects feedstocks. This issue noted one debt, foregone sequestration, perhaps differently balance. Finally 7 implications initiatives “How frameworks incentivize synthesizes promoting emphasizes importance some recognizes need better understand food-fuel interface climate development. also identifies gap knowledge surrounding forest management perceives closer examination dynamics. notes fact importing effectively exporting obligations, occurs sectors imports goods.