Open Access

Leftovers are particularly at risk of being discarded, and therefore a main component of household food waste. This study provides insights into sources of heterogeneity in leftover management behaviours, with a particular focus on the use of meal kits providing matched portion and ingredient sizes, and identifies consumer segments via a latent class analysis. We investigate whether belonging to a segment with positive attitudes toward leftovers, and engagement in conscious leftover management behaviours decreases the amounts of dinner leftovers and food waste. Besides, we demonstrate that several food waste antecedents, emotions, personal norms, intention and dinner procurement routines elicit leftover management segment membership. In addition to examining such individual differences, we also investigate the role of meal-level determinants, in particular, whether meal kits heterogeneously affect dinner leftovers depending on the consumer's leftover management segment. Data was collected from 868 households from six countries, using an online survey and diaries. Results of the latent class analysis point towards five consumer segments. We found differences in dinner leftovers amount across classes and detected heterogeneous effects of meal kits. That is, meal kits were able to diminish leftovers in two segments, but not in the other segments. These results provide novel insights into consumer heterogeneity regarding the occurrence, antecedents, and potential solutions of leftovers and resulting household food waste. Implications for both theory and policy are discussed.

The food system faces a multitude of challenges, including high greenhouse gas emissions, threats to biodiversity, increased diet-related diseases due to unbalanced diets, and socially problematic complex supply chains. This requires not only a transformation of the agricultural economy but also a change in the diet and lifestyles of all consumers. Developing and using digital and technological innovations can help to solve these challenges. In this context, the study provides impulses on how digitalisation can contribute to transforming production and consumption and which prerequisites have to be given to achieve this. The study describes the approaches for digitalisation along the value chain. These include optimising the use of resources in agriculture - for example with the help of smart farming - and supporting consumers with digital tools and assistance systems - such as apps designed to support grocery shopping. In addition, new business models and a better connection between production and consumption processes are also possible. This includes, for example, new digital sales channels or tracking and communicating sustainability indicators such as CO2 emissions across all steps of the value chain in order to enable all stakeholders to take reliable action.

To date, the circular economy has fallen short of its promise to reduce our resource demand and transform our production and consumption system. One key problem is the lack of understanding that highly promising strategies such as refuse, rethink, and reduce can be properly addressed using research on sufficiency. This article argues that a shift in focus is required in research and policy development from consumers who buy and handle circularly designed products to consumption patterns that follow the logic of sufficiency and explain how sufficiency-oriented concepts can be incorporated into existing social practices. The authors show that sufficiency is not necessarily as radical and unattractive as is often claimed, making it a suitable yet underrated strategy for sustainability and the transition to an effective circular economy. The case of urban gardening shows that small interventions can have far-reaching effects and transform consumption patterns as the logic of availability is contested by newly developed concepts of "enoughness" and opposition to "über-availability." The authors propose utilizing comprehensive state-of-the-art theories of consumption and human action when developing strategies and policies to make the circular economy sustainable while being more critical of utilitarian approaches. Using social practice theories that have proven to be beneficial allows human actions to be comprehensively analyzed by recognizing their embeddedness in social and material frameworks; addressing the meaning, competences, and materials of routinized human behavior; and examining indirect effects.

Public catering has become increasingly important in recent years. With increasing annual customers, the sector's impact on the environment is also growing continuously. At the same time, public catering offers a lever to promote sustainable nutrition that has rarely been used so far. Small changes in kitchen practices and food offers can thus be multiplied into a significant positive impact on environmental challenges, such as climate change or loss of biodiversity due to the large number of servings. In contrast to private households, management decisions in public catering can influence the food-related environmental impact of thousands of customers. This article deals with the nationwide level of greenhouse gas (GHG) emissions and resource use in the German public catering segment "business" and its saving potentials by different scenarios of unsupported and supported recipe revision. In this paper, we define "unsupported" as the intuitive optimization of recipes by employees of public catering businesses. In contrast, "supported" approaches had to meet specific target goals, for example of the Deutsche Gesellschaft für Ernährung; engl. German Nutrition Society or the sustainable level. Specifically, we will test how (A) an unsupported recipe revision, (B) a recipe revision based on dietary recommendations and (C) a recipe revision using scientific guidance affect the environmental impact of a dish. As a methodological framework, an online survey of public catering companies was conducted as well as a scenario analysis at menu level and at nationwide level. The results are based on empirical data on the one hand, and on extrapolations on the other. The results show that the nationwide implementation of recipe revision according to scientific guidance-such as concrete target goals for the GHG emissions per serving-can save up to 44% of resource use in the German business catering sector (which corresponds to 3.4 million tons of resources per year) and as much as 40% of GHG emissions (0.6 million tons GHG emissions per year). Even in the scenario of unsupported recipe revision, GHG and resource savings of up to 20% can be realized. The results show that public catering can reduce its material and carbon footprint by 20% overnight. Moreover, the findings show indications for the sustainable transformation of public catering. Nevertheless, it must be noted that these are some first steps of the transformation, which will require further changes with even greater impacts and political activities.

