Time-dependent climate impact of biomass use in a fourth generation district heating system, including BECCS

Changes to energy systems are needed in order to reduce greenhouse gas emissions and mitigate climate change. This study assessed the climate change mitigation potential, in terms of temperature change over time, of a new combined heat and power (CHP) plant, including the dynamic effect on an existing fourth generation district heating system. The climate impact of combusting forest residues (tops and branches) was compared with combusting municipal solid waste (MSW), waste wood or hard coal. A scenario with wood chip combustion and carbon capture and storage (BECCS) was also assessed. The district heating system in Stockholm, Sweden, was used as a case study for the assessment. The results clearly show climate change mitigation potential of combusting wood chips, compared with hard coal and MSW, with this climate benefit increasing further with BECCS. The results also demonstrate the importance of time dynamic effects in the energy system and temperature response, highlighting the importance of not postponing implementation of climate change mitigation options if agreed climate targets are to be met on time

Temporal climate impacts of using willow and logging residues for district heating in Sweden

Using bioenergy to replace fossil fuels has been adopted as a climate mitigation measure, since less greenhouse gases are expected to be released into the atmosphere. In Sweden, the share of bioenergy is relative high (about 23% of total consumption including peat), with a relatively large proportion originating from domestically produced forest biomass. This thesis examined the climate impact of using two types of woody biomass (willow, logging residues) for district heating, using time-dependent life cycle assessment methodology. The climate impact of the wood-based energy systems was determined and compared with that of the fossil fuels coal and natural gas. The focus was on the temporal dynamics of carbon fluxes between soil, biomass and atmosphere. Establishing willow on agricultural land provided the potential to sequester carbon from atmosphere to soil, giving a net cooling effect on global mean temperature. However, this effect was shown to be highly dependent on willow yield (i.e. productivity), with low yield potentially decreasing soil carbon content. Moreover, district heating from willow chips gave a lower warming effect than coal and natural gas, irrespective of yield. Combustion of forest biomass in the form of logging residues also gave a lower warming effect than coal and natural gas. However, the climate benefits compared with natural gas were delayed by 15-20 years (depending on geographical location) due to the chemical composition of natural gas, which generates less greenhouse gas emissions than coal and logging residues during extraction and combustion. Nevertheless, when decomposition of unharvested forest biomass was included in the reference systems, bioenergy from logging residues had climate benefits compared with coal and natural gas

Climate impacts of woody biomass use for heat and power production in Sweden

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)

Time-dependent climate impact of beef production - can carbon sequestration in soil offset enteric methane emissions?

The time-dependent climate impact of beef production, including changes in soil organic carbon, was examined in this study. A hypothetical suckler cow system located in south-east Sweden was analysed using a time dependent life cycle assessment method in which yearly fluxes of greenhouse gases were considered and the climate impact in terms of temperature response over time was calculated. The climate impact expressed as carbon dioxide equivalents, i.e. global warming potential in a 100-year time perspective, was also calculated. The Introductory Carbon Balance Model was used for modelling yearly soil organic carbon changes from land use. The results showed an average carbon sequestration rate of 0.2 Mg C ha(-1) and yr(-1), so carbon sequestration could potentially counteract 15-22% of emissions arising from beef production (enteric fermentation, feed production and manure management), depending on system boundaries and production intensity. The temperature response, which showed a high initial increase due to methane emissions from enteric fermentation, started to level off after around 50 years due to the short atmospheric lifetime of methane. However, sustained production and associated methane emissions would maintain the temperature response and contribute to climate damage. A forage-grain beef system resulted in a lower climate impact than a forage-only beef system (due to higher slaughter age), even though more carbon was sequestered in the forage-only system

Climate impact of willow grown for bioenergy in Sweden

Short-rotation coppice willow (SRCW) is a fast-growing and potentially high-yielding energy crop. Transition to bioenergy has been identified in Sweden as one strategy to mitigate climate change and decrease the current dependency on fossil fuel. In this study, life cycle assessment was used to evaluate and compare the climate impacts of SRCW systems, for the purpose of evaluating key factors influencing the climate change mitigation potential of SRCW grown on agricultural land in Sweden. Seven different scenarios were defined and analysed to identify the factors with the most influence on the climate. A carbon balance model was used to model carbon fluxes between soil, biomass and atmosphere under Swedish growing conditions. The results indicated that SRCW can act as a temporary carbon sink and therefore has a mitigating effect on climate change. The most important factor in obtaining a high climate change-mitigating effect was shown to be high yield. Low yield gave the worst mitigating effect of the seven scenarios, but it was still better than the effect of the reference systems, district heating produced from coal or natural gas

Climate effects of a forestry company : including biogenic carbon fluxes and substitution effects

Forestry will play an important role in a future bioeconomy, by providing wood fibres for biomaterial and bioenergy. However, there are contradictory opinions on the climate change mitigation potential of forestry. Stora Enso, an international forestry company, has the ambition to improve its climate impact assessment at corporate level. In this work, a system perspective was applied, where greenhouse gas emissions from value chains, biogenic carbon fluxes from forest land owned or leased by Stora Enso and temporarily stored in harvested wood products, and the substitution effect, i.e. avoided emissions from substituted products and energy were considered. Furthermore, new substitution factors for pulp and paper products were developed. The estimated climate effect at corporate level was a net removal of -11.5 million Mg CO2-eq yr-1 (i.e. a climate benefit) when considering value chain emissions, biogenic carbon fluxes from forest land and harvested wood products, and avoided emissions from substitution. Uptake of biogenic carbon counteracted around 40% of the value chain emissions, while the largest climate benefit (removal of 17.9 million Mg CO2-eq) was due to substitution of more greenhouse gas-intensive products. The new substitution factors developed for pulp and paper products were applied in the climate impact calculation at company level. Important assumptions and possible improvements for future studies were identified, e.g. how to assess the impact of cascading wood use in substitution calculations

