Assessing the Climate Change Impacts of Biogenic Carbon in Buildings: A Critical Review of Two Main Dynamic Approaches

Environmental Life Cycle Assessment of a Novel Hemp-Based Building Material

The global construction sector contributes a significant share of total greenhouse gas (GHG) emissions. In Australia, infrastructure activity alone generates 18% of the GHG emissions. The use of low-embodied carbon building materials is crucial to decarbonise the construction sector and fulfil national and international climate goals. Industrial hemp (Cannabis sativa L.) is a promising feedstock for low-carbon construction materials because of its carbon sequestration capacity, fast-growing cycles, and technical functionality comparable to traditional materials. This study utilised the life cycle assessment (LCA) guideline ISO 14040:2006 to estimate the carbon footprint (CF) of hemp-based building materials in Western Australia capturing region-specific variations in terms of inputs, soil, productivity, and energy mix. The functional unit was 1 m2 of a hemp-based board, and the system boundary was cradle-to-gate, i.e., pre-farm, on-farm, and post-farm activities. The CF of 1 m2 of hemp-based board was estimated to be -2.302 kg CO2 eq. Electricity from the public grid for bio-based binder production during the post-farm stage was the main contributor to total CO2 eq emissions (26%), followed by urea production (14%) during the pre-farm stage. Overall, the use of electricity from the public grid during the post-farm stage accounted for 45% of total emissions. Sensitivity analysis showed that the CF of hemp-based boards was highly sensitive to the source of energy; i.e., total replacement of the public grid by solar power decreased the CF by 164% (-2.30 to -6.07 kg CO2 eq). The results suggested that hemp-based boards exhibit lower embodied GHG emissions compared to traditional materials, such as gypsum plasterboards.

Carbon balance of plywood from a social reforestation program in Indonesia

Social reforestation programs plant trees on degraded, uncultivated land in low-income regions to allow the local population to generate income from selling wood products and-in case of agroforestry systems-to grow food. For fundraising it is of interest to demonstrate not only positive social impacts but also environmental ones. Proving negative greenhouse gas (GHG) emissions would allow the programs to enter the market for carbon offsetting projects and liberate further funding. In a case study, a social reforestation program in Kalimantan, Indonesia, is analyzed. GHG emissions (according to ISO 14067, PAS 2050 and EU ILCD Handbook for LCA) of the main product, laminated veneer lumber plywood, are determined as 622 and 21 kg CO2-e/m3 for short-term and long-term (above 100 years) plywood use, respectively. Switching to lignin-based resins and renewable electricity could reduce emissions down to - 363 kg CO2-e/m3 for long-term use. The analyzed agroforestry system produces almost carbon-neutral plywood today and could be climate positive in the mid-term.

California's harvested wood products: A time-dependent assessment of life cycle greenhouse gas emissions

Following life-cycle assessment (LCA) methodology, this study presents a state-level estimation of embodied carbon of wood products harvested in 2019 from California and subsequently processed, manufactured, transported, used, and disposed at the end-of-life (EoL). In a conventional static approach to LCA, all GHG emissions were aggregated and considered to occur at year 0 of the given time horizon (500 years in this study) and used a static characterization factor (CF). In dynamic LCA, GHG emissions occurring in different years were considered, and their global warming impact (GWI) was determined using a time-dependent CF over the selected time horizon of 500 years. Four scenarios were developed to examine the impact of EoL choices on GWI. It was found that dynamic GWI for all scenarios ranged from 0.27 to 0.93 million tonne CO₂e, which were 45-73 % lower than those estimated with static LCA approach, indicating that the static LCA approach could lead to an underestimation of the benefits of substituting wood for non-wood products, compared to those based on dynamic LCA approach. This analysis also demonstrated that the choice of EoL treatment option is a key factor affecting the estimated GWI as it directly determines the annual emission of GHGs released into atmosphere and subsequently their warming effect depending on the time harvested wood products (HWPs) spend in the horizon of assessment. Overall, the dynamic LCA performed in this study enabled more robust interpretations of embodied carbon by including temporal boundaries associated with the HWPs life cycle.