In material development processes, the question if a new alloy is more sustainable than the existing one becomes increasingly significant. Existing studies on metals and alloys show that their composition can make a difference regarding the environmental impact. In this case study, a recently developed air hardening forging steel is used to produce a U-bolt as an example component in automotive engineering. The production process is analyzed regarding the environmental performance and compared with the standard quench and tempering steels 42CrMo4 and 33MnCrB5-2. The analysis is based on results from applying the method of Life Cycle Assessment. First, the production process and the alterations on material, product, and process level are defined. The resulting process flows were quantified and attributed with the environmental impacts covering Carbon Footprint, Cumulative Energy Demand, and Material Footprint as they represent best the resource-, energy- and thus carbon-intensive steel industry. The results show that the development of the air hardening forging steel leads to a higher environmental impact compared to the reference alloys when the material level is considered. Otherwise, the new steel allows changes in manufacturing process, which is why an additional assessment on process level was conducted. It is seen that the air hardening forging steel has environmental savings as it enables skipping a heat treatment process. Superior material characteristics enable the application of lightweight design principles, which further increases the potential environmental savings. The present work shows that the question of the environmental impact does not end with analyzing the raw material only. Rather, the entire manufacturing process of a product must be considered. The case study also shows methodological questions regarding the specification of steel for alloying elements, processes in the metalworking industry and the data availability and quality in Life Cycle Assessment.

Urban transitions and transformations research fosters a dialogue between sustainability transitions theory an inter- and transdisciplinary research on urban change. As a field, urban transitions and transformations research encompasses plural analytical and conceptual perspectives. In doing so, this field opens up sustainability transitions research to new communities of practice in urban environments, including mayors, transnational municipal networks, and international organizations.

Household food waste is determined by a complex set of routinized behaviors, and disruption of these routines may allow for a decrease in this vast amount of food waste. The current study examines such a disruption of household routines: the meal box. The potential of meal boxes to diminish different types of household food waste is investigated for the first time, across different countries. After providing a framework comparing the effects of different types of meals on food waste, we subsequently examine the effects of subscription-based food supply (i.e., meal boxes) on total meal waste as well as on the different types of food waste: preparation, cooking, and plate waste. Our dataset contains 8747 meal observations from 955 households in six countries. Results from a Bayesian multilevel hurdle-lognormal model with random intercept show that, overall, meal boxes reduce total meal waste in comparison to traditionally cooked dinners (38% reduction). Meal boxes especially lower the occurrence and amount of pan-and-pot food that is wasted (i.e., cooking waste), and also lower the amount of meal preparation waste, yet lead to a higher occurrence of both preparation and plate waste compared to traditional meals. This shows how differences between meals affect household food waste, something that has received little prior research attention. Furthermore, whereas most prior research has focused on overall household food waste, our study illustrates that distinguishing between different types of household food waste can provide important new insights.

Food and nutrition systems are linked to all Sustainable Development Goals (SDGs), which makes their transition toward social-ecological behavior patterns crucial for an overarching sustainability transformation. The perspective of (urban) logistics is of special interest. It couples the production and consumption physically and virtually. In this context, we shed light on the design of the turnover point of food in urban areas from the supply chain toward consumers and contribute to an overarching systemic perspective toward establishing a sustainable multilevel food system. We describe current patterns in urban food systems and propose several principles for sustainable design of (urban) food systems based on concepts such as (regional) collaboration and food literacy. Using these principles, we provide four design scenarios that concretely imagine future urban food consumption and production patterns titled "slow stock supply service," "deliver into the daily walk," "central district food depot," "super food action place." With this work we provide a starting for reflecting whether certain combinations of principles actually lead to patterns of daily life that are feasible, acceptable, or desirable. Moreover, we provide an initial qualitative assessment to stimulate further research that explores scenario pathways and incorporates additional indicators regarding the impact on social-ecological. We open up various research questions with regard to the overarching question of how urban food logistics should be designed to be consistent with the SDGs.

Food production is responsible for approximately 17% of Germany's greenhouse gas (GHG) emissions. After retail, out-of-home catering is the second largest food sales channel in Germany. A variety of means on both the supply and demand side are necessary to stimulate, facilitate and encourage a more sustainable development and minimise GHG emissions in this sector. Nudges are one of these. This paper's focus lies on the demand side. Set in real-world laboratories, we use a standardised empirical approach to compare different nudging interventions belonging to the area of physical environment and consumers’ choice making process. We compare the effects of the same intervention across different settings and the effect of different, sequential nudging interventions in the same setting. Data was collected in eight workplace and school cafeterias in Germany over two project iterations (2016/2017; 2019/2020). A similar intervention design was applied. Comparability was assured by a harmonised menu. The first project iteration revealed that only one nudge (top menu position, +22.5%) led to significant increases in sustainable food choices, while results from the second iteration showed that all nudge interventions (best counter position, +11.6%; top menu position, +6,9%; label plus information, +15.9%) positively influenced consumer choice. Possible explanations such as the stricter compliance to the experimental design in the cafeterias but also societal developments such as the appearance of the Fridays for Future movement are discussed. As results vary between specific locations and settings, our findings suggest that nudges need to be adjusted to situational conditions for achieving highest efficacy.

