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Background Human and earth system modeling, traditionally centered on the interplay between the energy system and the atmosphere, are facing a paradigm shift. The Intergovernmental Panel on Climate Change’s mandate for comprehensive, cross-sectoral climate action emphasizes avoiding the vulnerabilities of narrow sectoral approaches. Our study explores the circular bioeconomy, highlighting the intricate interconnections among agriculture, forestry, aquaculture, technological advancements, and ecological recycling. Collectively, these sectors play a pivotal role in supplying essential resources to meet the food, material, and energy needs of a growing global population. We pose the pertinent question of what it takes to integrate these multifaceted sectors into a new era of holistic systems thinking and planning. Results The foundation for discussion is provided by a novel graphical representation encompassing statistical data on food, materials, energy flows, and circularity. This representation aids in constructing an inventory of technological advancements and climate actions that have the potential to significantly reshape the structure and scale of the economic metabolism in the coming decades. In this context, the three dominant mega-trends—population dynamics, economic developments, and the climate crisis—compel us to address the potential consequences of the identified actions, all of which fall under the four categories of substitution, efficiency, sufficiency, and reliability measures. Substitution and efficiency measures currently dominate systems modeling. Including novel bio-based processes and circularity aspects might require only expanded system boundaries. Conversely, paradigm shifts in systems engineering are expected to center on sufficiency and reliability actions. Effectively assessing the impact of sufficiency measures will necessitate substantial progress in inter- and transdisciplinary collaboration, primarily due to their non-technological nature. In addition, placing emphasis on modeling the reliability and resilience of transformation pathways represents a distinct and emerging frontier that highlights the significance of an integrated network of networks. Conclusions Existing and emerging circular bioeconomy practices can serve as prime examples of system integration. These practices facilitate the interconnection of complex biomass supply chain networks with other networks encompassing feedstock-independent renewable power, hydrogen, CO 2 , water, and other biotic, abiotic, and intangible resources. Elevating the prominence of these connectors will empower policymakers to steer the amplification of synergies and mitigation of tradeoffs among systems, sectors, and goals.

Background This paper aims to analyze, synthesize and evaluate the main differences, similarities, advantages, and disadvantages of the narratives of green economy (GE), circular economy (CE) and bioeconomy (BE) models within a sustainability framework. The article seeks to provide a critical comparison of the notion of three models, related in their concepts, approaches and tools, as well as establish and analyze the strategies that lead to a change in the dominant paradigms in sustainability applications. Main text The emerging green, circular and bioeconomy approaches focus on proposing strategies that lead to sustainability. This study shows that despite their notable conceptual differences, a model that adapts to rapid changes in the needs and limitations of natural resources is common across all approaches. However, in terms of analysis and application, they are not always clear because of the complexity of differentiating approaches, conceptual incorporation frameworks and analytical tools. The results show that, in the environmental dimension, the circular economy and bioeconomy focus on resource management, whereas the green economy starts by analyzing ecological processes to reduce environmental risk and ecological scarcity. In the economic dimension, the circular economy aims to decouple economic growth from environmental pressure, whereas the bioeconomy emphasizes the processing and enhancement of biological raw materials to foster new value chains. Conclusions The findings of this paper clarify the limits, synergies, and differences in sustainability between the concepts of the green economy (GE), the circular economy (CE) and the bioeconomy (BE), and address gaps in the literature. These concepts continue to be limited by their economic growth; limits in the interrelation between the biosphere and individuals; and specific assessments of the environmental, social, and economic aspects of sustainable management. Key Points Green and circular economy analyzes and proposes actions that balance the behavior of society and the environment. The bioeconomy could reach limits of unsustainability by managing biological resources as infinite. Green, circular and bioeconomy do not concisely address a methodology to achieve sustainability. Green, circular and bioeconomy propose viable but insufficient strategies for economic, environmental, and social aspects.

Background Global warming and the increasing risk of natural disasters force us all to act. As the reduction of carbon dioxide (CO 2 ) emissions has been proven effective but insufficient on its own, Carbon Capture and Utilization (CCU) technologies emerged to fill the gap. Using CCU technologies, CO 2 is captured and further processed into valuable products instead of being emitted into the atmosphere. Method This study investigates the prevailing public perception of such CCU-based products by the example of clothing and cosmetics. We applied the method of conjoint measurement to experimentally examine context-related factors (= attributes) in different usage settings and explored the consumers’ decision profiles for or against the usage of CCU-based products (cosmetics and clothing). Conjoint measurements were realized as an online experiment, addressing acceptance patterns and preferences in four European countries (Germany, Norway, Spain, and Poland). In addition, we assessed general attitudes and affective assessments of the CCU products. A total of N  = 828 participants took part in the study, and the international subsamples were comparable. Results Results revealed that health compatibility is the main adoption-driving factor in the decisions for or against the use of the products. Still, attributes like the environmental impact, product quality, and information flow play an important role as well, even though to a lesser extent. Participants from different countries significantly differ in their cognitive and affective evaluations of acceptance-related attributes. Conclusions The outcome provides insights into differences in Pan-European comparison and helps to understand the public motives and country-specific terms of use for CCU-based products, effectively establishing recommendations for policy and governance.

Background The circular economy represents a vision of ever-increasing importance for policy making. In this paper, the circularity of transportation fuel production systems is explored, as energy carriers are seldom the focus of existing methods. A theoretical framework for understanding the circularity of energy carriers was devised based on the renewability and secondary fractions of inputs and the recycling of outputs, which cover both biological and technical cycles. Based on this framework, and with input from actors working in the field of transport fuels, a six-step method was developed to assess the circularity of energy carriers. The method uses a life cycle perspective for assessing energy carriers across their life cycle. Results This method was applied to four production systems in the Swedish context: hydrogenated vegetable oil (HVO) from tall oil, ethanol from forest residues, biomethane from household food waste, and battery–electric mobility. The results showed that all studied biofuels have a high degree of circularity due to the use of secondary materials as a feedstock. The biomethane system scored the highest percentage, with a circularity score of 81%, while the HVO and ethanol systems only reached a score of 75% and 45%, respectively. The battery–electric system, on the other hand, performed worse at only 17% circularity due to the low degree of circularity in the battery production. One “greening” scenario was tested for each production system to explore the impact of possible future improvements. Conclusions The results showed that second-generation biofuels align well with the circular economy concept as they upcycle low-value resources into high-value products. At the same time, electric mobility requires a higher degree of material recirculation to further align it with the circular economy. Furthermore, all production systems indicated improvement potentials and should, therefore, be aimed at increasing their recirculation rates and use of renewable resources. In conclusion, this article gives valuable input into the broader decision process to determine which fuels should be promoted during the transition away from fossil fuels, as circularity is one aspect to be considered.