Environmental advantages of coproducing beef meat in dairy systems

Beef meat, one of the more environmentally costly animal-based foods, can be produced in two general ways, as the main product on specialised farms or as a co-product on dairy farms. In this study, two cases (a semi-confinement dairy farm (A) and a pasture-based dairy farm (B)) have been analysed by means of LCA to evaluate the environmental impacts associated with the coproduction of beef meat. In both cases, purchased feed production was found to be the main cause of environmental impacts in most of the categories considered. Additionally, cow emissions to air were the main contributor for the global warming category. Comparing the two dairy systems, notably lower environmental impacts were obtained for B in 13 of the 18 categories analysed. Regarding CF, 8.10 and 8.88 kg CO₂eq/kg LW were obtained for A and B, respectively. These CF values were within the wide range found in the literature for beef meat (1.2-42.6 kg CO₂eq/kg LW). Beef calves and cull cows are an important output of dairy farming, so that coproduction enables milk and meat with lower CF and associated environmental impacts to be obtained. In addition, the variability of the data found in literature and the lack of LCA studies based on real data for beef meat coproduced on dairy farms evidence the importance of in-depth study of this interesting topic.

Carbon Footprint Assessment of a Novel Bio-Based Composite for Building Insulation

This research explores the carbon removal of a novel bio-insulation composite, here called MycoBamboo, based on the combination of bamboo particles and mycelium as binder. First, an attributional life cycle assessment (LCA) was performed to define the carbon footprint of a European bamboo plantation and a bio-insulation composite, as well as its ability to remove CO2 along its lifecycle at a laboratory scale. Secondly, the Global Worming Potential (GWP) was estimated through a dynamic LCA with selected end-of-life and technical replacement scenarios. Finally, a building wall application was analyzed to measure the carbon saving potential of the MycoBamboo when compared with alternative insulation materials applied as an exterior thermal insulation composite system. The results demonstrate that despite the negative GWP values of the biogenic CO2, the final Net-GWP was positive. The technical replacement scenarios had an influence on the final Net-GWP values, and a longer storage period is preferred to more frequent insulation substitution. The type of energy source and the deactivation phase play important roles in the mitigation of climate change. Therefore, to make the MycoBamboo competitive as an insulation system at the industrial scale, it is fundamental to identify alternative low-energy deactivation modes and shift all energy-intensity activities during the production phase to renewable energy.

From Nearly Zero Energy to Carbon-Neutral: Case Study of a Hospitality Building

In recent years, many cities around the world have pledged to upgrade their building stocks to carbon-neutral. However, the literature does not yet provide a shared definition of carbon-neutral building (CNB), and the assessment objectives and methodological approaches are vague and fragmented. Starting from the available standards and scientific literature on life cycle assessment (LCA), this paper advances an operational definition for CNB on the basis of an explicit calculation approach. It then applies the definition to an urban case study, comparing it against a state-of-the-art nearly Zero Energy Building (nZEB) scenario, with the intent of highlighting the major practical limitations connected to the application of a methodologically sound carbon neutrality calculation. The case study shows that carbon neutral objectives can hardly be achieved by single urban buildings because of the lack of spaces that can provide onsite carbon offsetting actions. Carbon neutrality may be better approached at the city, regional, or national scales, where overarching policies may be defined.

Life cycle assessment (LCA): informing the development of a sustainable circular bioeconomy?

The role of life cycle assessment (LCA) in informing the development of a sustainable and circular bioeconomy is discussed. We analyse the critical challenges remaining in using LCA and propose improvements needed to resolve future development challenges. Biobased systems are often complex combinations of technologies and practices that are geographically dispersed over long distances and with heterogeneous and uncertain sets of indicators and impacts. Recent studies have provided methodological suggestions on how LCA can be improved for evaluating the sustainability of biobased systems with a new focus on emerging systems, helping to identify environmental and social opportunities prior to large R&D investments. However, accessing economies of scale and improved conversion efficiencies while maintaining compatibility across broad ranges of sustainability indicators and public acceptability remain key challenges for the bioeconomy. LCA can inform, but not by itself resolve this complex dimension of sustainability. Future policy interventions that aim to promote the bioeconomy and support strategic value chains will benefit from the systematic use of LCA. However, the LCA community needs to develop the mechanisms and tools needed to generate agreement and coordinate the standards and incentives that will underpin a successful biobased transition. Systematic stakeholder engagement and the use of multidisciplinary analysis in combination with LCA are essential components of emergent LCA methods. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Assessment models and dynamic variables for dynamic life cycle assessment of buildings: a review