To address climate change, the decarbonisation of Germany's existing building stock urgently needs to be prioritised. However, the rate and depth of refurbishment has lagged behind official targets for years. This is a particular problem in the rental sector, where the costs and benefits of energy efficiency measures tend to be unevenly distributed between landlords and tenants (the so-called "landlord-tenant dilemma"). Within the context of the current policy landscape, investments in energy efficiency consequently make most sense for landlords if the upfront costs can be refinanced via increased rental income or reduced vacant periods. This paper seeks to investigate the validity of this statement at city level by using a large dataset from one of Germany’s main internet property platforms to examine how the willingness of tenants to pay for energy efficiency varies across residential locations in the city of Wuppertal. The small-scale spatial analysis highlights the existence of a price premium for energy efficiency in the rental market for apartments; however, this premium is generally small (especially in comparison to other property enhancements, especially visible improvements) or even non-existent in some residential areas. Consequently, investing in energy efficiency is rarely an attractive option for landlords. Therefore, strong policy action, aligned with social and urban development policy objectives, is necessary to establish an effective incentive structure in the market and make investing in energy efficiency more attractive for both landlords and tenants.

Two thirds of today's world trade is based on global value chains and supply networks. Purely regional supply chains have become less important in recent decades. The effects of these globalised structures are manifold. On the one hand, they promote employment and generate prosperity. On the other hand, they are beset by extreme social, ecological and economic imbalances. The COVID-19 pandemic has demonstrated the fragility of existing supply chain systems. The lockdown continues to disrupt complex supply chains and many problems of existing production and consumption continue to worsen. COVID-19 is one example of the crises that can shake globally networked supply chains in the short term. Other crises, such as climate change, develop more insidiously and are less immediately recognisable. Different as they are, such crises have one thing in common: they highlight the vulnerability of global social and economic structures and illustrate the impact of global trade on the regions and people of the world. This is precisely where global sustainability strategy comes in - it aims to fundamentally reduce differences and inequalities in opportunities and quality of life. The COVID-19 pandemic has forced the entire world into upheaval, creating an opportunity to make sustainability a central political resilience strategy. In the wake of the Corona pandemic, the discussion about resilient communities has flared up. In order to guarantee supply in the face of such crises, these should be more strongly regional and circular in their economic approach and global and sustainable in their perspective. The aim should be sustainable, transparent, non-exploitative supply chains that guarantee the security of supply to cover basic needs and public services despite sudden changes and crises. This discussion paper draws a future scenario of globally cooperative, circular regional economies that fundamentally reduce global inequalities in opportunities and quality of life, while at the same time permanently preserving the natural foundations of life.

In Germany, the consumer sector "food" is responsible for around 15% of greenhouse gas emissions (GHG). Due to the high demand for food outside the home, changes in this area have the potential to significantly boost climate-efficient nutrition, and this includes changes in school kitchens. Currently, about 264 kg of GHG emissions per year are attributable to the food served to each school child who has school lunch year-round. Therefore, the project "Climate and Energy Efficient Cooking in Schools" ("Klima- und Energieeffiziente Küche in Schulen” or KEEKS for short) sought to determine the status quo in the kitchens of 22 all-day schools serving a total of 5,000 lunches per day. This was done by taking energy measurements and analyzing the equipment, technology and processes used in the kitchens, and by interviewing kitchen managers using guided interviews. Greenhouse gas emissions arising from menus and kitchen processes were calculated, potential savings were identified, and recommendations for action were developed and tested. The most effective measures - the reduction and substitution of meat and meat products and the establishment of efficient waste management systems - save around 10% of a school kitchen’s greenhouse gas emissions. The recommendations that have been developed can support kitchen staff in designing a climate-friendly, child-friendly, healthy and affordable menu in the school kitchen.

This paper presents an approach for assessing lifestyle carbon footprints and lifestyle change options aimed at achieving the 1.5 °C climate goal and facilitating the transition to decarbonized lifestyles through stakeholder participatory research. Using data on Finland and Japan it shows potential impacts of reducing carbon footprints through changes in lifestyles for around 30 options covering food, housing, and mobility domains, in comparison with the 2030 and 2050 per-capita targets (2.5-3.2 tCO2e by 2030; 0.7-1.4 tCO2e by 2050). It discusses research opportunities for expanding the footprint-based quantitative analysis to incorporate subnational analysis, living lab, and scenario development aiming at advancing sustainability science on the transition to decarbonized lifestyles.

