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- Hammar, Torun, et al.
(författare)
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Climate impact assessment of willow energy from a landscape perspective : A Swedish case study
- 2017
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Ingår i: Global Change Biology Bioenergy. - : John Wiley & Sons. - 1757-1693 .- 1757-1707. ; 9:5, s. 973-985
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Tidskriftsartikel (refereegranskat)abstract
- Locally produced bioenergy can decrease the dependency on imported fossil fuels in a region, while also being valuable for climate change mitigation. Short-rotation coppice willow is a potentially high-yielding energy crop that can be grown to supply a local energy facility. This study assessed the energy performance and climate impacts when establishing willow on current fallow land in a Swedish region with the purpose of supplying a bio-based combined heat and power plant. Time-dependent life cycle assessment (LCA) was combined with geographic information system (GIS) mapping to include spatial variation in terms of transport distance, initial soil organic carbon content, soil texture and yield. Two climate metrics were used [global warming potential (GWP) and absolute global temperature change potential (AGTP)], and the energy performance was determined by calculating the energy ratio (energy produced per unit of energy used). The results showed that when current fallow land in a Swedish region was used for willow energy, an average energy ratio of 30 MJ MJ-1 (including heat, power and flue gas condensation) was obtained and on average 84.3 Mg carbon per ha was sequestered in the soil during a 100-year time frame (compared with the reference land use). The processes contributing most to the energy use during one willow rotation were the production and application of fertilizers (~40%), followed by harvest (~35%) and transport (~20%). The temperature response after 100 years of willow cultivation was -6·10-16K MJ-1 heat, which is much lower compared with fossil coal and natural gas (70·10-16K MJ-1 heat and 35·10-16 K MJ-1 heat, respectively). The combined GIS and time-dependent LCA approach developed here can be a useful tool in systematic analysis of bioenergy production systems and related land use effects.
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| 2. |
- Hammar, Torun
(författare)
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Climate impacts of woody biomass use for heat and power production in Sweden
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is a result of human-induced greenhouse gas emissions, primarily from fossil fuel use, but also from land use changes. To mitigate climate change, fossil fuel-based energy systems need to be replaced with alternative energy sources. Here bioenergy can play an important role, since this renewable fuel is considered to be carbon-neutral, meaning that no extra carbon dioxide (CO2) is emitted to the atmosphere. However, carbon-neutral is not the same as climate-neutral and, while the CO2 from biomass use was once, and will again, be captured during plant growth, the temporary imbalance in the atmosphere can have consequences for the climate. Furthermore, bioenergy supply chains generally consume fossil fuels and producing biomass for energy requires land, which can lead to carbon stock changes. This thesis examined the climate impact and energy performance of bioenergy from short-rotation coppice willow and long-rotation forest residues. Willow is a dedicated energy crop grown on agricultural land for energy, while forest residues (tops, branches and stumps) are a by-product harvested after final felling in conventional forests. A time-dependent life cycle assessment (LCA) method was used to capture the timing of greenhouse gas fluxes, including biogenic carbon (carbon stored in biomass and soil). In addition, a new method that combines time-dependent LCA with GIS mapping, and thus assesses the climate impact over a landscape, was developed. The results showed that growing willow on former fallow land can give a negative climate impact (cooling effect) by sequestering carbon from the atmosphere in biomass and soil and by achieving high productivity, which is important for the final outcome. Initial soil organic carbon content was shown to have a large influence on future carbon stocks. Harvesting forest residues for energy gave a higher climate impact than harvesting willow, with forest stumps giving a slightly higher climate impact than tops and branches. Moreover, forest residues harvested in northern Sweden gave a slightly higher climate impact than forest residues harvested in the south. All bioenergy feedstocks studied gave a lower climate impact than hard coal and natural gas over time and the climate benefit of replacing these fossil fuels increased over time when studying continuous energy outtake (landscape perspective).
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| 3. |
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| 4. |
- Snäll, Tord, et al.
(författare)
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Transient trade-off between climate benefit and biodiversity loss of harvesting stumps for bioenergy
- 2017
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Ingår i: Global Change Biology Bioenergy. - : WILEY. - 1757-1693 .- 1757-1707. ; 9:12, s. 1751-1763
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Tidskriftsartikel (refereegranskat)abstract
- To replace fossil fuel and thereby mitigate climate change, harvesting of wood such as stumps for bioenergy will likely increase. Coarse deadwood is an important resource for biodiversity and stumps comprise the main part of the coarse deadwood in managed forests. We provide the first integrated analysis of the long-term climate and biodiversity impacts of a whole landscape. We simultaneously project climate and biodiversity impacts of harvesting stumps to substitute for fossil coal, assuming scenarios with different proportions of the landscape with stump harvest (10, 50, 80%) the coming 50years. A life cycle approach was used to calculate future global temperature changes and future metapopulation changes in six epixylic lichens. Metapopulation dynamics were projected using colonization and extinction models based on times series data. Harvesting stumps from 50% of the clear-cut forest land benefits climate with a net global temperature reduction >0.5.10(-9)Kha(-1) after 50years if assuming substitution of fossil coal. For all scenarios, using stump bioenergy leads to immediate (within 1year) reductions in temperature of >= 50% compared to using fossil coal, increasing to 70% reduction after 50 years. However, large-scale stump harvest inflicted substantial metapopulation declines for five of six lichens. High stump harvest levels (>= 50%) put common lichens at risk of becoming red-listed following the IUCN criteria. The net temperature reduction (cooling effect) from substituting fossil coal with stumps harvested for bioenergy increased over time, while lichen metapopulations stabilized at lower equilibria after two to three decades. This indicates that trade-offs between climate and metapopulations of commons species are transient, where climate benefits become more prevalent in the long term. As both objectives are important for meeting (inter-)national climate and biodiversity targets, integrated analyses such as this should be encouraged and urged to guide policymaking about large-scale implementation of stump harvest.
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