Biofuel production systems integration with green hydrogen (e.g., from proton exchange membrane electrolysers- PEM) can enable product yield improvements (e.g., gasification based biomethanol via hydrogenation of carbon-oxides) or co-production of synthetic methanol through hydrogenation of captured CO2. Environmental impact of these integrations compared to stand-alone systems is unknown. This study evaluates and compares the environmental performance of wood chip-based biofuel production systems, including advanced biocrude fuel (ABF), biomethanol (BMeOH), and biohydrogen (BH2), in stand-alone and integrated configurations with PEM-based hydrogen. The approach involved consequential life cycle analysis, focused on cradle-to-gate global warming potential (GWP), terrestrial acidification (TA), freshwater eutrophication (FE), and land use (LU) impacts. Gasification-based biomethanol yield enhancement with PEM hydrogen shows specific environmental benefits (e.g., in TA) while synthetic methanol co-production with ABF negatively impacts overall environmental performance. High electricity demand of PEM, influenced by the marginal electricity-mix, contributes to these trends. For biohydrogen, two-stage gasification route is preferable over pyrolysis-gasification due to higher biochar yield, which provide credit for replacing pulverized coal. Among the investigated systems, the stand-alone gasification-based biomethanol is the most environmentally efficient pathway for utilizing limited biomass. Meanwhile, the stand-alone two-stage gasification-based biohydrogen and stand-alone ABF show promise for decarbonizing hydrogen and diesel economies, respectively. All the biofuel systems outperform fossil fuels in GWP but lag in other categories (ABF- FE/LU, BMeOH- TA/FE/LU & BH2- TA/LU). The study emphasizes the importance of less resource-intensive green electricity supply and electrified logistics (e.g., biomass transport via freight trains) in enhancing the environmental performance of biofuel production systems.

Purpose: Global temperatures are expected to surpass the critical threshold of 1.5 °C above pre-industrial levels by 2040, necessitating the urgent need for large-scale and sustained carbon dioxide (CO<inf>2</inf>) removal. Tree-based systems offer a promising solution for carbon (C) sequestration and contribute to climate change mitigation. However, there is no consensus on accounting for biomass C sequestration in greenhouse gas (GHG) inventories, particularly in life cycle assessments (LCA). Although LCAs assess GHG emissions from production systems, integrating temporal changes in biomass C stocks remains a significant challenge. Methods: This study conducted a review to identify different methods for quantifying C sequestration and storage by trees in their biomass and to quantify the climate impact of this sequestered C for incorporation into LCA. Further, a case study on poplar trees was conducted to discuss these methods. Results and discussion: LCA practitioners can use several modeling approaches to quantify tree biomass C sequestration and storage, each with distinct strengths and limitations. These approaches include allometric, process-based, C-budget, and parametric models. This study found significant variability in the estimated biomass C sequestration and storage among these approaches, primarily due to the underlying methodological differences. Additionally, the variability in C sequestration and storage estimates increased with longer assessment durations. The results indicated that general allometric models may overestimate biomass C compared with species, climate, or site-specific models. However, when general models are adjusted for site-specific conditions and tree species, they provide more comparable estimates. This review identified nine impact assessment methods to quantify the climate change impacts of tree biomass C sequestration. The results showed that these impact assessment methods are time-sensitive, and the results may vary depending on the specific method and assessment duration chosen. Conclusions: This study concludes that, while simplified approaches to estimate biomass C sequestration and storage as well as impact assessment methods are useful, more detailed approaches may offer greater accuracy when detailed data are available. Therefore, in the future, methods for estimating biomass C sequestration and storage and its climatic impacts must strike a balance between complexity, simplification, and accuracy to improve their applicability and reduce uncertainties.