For achieving a transition towards sustainable development, central importance is attached to science and education, and especially higher education. Suitable formats are needed for empowering students to perform transformative research. On the basis of transdisciplinary and transformative real-world laboratory research and futures studies, we develop encompassing learning and teaching module: the Transformative Innovation Lab (til). The lab builds on insights into five key competencies and three types of knowledge needed for developing socially robust sustainability innovations. In this paper, the main features of this experiential and reflexive format are presented and linked to a handbook for facilitating the lab. Central learnings for implementing the format in existing study programmes from two test runs at two German universities are shared and discussed.

Cross-country evidence on the adoption of energy-efficient retrofit measures (EERMs) in residential buildings is critical to supporting the development of national and pan-European policies aimed at fostering the energy performance upgrade of the building stock. In this light, the aim of this paper is to advance in the understanding of the probability of certain EERMs taking place in eight EU countries, according to a set of parameters, such as building typology, project types, and motivation behind the project. Using these parameters collected via a multi-country online survey, a set of discrete-choice (conditional logit) models are estimated on the probability of selecting a choice of any combination of 33 EERMs across the sampled countries. Results show that actions related to the building envelope are the most often-addressed across countries and single building elements or technology measures have a higher probability of being implemented. The modelling framework developed in this study contributes to the scientific community in three ways: (1) establishing an empirical relationship among EERMs and project (i.e., retrofit and deep retrofit), (2) identifying commonalities and differences across the selected countries, and (3) quantifying the probabilities and market shares of various EERMs.

Citizen science is a transdisciplinary approach that responds to the current science policy agenda: in terms of supporting open science, and by using a range of science communication instruments. In particular, it opens up scientific research processes by involving citizens at different phases; this also creates a range of opportunities for science communication to happen This article explores methodological and practical characteristics of citizen science as a form of science communication by examining three case studies that took different approaches to citizens' participation in science. Through these, it becomes clear that communication in citizen science is "always" science communication and an essential part of "doing science".

Digitalisation is disrupting business practices worldwide and transforming consumption patterns. While a global increase in wealth is leading to higher consumption rates, consumption-related decisions are increasingly based on digital information and marketing; furthermore, shopping increasingly takes place online and products and services are more and more digitalised. The transformative character of digitalisation calls for political action in order to ensure sustainable consumption in a new and dynamically changing context. Focusing on consumption is imperative in combatting many global challenges. Take climate change: consumption-based emissions (i.e. emissions from domestic final consumption and emissions caused by the production of imported goods) are rising more rapidly than production-based emissions in high-income countries. Meanwhile most political measures target production-based emissions (i.e. territorial emissions). The German council for sustainable development (Rat für Nachhaltige Entwicklung) has called for the §principle of sustainable development [to] serve as the political framework for digital transformation" as "digitalisation has the potential to engender disruptive developments in the business world as well as society as a whole that carry both great opportunities and significant risks". Thus, to implement the 2030 Agenda, in particular SDG 12, and the National Program Sustainable Consumption, it is key to seize the opportunities that digitalisation presents for sustainable consumption and tackle the challenges. This assessment report thus examines the following key question: "What are the implications of the digital transformation of consumption patterns for the implementation of the German sustainability strategy in, by and with Germany?"

To what extent can designers direct their professional practices towards serving the common good? Design constitutes itself anew with every project. Each project is both conditioned and made possible through a unique constellation of actors, timeframes, objectives, skills, etc. which arise from both social values and political agendas. We discuss the different approaches of two selected design projects by the authors, and the respective strategies and methods. While the designers' ambition in both projects was certainly to change an existing situation into a preferred one - the first by the means of interactive user engagement, the second through the idea of semi-finished product semantics - we emphasize on the challenges and ambiguities arising from the evolutionary process of design, aiming at the common good. Eventually we conclude that design processes can serve as a tool to debate rather than create the common good.

Agriculture is an economic sector with massive impact on biodiversity and agrobiodiversity. Sustainable diets represent a critical policy leverage and a realistic opportunity to reduce the environmental impact of the agro-food sector while improving human health at the same time. Eating out is an increasingly common habit for many consumers and, by offering sustainable dishes, catering companies can play a central role. To do this, they need to understand and correctly assess the sustainability of their food portfolio, but assessment tools are not well established yet. The NAHGAST project, of which this study was part, developed and tested a sustainability assessment tool for catering companies based on concrete targets defined per meal. This study addresses the lack of methods to evaluate the impact of food on biodiversity, with a particular focus on agrobiodiversity. The work illustrates a context-specific application of an enhanced DPSIR model to structure information and select indicators, and proposes a transdisciplinary use of existing metrics. Further research is needed in order to define scientifically sound target values or sustainability ranges for each indicator per meal, in order to calculate them. Strengths and limits of the study are discussed.

