Time-Dynamic Effects on the Global Temperature When Harvesting Logging Residues for Bioenergy
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Time-Dynamic Effects on the Global Temperature When Harvesting Logging Residues for Bioenergy Torun Hammar 1 & Carina A. Ortiz 2 & Johan Stendahl 2 & Serina Ahlgren 1 & Per-Anders Hansson 1
Published online: 4 July 2015 # Springer Science+Business Media New York 2015
Abstract The climate mitigation potential of using logging residues (tree tops and branches) for bioenergy has been debated. In this study, a time-dependent life cycle assessment (LCA) was performed using a single-stand perspective. Three forest stands located in different Swedish climate zones were studied in order to assess the global temperature change when using logging residues for producing district heating. These systems were compared with two fossil reference systems in which the logging residues were assumed to remain in the forest to decompose over time, while coal or natural gas was used for energy. The results showed that replacing coal with logging residues gave a direct climate benefit from a single-stand perspective, while replacing natural gas gave a delayed climate benefit of around 8–12 years depending on climate zone. A sensitivity analysis showed that the time was strongly dependent on the assumptions for extraction and combustion of natural gas. The LCA showed that from a single-stand perspective, harvesting logging residues for bioenergy in the south of Sweden would give the highest temperature change mitigation potential per energy unit. However, the differences between the three climate zones studied per energy unit were relatively small. On a hectare basis, the southern forest stand would generate more biomass compared to the central and northern locations, which thereby could replace more fossil fuel and give larger climate benefits.
* Torun Hammar [email protected] 1
Department of Energy and Technology, Swedish University of Agricultural Sciences (SLU), Uppsala SE-750 07, Sweden
2
Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), Uppsala SE-750 07, Sweden
Keywords Life cycle assessment . Soil organic carbon . Global warming . Boreal forest . Biogenic carbon . Greenhouse gas emissions
Introduction Climate change is an important issue which needs to be addressed. According to the latest Intergovernmental Panel on Climate Change (IPCC) report, the human-induced emissions of greenhouse gases (GHGs) are the major drivers behind climate change [1]. Reducing GHG emissions is therefore central for mitigating climate change. However, how to reduce these GHG emissions is debated. One proposed strategy is to replace fossil fuels with bioenergy [2]. In the European Union (EU), targets for reducing the release of GHGs have been adopted by the member countries. These goals are referred to as the ‘20-20-20’ targets and include a 20 % decrease of the GHG emissions in the EU, and an increase to 20 % of renewable energy, by year 2020 (compared to year 1990) [3]. Sweden has higher mitigation targets during the same timeframe with a 40 % reduction in GHG emissions and a goal to increase renewable ener
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