Bioenergy is a critical element in many national and international climate change mitigation efforts, including as a carbon dioxide removal strategy combined with the capture and durable geological storage of flue gas emissions (BECCS). However, divergent results on the effectiveness of bioenergy as a climate change mitigation measure are reported in the scientific literature. Climate impacts of bioenergy depend on case-specific factors, primarily biophysical features of the biomass production system, and the design and efficiency of conversion and capture processes. Estimates of climate impacts are also strongly affected by methodological choices and assumptions, and much of the divergence between studies derives from differences in the assumed alternate use of the land or feedstock, the alternate energy source and the system boundaries applied. We present a methodology to support robust estimates of the climate change effects of bioenergy systems, updating the standard methodology developed by the International Energy Agency's Technology Collaboration Program on Bioenergy. We provide guidance on the key choices including the reference land use and energy system that bioenergy is assumed to displace, spatial and temporal system boundaries, co-product handling, climate forcers considered, metrics applied and time horizon of impact assessment. Researchers should consider the whole bioenergy system including all life cycle stages, and choose system boundaries, reference systems and treatment of co-products that are consistent with the intended application of the results. The assessment should be normalised to a functional unit that can be compared with other systems delivering an equivalent quantity of the same function. All significant climate forcers should be included, and climate effects should be quantified using appropriate impact assessment methods that distinguish the impact of time. Consistency in methodology and interpretation will facilitate comparison between studies of different bioenergy systems.

In light of the environmental challenges currently facing humanity, the issue of the environmental sustainability of crop production is becoming increasingly pressing. This is due to the fact that global population growth and the related demand for food are placing significant pressure on the environment. Wheat is a strategic crop globally due to its extensive cultivation area, high production and consumption levels, and vital nutritional properties. It is cultivated across diverse climatic conditions and within various agricultural production systems. It is of the utmost importance to pursue sustainable wheat production on a global scale, given the necessity to protect the environment and climate. The application of life cycle assessment (LCA) enables the identification of potential avenues for enhancing wheat production processes, thereby reducing the negative environmental impacts associated with these processes. This paper presents a synthesis of the existing literature on the environmental LCA of wheat grain production. It compares the impacts of different production systems, highlights critical stages in wheat cultivation, and provides recommendations for sustainable practices and directions for future research.

Carbon dioxide removal (CDR) systems are an integral part of sustainable pathways limiting global warming to less than 2.0 °C. When the sole purpose of CDR is capturing and storing atmospheric CO2, carbon registries offer detailed procedures to calculate the carbon removal credits. However, the registries do not address how to distribute CO2 flows when CDR provides additional services. Standardized, transparent rules for distributing CO2 flows among CDR services are required for the formation of efficient private and public carbon markets. The lack of such rules could result in double counting if those reductions are allocated to more than one service, decreasing the trustworthiness of carbon removal credits or deterring the delivery of an additional low-carbon service, thus limiting the economic viability and deployment of CDR. We examine allocation rules in carbon registries and carbon accounting guidelines, including their life cycle assessment (LCA) principles. We evaluate physical (mass-based) and non-physical (economic) allocation methods using a generic CDR system and find both to be unworkable. We then develop a mass balance (MB) approach which can reliably allocate captured and stored carbon (CSC) between carbon removal credits and other services based on the value CO2 removal in those markets. This practical approach to allocation can be used in a transparent way to provide flexibility that would allow CDR services to capture the value of the multiple services they provide and, through this, promote the deployment of these sustainable alternatives.

This article provides guidelines for conducting consequential life cycle assessment (LCA) studies. It presents the main features of two alternative approaches used in LCA-attributional and consequential-and describes how consequential LCA can be performed consistently and appropriately, with an example provided to guide practitioners. It is argued that, despite its limitations, consequential LCA is a robust approach for estimating important indirect effects of products.