Life cycle assessment (LCA) is widely used to quantify the environmental performance of buildings. Recently, the potential temporal variations in the lifetime of buildings and their influences on assessment results have attracted considerable attention. Dynamic LCA (DLCA) is an emerging research topic. This study provides an overview of the current scenario of DLCA studies in the building field. A literature survey was conducted by searching through scientific literature databases; 48 articles met the inclusion criteria. Eleven dynamic variables as well as their addressing approaches were summarized and analyzed. A few typical dynamic assessment models were synthesized and compared to present the methodology progress. Finally, considering the existing limitations, a few research directions were recommended: setting cutoff criteria for dynamic variables, developing a dynamic database, and considering the interactions between dynamic variables. The analyses in this study indicate that research on the DLCA of buildings needs interdisciplinary cooperation. This review promotes in-depth understanding about DLCA research of buildings and offers valuable implications for environmental practice. The highlighted future research directions facilitate further explorations in this research area.

A State of the Art of the Overall Energy Efficiency of Wood Buildings-An Overview and Future Possibilities

The main goal of this study was to review current studies on the state of the art of wood constructions with a particular focus on energy efficiency, which could serve as a valuable source of information for both industry and scholars. This review begins with an overview of the role of materials in wood buildings to improve energy performance, covering structural and insulation materials that have already been successfully used in the market for general applications over the years. Subsequently, studies of different wood building systems (i.e., wood-frame, post-and-beam, mass timber and hybrid constructions) and energy efficiency are discussed. This is followed by a brief introduction to strategies to increase the energy efficiency of constructions. Finally, remarks and future research opportunities for wood buildings are highlighted. Some general recommendations for developing more energy-efficient wood buildings are identified in the literature and discussed. There is a lack of emerging construction concepts for wood-frame and post-and-beam buildings and a lack of design codes and specifications for mass timber and hybrid buildings. From the perspective of the potential environmental benefits of these systems as a whole, and their effects on energy efficiency and embodied energy in constructions, there are barriers that need to be considered in the future.

Comparative Cradle-to-Grave Life Cycle Assessment of Low and Mid-Rise Mass Timber Buildings with Equivalent Structural Steel Alternatives

The objective of this paper was to quantify and compare the environmental impacts associated with alternative designs of typical North American low and mid-rise buildings. Two scenarios were considered: a traditional structural steel frame or an all-wood mass timber design, utilizing engineered wood products for both gravity and lateral load resistance. The boundary of the quantitative analysis was cradle-to-grave with considerations taken to discuss end-of-life and material reuse scenarios. The TRACI methodology was followed to conduct a Life Cycle Impact Assessment (LCIA) analysis that translates building quantities to environmental impact indicators using the Athena Impact Estimator for Buildings Life Cycle analysis software tool and Athena’s Life Cycle Inventory database. The results of the analysis show that mass timber buildings have an advantage with respect to several environmental impact categories, including eutrophication potential, human health particulate, and global warming potential where a 31% to 41% reduction was found from mass timber to steel designs, neglecting potential carbon sequestration benefits from the timber products. However, it was also found that the steel buildings have a lower impact with respect to the environmental impact categories of smog potential, acidification potential, and ozone depletion potential, where a 48% to 58% reduction was found from the steel to the mass timber building designs.