Since the middle of the 20th century, human society experiences a "Great Acceleration" manifesting in historically remarkable growth rates that create severe sustainability problems. The globally exploding potentials of information and knowledge exchange have been and are vital drivers for this acceleration. Society has now come to the point that it requires a "Great Transformation" towards sustainability to ensure the viability of the planet for a vital society. The energy transition plays a central role for this transformation. In this context, human society has developed a comparably good understanding of the necessary infrastructural changes of this transition. For transforming the patterns of energy production and use in an energy transition as part of the "Great Transformation", this process of change now needs to strengthen its focus on information, communication, and knowledge systems. Human society needs to establish a knowledge system that has the potential to create usable knowledge for sustainability solutions. This requires organizing a communication system that is sufficiently complex, interconnected, and, at the same time, efficient for integrating reflexive, open-ended, inter- and transdisciplinary learning, evaluation, and knowledge co-production processes across multiple levels. This challenge opens a wide field of research. This cumulative dissertation contributes to research in this direction by applying a systemic sustainability perspective on the content and organization of communication in the field of research on sustainable energy and the operational level of municipal climate action as part of the energy transition. Regarding sustainability, this thesis uses strong sustainability and its principles as a frame for evaluating the content of communication. Regarding the systemic perspective, the thesis particularly relies on the following theories: (i) the human-environment system model by R. Scholz as an overarching framework regarding interactions between humans and nature, (ii) social systems theory by N. Luhmann to reflect the complexity of society, (iii) knowledge management to consider the human character of knowledge and a practice-oriented perspective, and (iv) management cybernetics, in particular, the Viable System Model by S. Beer as a framework to analyze and assess organizational structures. Furthermore, the thesis leverages the potential of text mining as a method to identify and visualize patterns in texts that reflect prevalent paradigms in communication. The thesis applies the above conceptual and methodological basis in three case studies. Case Study 1 investigates the measures proposed in 16 municipal climate action plans of regional centers in Lower Saxony, Germany. It uses a text mining approach in the form of an Summary interpretation network analysis. It analyzes how different societal subsystems are connected at the semantic level and to what extent sustainability principles can be recognized. Case Study 2 analyzes and reflects paradigms and discursive network structures in international scientific publications on sustainable energy. The study investigates 26533 abstracts published from 1990 to 2016 using a text mining approach, in particular topic modeling via latent Dirichlet allocation. Case Study 3 turns again to the cases of municipal climate action in Lower Saxony examined in Case Study 1. It examines the involvement of climate action managers of these cities in multilevel knowledge processes. Using design principles for knowledge systems, it evaluates to what extent knowledge is managed in this field across levels for supporting the energy transition and to what extent local innovation potential is leveraged or supported. The three case studies show that international research on sustainable energy and municipal climate action in Germany provide promising contributions to achieve a transformation towards sustainability but do not fully reflect the complexity of society and still support a growth paradigm, in contrast to a holistic sustainability paradigm. Further, the case studies show that research and local action are actively engaging with the diversity of energy technologies but are lagging in dealing with the socio-epistemic (communication) system, especially with regard to achieving cohesion. Using the example of German municipalities, Case Studies 1 and 3 highlight the challenges of achieving coherent local action for sustainability and bottom-up organizational learning due to incomplete or uncoordinated multilevel knowledge exchange. At the same time, the studies also point out opportunities for supporting the required coherent multilevel learning processes based on local knowledge. This can be achieved, for instance, by strengthening the coordinating role of intermediary organizational units or establishing closer interactions between the local operational units and the national level. The thesis interprets and synthesizes the results of the three case studies from its systemic sustainability perspective. On this basis, it provides several generalized recommendations that should be followed for establishing viable communication systems, especially but not exclusively in policy-making: Systemic holism: Consider matter, energy, and information flows as an integrated triplet in the context of scales, structures, and time in the various subsystems. Knowledge society: Focus on the socio-epistemic (communication) system, e.g., using the perspective of knowledge systems and associated design principles considering, for instance, working environments across horizontal and vertical levels, knowledge forms and types, and knowledge processes. Sufficiency communication: Emphasize sufficiency approaches, make it attractive, and find differentiated ways for communicating them. Multilevel cohesion and innovation: Achieve cohesion between the local and higher levels and leverage local innovations while avoiding isolated local action. Organizational interface design: Define the role of organizational units by the interactions they create at the interfaces with and between societal subsystems. Local transdisciplinarity: Support local transdisciplinary approaches integrating various subsystems, especially industry, while coordinating these approaches from a higher level for leveraging local innovation. Digital public system: Exploit existing digital technologies or infrastructures in the public system and recognize the value of data in the public sphere for achieving cohesion. Beyond the above recommendations, this thesis suggests that potential for further research lies in: Advancing nature-inspired systemic frameworks. Understanding the structure and creation of human knowledge. Developing text mining methodologies towards solution-oriented approaches.