Albedo impacts of current agricultural land use: Crop-specific albedo from MODIS data and inclusion in LCA of crop production

Agricultural land use and management practices affect the global climate due to greenhouse gas (GHG) fluxes and changes in land surface properties. Increased albedo has the potential to counteract the radiative forcing and warming effect of emitted GHGs. Thus considering albedo could be important to evaluate and improve agricultural systems in light of climate change, but the albedo of individual practices is usually not known. This study quantified the albedo of individual crops under regional conditions, and evaluated the importance of albedo change for the climate impact of current crop production using life cycle assessment (LCA). Seven major crops in southern Sweden were assessed relative to a land reference without cultivation, represented by semi-natural grassland. Crop-specific albedo data were obtained from a MODIS product (MCD43A1 v6), by combining its spatial response pattern with geodata on agricultural land use 2011–2020. Fluxes of GHGs were estimated using regional data and models, including production of inputs, field operations, and soil nitrogen and carbon balances. Ten-year mean albedo was 6–11% higher under the different crops than under the reference. Crop-specific albedo varied between years due to weather fluctuations, but differences between crops were largely consistent. Increased albedo countered the GHG impact from production of inputs and field operations by 17–47% measured in GWP100, and the total climate impact was warming. Using a time-dependent metric, all crops had a net cooling impact on global mean surface temperature on shorter timescales due to albedo (3–12 years under different crops), but a net warming impact on longer timescales due to GHG emissions. The methods and data presented in this study could support increasingly comprehensive assessments of agricultural systems. Further research is needed to integrate climatic effects of land use on different spatial and temporal scales, and direct and indirect consequences from a systems perspective

Nordic forest management towards climate change mitigation: time dynamic temperature change impacts of wood product systems including substitution effects

Climate change mitigation trade-offs between increasing harvests to exploit substitution effects versus accumulating forest carbon sequestration complicate recommendations for climate beneficial forest management. Here, a time dynamic assessment ascertains climate change mitigation potential from different rotation forest management alternatives across three Swedish regions integrating the forest decision support system Heureka RegWise with a wood product model using life cycle assessment data. The objective is to increase understanding on the climate effects of varying the forest management. Across all regions, prolonging rotations by 20% leads on average to the largest additional net climate benefit until 2050 in both, saved emissions and temperature cooling, while decreasing harvests by 20% leads to the cumulatively largest net climate benefits past 2050. In contrast, increasing harvests or decreasing the rotation period accordingly provokes temporally alternating net emissions, or slight net emission, respectively, regardless of a changing market displacement factor. However, future forest calamities might compromise potential additional temperature cooling from forests, while substitution effects, despite probable prospective decreases, require additional thorough and time explicit assessments, to provide more robust policy consultation

Nordic forest management towards climate change mitigation: time dynamic temperature change impacts of wood product systems including substitution effects

Climate change mitigation trade-offs between increasing harvests to exploit substitution effects versus accumulating forest carbon sequestration complicate recommendations for climate beneficial forest management. Here, a time dynamic assessment ascertains climate change mitigation potential from different rotation forest management alternatives across three Swedish regions integrating the forest decision support system Heureka RegWise with a wood product model using life cycle assessment data. The objective is to increase understanding on the climate effects of varying the forest management. Across all regions, prolonging rotations by 20% leads on average to the largest additional net climate benefit until 2050 in both, saved emissions and temperature cooling, while decreasing harvests by 20% leads to the cumulatively largest net climate benefits past 2050. In contrast, increasing harvests or decreasing the rotation period accordingly provokes temporally alternating net emissions, or slight net emission, respectively, regardless of a changing market displacement factor. However, future forest calamities might compromise potential additional temperature cooling from forests, while substitution effects, despite probable prospective decreases, require additional thorough and time explicit assessments, to provide more robust policy consultation

Climate effects of a forestry company – including biogenic carbon fluxes and substitution effects (2021 update)

Forestry play an important role in the bioeconomy, and will continues to do so in the future, by providing wood fibres for biomaterial and bioenergy that substitute for fossil-based alternatives, while at the same time storing carbon in forests and harvested wood products. However, there are contradictory opinions on the climate change mitigation potential of forestry. Stora Enso, an international forestry company, has the ambition to improve its climate impact assessment at corporate level. In this work, a system perspective was applied, where greenhouse gas emissions from value chains, biogenic carbon fluxes from forest land owned or leased by Stora Enso and temporarily stored in harvested wood products, and the substitution effect, i.e. avoided emissions from substituted products and energy were considered. Furthermore, new substitution factors for pulp and paper products were developed. The current report is an update of the original report, published in 2020 (Hammar et. al. 2020), based on production and value chain emissions data for the year 2021, as well as Eucalyptus plantation area as of December 2020. Overall changes in greenhouse gas fluxes relative the ones published in Hammar et al. (2020) are minor. The estimated climate effect at corporate level for 2021 is a net removal of -11.0 million Mg CO2-eq yr-1 (i.e. a climate benefit) for the year 2021 (compared to -11.5 million Mg CO2-eq yr-1 for the year 2019) when considering value chain emissions, biogenic carbon fluxes from forest land and harvested wood products, and avoided emissions from substitution. Uptake of biogenic carbon counteracted around 40% of the value chain emissions (10.2 million Mg CO2-eq yr-1), while the largest climate benefit (removal of 17.2 million Mg CO2-eq) was due to substitution of more greenhouse gas-intensive products. The same substitution factors developed in Hammar et al. (2020) for pulp and paper products were applied in the climate impact calculation at company level. Possible improvements for future studies inclued, e.g., the assessment of the impact of cascading wood use in substitution calculations