Addressing temporal considerations in life cycle assessment

In life cycle assessment (LCA), temporal considerations are usually lost during the life cycle inventory calculation, resulting in an aggregated "snapshot" of potential impacts. Disregarding such temporal considerations has previously been underlined as an important source of uncertainty, but a growing number of approaches have been developed to tackle this issue. Nevertheless, their adoption by LCA practitioners is still uncommon, which raises concerns about the representativeness of current LCA results. Furthermore, a lack of consistency can be observed in the used terms for discussions on temporal considerations. The purpose of this review is thus to search for common ground and to identify the current implementation challenges while also proposing development pathways. This paper introduces a glossary of the most frequently used terms related to temporal considerations in LCA to build a common understanding of key concepts and to facilitate discussions. A review is also performed on current solutions for temporal considerations in different LCA phases (goal and scope definition, life cycle inventory analysis and life cycle impact assessment), analysing each temporal consideration for its relevant conceptual developments in LCA and its level of operationalisation. We then present a potential stepwise approach and development pathways to address the current challenges of implementation for dynamic LCA (DLCA). Three key focal areas for integrating temporal considerations within the LCA framework are discussed: i) define the temporal scope over which temporal distributions of emissions are occurring, ii) use calendar-specific information to model systems and associated impacts, and iii) select the appropriate level of temporal resolution to describe the variations of flows and characterisation factors. Addressing more temporal considerations within a DLCA framework is expected to reduce uncertainties and increase the representativeness of results, but possible trade-offs between additional data collection efforts and the increased value of results from DLCAs should be kept in mind.

Life Cycle Assessment of Prefabricated Geopolymeric Façade Cladding Panels Made from Large Fractions of Recycled Construction and Demolition Waste

The construction and demolition sector is one of the biggest consumers of natural resources in the world and consequently, one of the biggest waste producers worldwide. The proper management of construction and demolition waste (CDW) can provide major benefits for the construction and recycling industry. However, the recycling rate of CDW is relatively low, as there is still a lack of confidence in the quality of recycled CDW materials. Therefore, new research projects are looking for innovative solutions within recycling of CDW in order to overcome uncertainties currently associated with the use of construction products made from recycled or re-used CDW. In this paper, a “cradle-to-cradle” life cycle assessment (LCA) study has been conducted to investigate the environmental performance of the prefabricated geopolymeric façade cladding panels made from large fractions of CDW. The LCA results indicate that the majority of the environmental burden arises within the manufacturing stage; however, the environmental burden can be reduced with simple optimisation of the manufacturing process. Furthermore, the environmental impact of the prefabricated geopolymeric façade cladding panels is generally lower than the environmental burden associated with the façade cladding panels made from virgin materials.

More Timber in Construction: Unanswered Questions and Future Challenges

The built environment is one of the greatest contributors to carbon emissions, climate change, and to the unsustainable pressure on the natural environment and its ecosystems. The use of more timber in construction is one possible response, and an authoritative contribution to this growing movement comes from the UK’s Committee on Climate Change, which identifies a “substantial increase in the use of wood in the construction of buildings” as a top priority. However, a global encouragement of such a strategy raises some difficult questions. Given the urgency of effective solutions for low-carbon built environments, and the likely continued growth in demand for timber in construction, this article reviews its sustainability and identifies future challenges and unanswered questions. Existing evidence points indeed towards timber as the lower carbon option when modelled through life cycle assessment without having to draw on arguments around carbon storage. Issues however remain on the timing of carbon emissions, land allocation, and the environmental loads and benefits associated with the end-of-life options: analysis of environmental product declarations for engineered timber suggests that landfill might either be the best or the worst option from a climate change perspective, depending on assumptions.

Assessment of the Impact of Climate Change Policies on the Market for Forest Industrial Residues

As part of the Pan-Canadian Framework (PCF) on Clean Growth and Climate Change, the Government of Canada (GoC) introduced carbon pricing and is in the process of developing a Clean Fuel (CF) Standard. Both policies are key elements of the PCF and aim to reduce greenhouse gas (GHG) emissions through the use of lower carbon fuels, including bioenergy. Carbon pricing and the CF Standard are expected to increase the demand for biomass feedstocks, possibly threatening feedstock availability for existing forest industrial residues users, including composite panel manufacturers. To assess the potential impact of carbon pricing and the CF Standard on Canadian composite panel producers, a Monte Carlo-based model was developed to estimate possible increases in feedstock price-points that composite panel manufacturers may face as a result of increases in bioenergy consumption. Results suggest that the composite panel industry may be negatively impacted in the long-term (2030) by the relative price increase of fossil fuels covered by carbon pricing and additional revenues for biofuel suppliers from CF Standard credits, assuming no other adjustments to the market. Although these results are preliminary in that the analysis excludes external market factors that could influence the outcome, there is evidence that such policies have the potential to generate supply risks for the Canadian composite panel industry without careful consideration of the associated externalities.