The transdisciplinary research mode has gained prominence in the research on and for sustainability transformations. Yet, solution-oriented research addressing complex sustainability problems has become complex itself, with new transdisciplinary research formats being developed and tested for this purpose. Application of new formats offers learning potentials from experience. To this end, we accompanied fourteen research projects conceptualized as real-world labs (RwLs) from 2015 to 2018. RwLs were part of a funding program on "Science for Sustainability" in the German federal state of Baden-Württemberg. Here, we combine conceptual and empirical work to a structured collection of experiences and provide a comprehensive account of RwLs. First, we outline characteristics of RwLs as transformation oriented, transdisciplinary research approach, using experiments, enabling learning and having a long-term orientation. Second, we outline eleven success factors and concrete design notes we gained through a survey of the 14 RwLs: (1) find the right balance between scientific and societal aims, (2) address the practitioners needs and restrictions, (3) make use of the experimentation concept, (4) actively communicate, (5) develop a "collaboration culture", (6) be attached to concrete sites, (7) create lasting impact and transferability, (8) plan for sufficient time and financial means, (9) adaptability, (10) research-based learning, and (11) recognize dependency on external actors. Characteristics and success factors are combined to illustrate practical challenges in RwLs. Third, we show which methods could be used to cope with challenges in RwLs. We conclude discussing the state of debate on RwLs and outline future avenues of research.

The earth's capacity to absorb greenhouse gases is ultimately a critical limiting factor in the handling of metals. The fact that the demand for metals far exceeds their secondary production is extremely problematic at this point. Nevertheless, metals are crucial for climate protection and energy system transformation. Examples are the rare earth metal neodymium used in high-performance permanent magnets in wind turbines, the alkali metal lithium as the most important component in batteries, or the metal tellurium used in thin-film solar cells to generate solar power. It is therefore essential to promote the aspects of resource efficiency and to strengthen the critical role of metals in national and European policy programs. Next to a global solution, a European solo effort with predominantly market-based instruments and the effects of committed behaviour by civil society in the European Union (EU), show that the EU can make a considerable contribution to sustainable development on its own. Thus, a comprehensive approach is needed for sustainable metal management in the sense of a circular economy on the European level fostering sustainable production and consumption pathways. But, this need and the special role of metals are not seen in the current debate about resources in society and politics. Due to the fact that in public perception, metallic raw materials are often discussed as less urgent than energy or polymer raw materials, this article aims to highlight the critical role of metals. Further, the objective of this contribution is to show which prerequisites exist for the development and establishment of a holistic metal management and where political strategies have to start. Challenges needed to be overcome to achieve such a holistic metal strategy and management are highlighted. In particular, the role of the metal industry, circular product design and labelling and corresponding indicator systems is examined. In addition, the special role of digitalisation is being worked out. Finally, conclusions are drawn and shown which aspects have to be considered for a holistic metal strategy and management.

Recent research on the natural resource use of private consumption suggests a sustainable Material Footprint of 8 tons per capita by 2050 in industrialised countries. We analyse the Material Footprint in Germany from 2015 to 2020 in order to test whether the Material Footprint decreases accordingly. We studied the Material Footprint of 113,559 users of an online footprint calculator and predicted the Material Footprint by seasonally decomposed autoregressive (STL-ARIMA) and exponential smoothing (STL-ETS) algorithms. We find a relatively stable Material Footprint for private consumption. The overall Material Footprint decreased by 0.4% per year between 2015 and 2020 on average. The predictions do not suggest that the Material Footprint of private consumption follows the reduction path of 3.3% per year that will lead to the sustainable consumption of natural resource

Financial institutions play a crucial role in achieving the 2015 Paris Climate Agreement. They can manage capital flows for financing the required transformation towards a decarbonized industry. Currently established policy programs and regulations at European and national level increasingly address financial institutions to make their climate warming impact measurable and transparent. However, required science-based assessment methods have not been sufficiently developed so far. This paper discusses methodological opportunities and challenges for measuring carbon footprints of financial institutions. Based on a scientific case study undertaken with the German GLS Bank, the authors introduce an innovative method for quantifying greenhouse gas emissions from a bank's asset with a focus on loans. The authors apply an input/output database to calculate greenhouse gas (GHG) intensities and allocate them with bank's loans and investments. Moreover, the paper provides insights of calculating avoided GHG emissions initiated by a bank's investment and loans. In conclusion, a high degree of consistent and standardized assessment methods and guidelines need to be developed and applied to promote comparability and transparency.

Many technical solutions have been developed to enhance the energy efficiency in buildings. However, the actual effectiveness and sustainability of these solutions often do not correspond to expectations because of the missing perspective of design, user's real needs, and unconsidered negative side effects of their use (rebounds). With the aim to help address these challenges, this paper presents results of a longitudinal living lab study and proposes a user-centered building management system (UC-BMS) as a prototype for office buildings. Based on mixed methods, UC-BMS was co-developed, tested, and evaluated in Germany in up to six office buildings, 85 offices, and within two heating periods. The results demonstrate that such user-oriented approach can save up to 20% of energy while maintaining or even improving comfort and work productivity. The findings show three main areas of intervention and elements of UC-BMS: (1) How interactive design and feedback systems (e.g., air quality) can stimulate ventilation practices and energy efficiency in offices and (2) supporting heating system optimization e.g., by better understanding office behavior. (3) Finally, an office comfort survey was conducted to enable communication between facility management and office users and thus limiting complaints and adapting the heating system towards actual office user needs.