Context. Climate change and water scarcity are global challenges facing humanity. Animal agriculture generates considerable greenhouse gas (GHG) emissions and consumes large volumes of water from rivers, streams and lakes. Reducing consumption of animal agricultural products with a relatively high carbon or water footprint, such as dairy, is often promoted as a mechanism to reduce the environmental impacts of food production. Attributionally-based footprints do not, however, assess the consequences of a change in demand for a product. Aims. This study aimed to assess the water and climate change consequences of replacing NSW dairy production, and co-products of dairy production, with plant-based alternatives. Methods. Process-based consequential life cycle assessment was used. Key results. Water savings associated with the change would be limited and GHG emissions reductions would be ~86% of that as estimated by the carbon footprint of production. When NSW dairy production was replaced with soy-based alternatives and two GHG emissions reduction strategies were implemented across the industry, namely enteric methane inhibitors and flaring methane from effluent ponds, GHG emissions increased by 0.63 Mt carbon dioxide equivalent when dairy production was replaced. Conclusions. The environmental benefits associated with replacing NSW dairy production with plant-based alternatives should not be determined by attributionally-based approaches. Implications. Policies that aim to reduce the environmental impacts of agricultural production need to consider the market effects of a change in demand for products and not rely on estimated impacts of current production.

Purpose: Growing concern over climate change has increased interest in making use of the biosphere to reduce net greenhouse gas emissions by replacing fossil energy with bioenergy or increasing land-based carbon storage. An assessment of the effectiveness of these options requires detailed quantification of their climate-change mitigation potential, which must employ appropriate metrics to translate biophysical changes into climate-change impacts. However, the various currently available metrics use different proxy measures (e.g. radiative forcing, temperature changes, or others) as surrogates for climate-change impacts. Use of these different proxies can lead to contradictory conclusions on the most suitable policy options. We aim to provide criteria for the objective evaluation of metrics to build understanding of the significance of choice of metric and as a step towards building consensus on the most appropriate metric to use in different contexts. Methods: We compared fifteen available metrics that represent conceptual differences in the treatment of biospheric carbon fluxes and the proxies used to approximate climate-change impacts. We proposed a set of evaluation criteria related to the metrics’ relevance, comprehensiveness, ease of application and acceptance by the research and policy community. We then compared the different metrics against these criteria. Results and conclusions: The different metrics obtained scores from 10 to 21 (out of 30). The Climate-Change Impact Potential scored highest against the criteria, largely because it relates climate-change impacts to three different aspects of temperature changes; thus, it most comprehensively covers the different aspects of climate-change impacts. Therefore, according to our evaluation criteria, it would be the most suitable metric for assessing the effect of different policy options on marginal climate-change impacts. We demonstrated that the proposed evaluation criteria successfully differentiated between the fifteen metrics and could be used as a basis for selecting the most appropriate metric for specific applications.

The world's forests store large amounts of carbon (C), and growing forests can reduce atmospheric CO2 by storing C in their biomass. This has provided the impetus for world-wide tree planting initiatives to offset fossil-fuel emissions. However, forests interact with their environment in complex and multifaceted ways that must be considered for a balanced assessment of the value of planting trees. First, one needs to consider the potential reversibility of C sequestration in trees through either harvesting or tree death from natural factors. If carbon storage is only temporary, future temperatures will actually be higher than without tree plantings, but cumulative warming will be reduced, contributing both positively and negatively to future climate-change impacts. Alternatively, forests could be used for bioenergy or wood products to replace fossil-fuel use which would obviate the need to consider the possible reversibility of any benefits. Forests also affect the Earth's energy balance through either absorbing or reflecting incoming solar radiation. As forests generally absorb more incoming radiation than bare ground or grasslands, this constitutes an important warming effect that substantially reduces the benefit of C storage, especially in snow-covered regions. Forests also affect other local ecosystem services, such as conserving biodiversity, modifying water and nutrient cycles, and preventing erosion that could be either beneficial or harmful depending on specific circumstances. Considering all these factors, tree plantings may be beneficial or detrimental for mitigating climate-change impacts, but the range of possibilities makes generalisations difficult. Their net benefit depends on many factors that differ between specific circumstances. One can, therefore, neither uncritically endorse tree planting everywhere, nor condemn it as counter-productive. Our aim is to provide key information to enable appropriate assessments to be made under specific circumstances. We conclude our discussion by providing a step-by-step guide for assessing the merit of tree plantings under specific circumstances.