Overview on GHG emissions of raw milk production and a comparison of milk and cheese carbon footprints of two different systems from northern Spain

Milk production has been estimated to contribute 3-4% of anthropogenic greenhouse gas (GHG) emissions. However, the carbon footprint associated with raw milk can vary, depending on a variety of factors, such as the geographical area, species of cow and production system. In this study, a global overview of research published on the carbon footprint (CF) of raw cow milk is provided. Additionally, two different dairy systems (semi-confinement and pasture-based) have been analysed by life-cycle assessment (LCA) in order to determine their effect on the CF of the milk produced. Inventory data were obtained directly from these facilities, and the main factors involved in milk production were included (co-products, livestock food, water, electricity, diesel, cleaning elements, transport, manure and slurry management, gas emissions to air etc.). In agreement with reviewed literature, it was found that the carbon footprint of milk was basically determined by the cattle feeding system and gas emissions from the cows. The values of milk CF found in the systems under study were within the range for cow milk production worldwide (0.9-4.7 kgCO₂eq kg_FPCM^-1). Specifically, in the semi-confinement and the pasture-based dairy farms, 1.22 and 0.99 kgCO₂eq kg_FPCM^-1 were obtained, respectively. The environmental benefits obtained with the pasture grazing system are not only mainly due to the lower use of purchased fodder but also to the allocation between milk and meat that was found to be a determining methodological factor in CF calculation. Finally, data from the evaluated dairy systems have been employed to analyse the influence of raw milk production on cheese manufacturing. With this aim, the CF of a small-scale cheese factory has also been obtained. The main subsystems involved (raw materials, water, electricity, energy, cleaning products, packaging materials, transport, wastes and gas emissions) were included in the inventory of the cheese factory. CF values were 16.6 and 14.7 kgCO₂eq kg^-1 of cheese for milk produced in semi-confinement and pasture-based systems, respectively. The production of raw milk represented more than 60% of CO₂eq emissions associated with cheese, so the primary production is the critical factor in reducing the GHG emissions due to cheese making.

The Future of Ex-Ante LCA? Lessons Learned and Practical Recommendations

Every decision-oriented life cycle assessment (LCAs) entails, at least to some extent, a future-oriented feature. However, apart from the ex-ante LCAs, the majority of LCA studies are retrospective in nature and do not explicitly account for possible future effects. In this review a generic theoretical framework is proposed as a guideline for ex-ante LCA. This framework includes the entire technology life cycle, from the early design phase up to continuous improvements of mature technologies, including their market penetration. The compatibility with commonly applied system models yields an additional aspect of the framework. Practical methods and procedures are categorised, based on how they incorporate future-oriented features in LCA. The results indicate that most of the ex-ante LCAs focus on emerging technologies that have already gone through some research cycles within narrowly defined system boundaries. There is a lack of attention given to technologies that are at a very early development stage, when all options are still open and can be explored at a low cost. It is also acknowledged that technological learning impacts the financial and environmental performance of mature production systems. Once technologies are entering the market, shifts in market composition can lead to substantial changes in environmental performance.

Comparative analyses of different biogenic CO2 emission accounting systems in life cycle assessment

The biomass-derived CO₂ emission is usually treated as neutral to climate change. However, due to the stay of biomass-derived CO₂ in the atmosphere, many researchers believe that biomass-derived CO₂ also has climate change benefit. Therefore, many methods to account the global warming potential of biomass-derived CO₂ (GWP_bio) were proposed. Based on those new methods, we developed an accounting system for climate change impact of biomass utilization in this study, and compared it with the conventional accounting system which follows the carbon neutral assumption. A case study of caragana-to-pellet bioenergy production system was simulated to test the performance of the GWP_bio accounting system. The CENTURY model was used to simulate carbon dynamics of caragana plantation in the Loess Plateau in China, and life cycle assessment (LCA) model was developed to estimate the life cycle emissions of the caragana-to-pellet system. Attributed to short rotation of caragana plantation and fast biomass accumulation after harvest, the GWP_bio values around 0.044 were obtained. When the GWP_bio was applied to LCA, significant high life cycle CO₂ emission was found in comparison to the conventional method. However, the GWP_bio accounting system has lower positive climate change impact than the conventional accounting system in assessing the overall impact of biomass utilization. This indicated that the application of GWP_bio accounting system would encourage the utilization of biomass and allow a fair comparison with fossil fuels. In the sensitivity analysis, we found the accounting system was sensitive to biomass accumulation and all the corresponding factor affecting biomass accumulation.

