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Existing assessments of climate mitigation technologies, like carbon capture utilisation and storage (CCUS), often rely on life cycle assessments (LCA), which are helpful for quantification but may not always be the most complete tools for decision-making. The novel contribution of this study is to provide the first application of a consequential carbon accounting approach, presented as a time-series analysis, to measure the system-wide change in emissions from CCUS linked to CO 2 -enhanced oil recovery. This method includes emissions from marginal oil production, a variable typically excluded in other LCA methods. The method was applied to a hypothetical CCUS project in Mexico to understand critical factors determining whether such an intervention can effectively contribute to emissions reduction in alignment with net-zero goals. Four intervention scenarios were assessed, comparing two distinct CO 2 injection strategies in oil reservoirs (water alternating gas and continuous gas injection) and two energy policy scenarios (current and sustainability). The findings suggest that the energy grid's role in overall emissions is relatively minor, with only a ∼2% difference between the compared scenarios, in contrast, the injection strategy has a significant impact on emissions. Scenarios 1 and 3 report a total change in emissions of −28.39 and −29.87MtCO 2 e, and scenarios 2 and 4 account for −19.63 and −21.22MtCO 2 e, respectively. The results highlight the importance of conducting system-wide analysis and comparing different scenarios to identify the critical components that drive changes in emissions and, therefore, support decision-making and project planning. • Consequential carbon accounting quantifies the system-wide change caused by CCUS. • A time-series provides decision-relevant information on climate change mitigation. • Market-mediated effects are highly relevant for CCUS projects. • CCUS is not consistent with net zero due to as remaining emissions. [ABSTRACT FROM AUTHOR]

Bioenergy with carbon capture and storage (BECCS) is regarded as a crucial negative emission technology (NET) in many prospective climate change mitigation scenarios that limit global warming below 2 °C. However, there is still insufficient understanding of the overall life cycle environmental performance of different BECCS configurations. Despite the fact that BECCS entails many technological combinations, the technology is still regarded as a single "black box" technology in most climate scenarios. This study presents a critical review of life cycle assessment (LCA) on a wide range of BECCS options: biomass direct-fired power generation, biomass gasification power generation, bio-hydrogen production, biomass application in industry sectors and other biomass conversion processes, such as pyrolysis and fermentation. It is evident from the review that the biomass direct-fired and gasification power plant with a 100% biomass firing ratio and the gasification-based bio-hydrogen processes have a strong potential to achieve negative emissions. However, the net negative life cycle emissions range widely among studies for each configuration due to variations in technology, LCA methodology and assumptions. Additionally, there is an insufficient assessment of comprehensive environmental impacts for BECCS systems other than GWP, making it still unclear about the trade-offs between the benefit from climate change mitigation and potential negative impacts. Main recommendations for improving LCA on BECCS include developing a generalized guideline and standardization for BECCS LCA, conducting LCAs with comprehensive impact categories, focusing on BECCS configurations being overlooked, considering the impact of land use change and the global warming potential of biomass, and extending LCA in both temporal and spatial dimension. [Display omitted] • Systematically review of life cycle assessment on BECCS systems. • Detailed review on various biomass conversion technologies. • Net negative life cycle emissions range widely among studies. • Insufficient studies of some biomass conversion pathways. • Insufficient studies on multi-environmental environment impact categories. [ABSTRACT FROM AUTHOR]

Wood and other bio-based building materials are often perceived as a good choice from a climate mitigation perspective. This article compares the life cycle assessment of the same multi-residential building from the perspective of 16 countries participating in the international project Annex 72 of the International Energy Agency to determine the effects of different datasets and methods of accounting for biogenic carbon in wood construction. Three assessment methods are herein considered: two recognized in the standards (the so-called 0/0 method and −1/+1 method) and a variation of the latter (−1/+1* method) used in Australia, Canada, France, and New Zealand. The 0/0 method considers neither fixation in the production stage nor releases of biogenic carbon at the end of a wood product's life. In contrast, the −1/+1 method accounts for the fixation of biogenic carbon in the production stage and its release in the end-of-life stage, irrespective of the disposal scenario (recycling, incineration or landfill). The −1/+1 method assumes that landfills offer only a temporary sequestration of carbon. In the −1/+1* variation, landfills and recycling are considered a partly permanent sequestration of biogenic carbon and thus fewer emissions are accounted for in the end-of-life stage. We examine the variability of the calculated life cycle-based greenhouse gas emissions calculated for a case study building by each participating country, within the same assessment method and across the methods. The results vary substantially. The main reasons for deviations are whether or not landfills and recycling are considered a partly permanent sequestration of biogenic carbon and a mismatch in the biogenic carbon balance. Our findings support the need for further research and to develop practical guidelines to harmonize life cycle assessment methods of buildings with bio-based materials. [Display omitted] • Life cycle assessments of the same multi-residential building were carried out by experts from 16 countries. • Effects of methods and datasets of biogenic carbon accounting in wood construction were identified. • Different end-of-life scenarios (incineration, landfill, recycling) cause variations in the results. • Different interpretations of the permanence of storing biogenic carbon in landfills also cause variations in the results. • The input and output flows of biogenic carbon must be balanced to correctly assess its climate change impacts. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is at the interface of biowaste management, energy generation, food production and land-based carbon dioxide removal. Strategic deployment of AD requires careful scoping of interactions with prospective alternative biowaste management, energy generation technologies and land uses to ensure effective delivery of climate neutrality and circularity. There remains a need to assess the greenhouse gas (GHG) mitigation efficacy of AD in the context of future alternative (counterfactual) processes associated with differential rates of decarbonisation across energy, waste management and land (including agriculture) sectors. To address this gap, prospective life cycle assessment (LCA) is applied to AD deployment scenarios across three decarbonisation contexts, using the UK as an example. Food waste prevention and diversion to animal feed always achieve more GHG mitigation than AD, even with sustainable intensification of food and feed production. Compared with maize- or grass-biomethane transport fuel, solar electricity generation can avoid 16 times more fossil energy and afforestation can mitigate six times more GHG per hectare of land occupied. Transport biomethane is currently the most effective biogas use for GHG mitigation, but large-scale combustion of biogas for electricity or industrial heat generation is the most effective long-term option as transport is electrified and bioenergy carbon capture & storage (BECCS) is deployed. Prioritising waste prevention and diversion to animal feed (including via insect meal) instead of maximising AD deployment could simultaneously: offset an additional 10–15% of national GHG emissions; meet an additional 2–4% of national energy demand; free enough arable land to provide 20–21% of national recommended protein and kcal intake. However, AD is likely to remain the best option to manage substantial volumes of residual food wastes and manures that will remain available even if ambitious projections on waste prevention and diet change are realised. [Display omitted] • Consequential LCA of anaerobic digestion (AD) in future decarbonisation contexts • GHG mitigation efficacy of AD declines as energy & transport systems decarbonise • AD-crop cultivation is a highly inefficient land use for energy generation and GHG mitigation • Carbon capture & storage could maintain effective mitigation from large-scale biogas use • Sustainable niche for waste-AD alongside waste prevention & diversion to animal feed [ABSTRACT FROM AUTHOR]