There is urgent need to change the way we make use of non-renewable resources, especially metals, to sustain their availability for vital technologies associated with achieving change towards sustainability, but also to minimize negative impacts and to achieve a fair distribution of the wealth and burdens associated with their production and use. Especially public actors (state governments and administrations) have recently formulated strategies as a means to guide action fostering these goals. Yet, these strategies are very different in their character, which makes it difficult to compare them and learn how to best design strategies for a given context to contribute to the necessary change. To approach this question, we analyzed 37 national mineral resource-related strategy documents worldwide concerning their contextual conditions, motivation, and objectives. Following the general inputs for transition strategies (current and target state, transition strategy), we identified four clusters of strategy documents that share similarities in their approaches and support the development of specific recommendations for future strategy design in terms of both content and process. Designing strategies with a clear structure that interlinks a systems-based description of the current state, a clear vision (oriented at sustainability principles) and a sufficiently differentiated but at the same time flexible transition pathway improves their potential to contribute to more sustainable metal production and use.

With regard to residential energy use in the European Union (EU), most studies consider potential adopters of the technology (e.g., private owners) as being the sole decision-makers in the technology selection. However, during an integrated decision-making process (e.g., a construction project) multiple stakeholders will interact, influencing each other's judgement, thereby making it difficult to discern who is affecting the final decision, and to what extent. The goal of this study is to outline the full network of stakeholders involved in the decision-making process, along with their degree of power and interaction in the technology choice. For this purpose, empirical evidence from a multi-country survey is examined using social network analysis (SNA). The information is compared across building typologies, project types and countries (i.e., Italy, Spain, Germany, Poland, the United Kingdom, France, Belgium and the Netherlands). The results demonstrate that, in EU residential buildings, potential adopters of the technology are not the only stakeholders involved in the technology selection. They are in all instances in communication with multiple stakeholders, some of whom also hold a high level of power in the decision (i.e., key persuaders). Furthermore, their level of power and communication varies substantially across building typologies, project types and countries.

Addressing the prevailing mode of high-carbon lifestyles is crucial for the transition towards a net-zero carbon society. Existing studies fail to fully investigate the underlining factors of unsustainable lifestyles beyond individual determinants nor consider the gaps between current footprints and reduction targets. This study examines latent lifestyle factors related to carbon footprints and analyzes gaps between decarbonization targets and current lifestyles of major consumer segments through exploratory factor analysis and cluster analysis. As a case study on Japanese households, it estimates carbon footprints of over 47,000 households using expenditure survey microdata, and identifies high-carbon lifestyle factors and consumer segments by multivariate regression analysis, factor analysis, and cluster analysis. Income, savings, family composition, house size and type, ownership of durables and automobiles, and work style were confirmed as determinants of high-footprint Japanese households, with eight lifestyles factors, including long-distance leisure, materialistic consumption, and meat-rich diets, identified as the main contributory factors. The study revealed a five-fold difference between lowest and highest footprint segments, with all segments overshooting the 2030 and 2050 decarbonization targets. The findings imply the urgent need for policies tailored to diverse consumer segments and to address the underlying causes of high-carbon lifestyles especially of high-carbon segments.

The Wuppertal Institute conducted an impact analysis of the NRW sustainability bond #5 of 2019 on behalf of the State government of North Rhine-Westphalia (NRW). The most recent bond has a volume of EUR 2.25 bn, a term of 15 years and consists of 52 eligible projects from the State's 2018 general budget (sustainable value-added was confirmed in a second party opinion by ISS-oekom). This report analyses the contribution of the bond to climate mitigation, sustainable land use and social impacts. It also includes information on the impacts of the previous four bonds (NRW sustainability bond #1 to #4).

Responsible consumption and production is one of the Sustainable Development Goals of the United Nations. To achieve this goal the currently high extraction rates of natural resources, that our economy is based on, needs a transformation of the consumption and production system considering technological as well as social change. One of the promising transition approaches is seen in collaborative consumption with its many facets of socio-cultural innovations and fast growing number of participants and businesses. With a decreasing production of goods, due to a utilisation of underutilised assets, these offers might support an absolute reduction of the global resource use. However, a positive environmental effect depends on the setting and the social practices of such sharing offers and is not sustainable or resource efficient generally. Also, resource efficient practices with a low diffusion potential that stick in a niche offer no leverage to achieve sustainable consumption patterns. Thus, this paper describes a mixed method approach to analyse the resource efficiency and diffusion potential of 20 sharing offers in the area of mobility, housing & travel and everyday objects in Germany. Results show that the overall positive environmental connotation of sharing offers cannot be confirmed. We identified five clusters of offers that are all treated to be differently when it comes to deploying the positive potential and avoid unnecessary societal effort to achieve the mentioned Sustainable Development Goal.