Energy and Environmental Aspects of Using Eucalyptus from Brazil for Energy and Transportation Services in Europe

The international market of woody biomass for bioenergy is expected to have a major role in future global scenarios aligning with a 2 or 1.5 °C target. However, the quantification of the environmental impacts of energy and transportation services from novel technologies and biomass production systems are yet to be extensively studied on a case-specific basis. We use a life cycle assessment approach to quantify environmental impacts of four bioenergy systems based on eucalyptus plantations established in abandoned pastureland in Brazil. The alternative bioenergy systems deliver energy and transportation services in Europe (cradle-to-gate analysis), including modern technologies for production of heat, electricity (with and without carbon capture and storage), and advanced liquid biofuels. We find that all bioenergy systems can achieve sizeable climate benefits, but in some cases at increased pressure in other impact categories. The most impacting activities are biomass transport stages, followed by eucalyptus stand establishment, and pellet production. An estimate of the potential large-scale bioenergy deployment of eucalyptus established in marginal areas in Brazil shows that up to 7 EJ of heat, 2.5 EJ of electricity, or 5 EJ of transportation biofuels per year can be delivered. This corresponds to a climate mitigation potential between 0.9% and 2.4% (0.29 and 0.83 GtCO2 per year) of the global anthropogenic emissions in 2015, and between 5.7% and 16% of European emissions, depending on the specific bioenergy system considered. A sensitivity analysis indicated that the best environmental performance is achieved with on-site biomass storage, transportation of wood chips with trucks, pellets as energy carrier, and larger ship sizes. Our quantitative environmental analysis contributes to increased understanding of the potential benefits and tradeoffs of large-scale supply of biomass resources, and additional research can further improve resolution and integrate environmental impact indicators within a broader sustainability perspective, as indicated by the recently established sustainable development goals.

Contribution of forest wood products to negative emissions: historical comparative analysis from 1960 to 2015 in Norway, Sweden and Finland

BACKGROUND

Forests and forest products can significantly contribute to climate change mitigation by stabilizing and even potentially decreasing the concentration of carbon dioxide (CO₂) in the atmosphere. Harvested wood products (HWP) represent a common widespread and cost-efficient opportunity for negative emissions. After harvest, a significant fraction of the wood remains stored in HWPs for a period that can vary from some months to many decades, whereas atmospheric carbon (C) is immediately sequestered by vegetation re-growth. This temporal mismatch between oxidation of HWPs and C uptake by vegetation generates a net sink that lasts over time. The role of temporary carbon storage in forest products has been analysed and debated in the scientific literature, but detailed bottom-up studies mapping the fate of harvested materials and quantifying the associated emission profiles at national scales are rare. In this work, we quantify the net CO₂ emissions and the temporary carbon storage in forest products in Norway, Sweden and Finland for the period 1960-2015, and investigate their correlation. We use a Chi square probability distribution to model the oxidation rate of C over time in HWPs, taking into consideration specific half-lives of each category of products. We model the forest regrowth and estimate the time-distributed C removal. We also integrate the specific HWP flows with an emission inventory database to quantify the associated life-cycle emissions of fossil CO₂, CH₄ and N₂O.

RESULTS

We find that assuming an instantaneous oxidation of HWPs would overestimate emissions of about 1.18 billion t CO₂ (cumulative values for the three countries over the period 1960-2015).We also find that about 40 years after 1960, the starting year of our analysis, are sufficient to detect signs of negative emissions. The total amount of net CO₂ emissions achieved in 2015 are about - 3.8 million t CO₂, - 27.9 t CO₂ and - 43.6 t CO₂ in Norway, Sweden, and Finland, respectively.

CONCLUSION

We argue for a more explicit accounting of the actual emission rates from HWPs in carbon balance studies and climate impact analysis of forestry systems and products, and a more transparent inclusion of the potential of HWP as negative emissions in perspective studies and scenarios. Simply assuming that all harvested carbon is instantaneously oxidized can lead to large biases and ultimately overlook the benefits of negative emissions of HWPs.