To contribute to a better understanding of consumer food leftovers and to facilitate their reduction in out-of-home settings, our study analyzes the effects of two common intervention strategies for reducing leftovers in a holistic behavioral model. Based on a quasi-experimental baseline-intervention design, we analyzed how the display of information posters and the reduction of portion sizes take an effect on personal, social and environmental determinants in a structural equation model. Applying data from online surveys and observations among 880 guests (503 baseline, 377 intervention) during two weeks in a university canteen, the suggested model allows to assign effects from the two interventions on plate leftovers to specific changes in behavioral determinants. Portion size reductions for target dishes are found to relate to lower levels of plate waste based on conscious perception, represented in smaller portion size ratings. Effects from seeing information posters are found to base on changed personal attitudes, subjective norms and perceived behavioral control. However, depending on how an individual reacts to the information (by only making an effort to finish all food or by making an effort and additionally choosing a different dish in the canteen) there are opposite effects on these determinants and consequently also on plate leftovers. Overall, the differentiated results on intervention effects strongly support the benefits of more holistic and in-depth analyses of interventions to reduce plate leftovers and therefore to contribute to more sustainable food consumption in out-of-home settings.

Improvements in energy efficiency have numerous impacts additional to energy and greenhouse gas savings. This paper presents key findings and policy recommendations of the COMBI project ("Calculating and Operationalising the Multiple Benefits of Energy Efficiency in Europe"). This project aimed at quantifying the energy and non-energy impacts that a realisation of the EU energy efficiency potential would have in 2030. It covered the most relevant technical energy efficiency improvement actions in buildings, transport and industry. Quantified impacts include reduced air pollution (and its effects on human health, eco-systems), improved social welfare (health, productivity), saved biotic and abiotic resources, effects on the energy system and energy security, and the economy (employment, GDP, public budgets and energy/EU-ETS prices). The paper shows that a more ambitious energy efficiency policy in Europe would lead to substantial impacts: overall, in 2030 alone, monetized multiple impacts (MI) would amount to 61 bn Euros per year in 2030, i.e. corresponding to approx. 50% of energy cost savings (131 bn Euros). Consequently, the conservative CBA approach of COMBI yields that including MI quantifications to energy efficiency impact assessments would increase the benefit side by at least 50-70%. As this analysis excludes numerous impacts that could either not be quantified or monetized or where any double-counting potential exists, actual benefits may be much larger. Based on these findings, the paper formulates several recommendations for EU policy making: (1) the inclusion of MI into the assessment of policy instruments and scenarios, (2) the need of reliable MI quantifications for policy design and target setting, (3) the use of MI for encouraging inter-departmental and cross-sectoral cooperation in policy making to pursue common goals, and (4) the importance of MI evaluations for their communication and promotion to decision-makers, stakeholders, investors and the general public.

Green Information Systems in general, and footprint calculators in particular, are promising feedback tools to assist people in adopting sustainable behaviour. Therefore, a Material Footprint model for use in an online footprint calculator was developed by identifying the most important predictors of the Material Footprint of the calculator's users. By means of statistical learning, the analysis revealed that 22 of the 95 predictors identified accounted for 74% of the variance in Material Footprints. Ten predictors out of the 95, mainly from the mobility domain, were capable of showing a prediction accuracy of 61%. The authors conclude that 22 predictors from the areas of mobility, housing and nutrition, as well as sociodemographic information, accurately predict a person's Material Footprint. The short and concise Material Footprint model may help developers and researchers to enhance their information systems with additional items while ensuring the data quality of such applications.

This thesis justifies and develops a sustainable level of Lifestyle Material Footprint (LMF) as a benchmark for designing sustainable lifestyles. It shows the application of the benchmark in a Household-level Sustainability Transition method and presents a framework for inspiring design solutions towards a Design for One Planet (Df1P). The thesis shows how the Material Input per unit of Service (MIPS) concept has developed from product orientation to the application to household consumption and from technically-focused measurement into an integral part of methods for designing one-planet lifestyles and supporting solutions. This provides both an advanced application of the concept and its opening to new purposes and users. The core of the thesis is the suggestion of a sustainable material footprint benchmark of 8 tonnes per person per year as a resource cap target for household consumption in Finland, an 80% (factor 5) reduction from present average. The 8 tonnes benchmark opens the possibility for a target-oriented, planned reduction of LMFs by target-setting, experimenting and up-scaling of sustainable solutions. The method enabled the participating households to perform footprint reductions of 26–54% during the one-month experiment phase. Notable footprint reductions are thus possible even in the short term, which is an important message to other households and other actors in society. Calculating households' LMFs makes visible the structures underlying household consumption and the need for change not only in household consumption but also in the supply of products, services and infrastructure, and thus systemic changes initiated by others than households. The orientation framework of Df1P suggests measures that could be promoted by means of design, and structures them in a matrix incorporating priority action areas in the fields of housing, nutrition and mobility, and the domains of product design, service design, infrastructure planning and communication design. Mainstreaming sustainable lifestyles will potentially require a new design culture, but at least significant efforts in product design, service design and infrastructure planning as well as in making sustainable solutions attractive to consumers and disrupting existing routines. The more technology and infrastructure can be integrated into this change, the more space will be left for individual diversity in achieving sustainable household consumption. The orientation framework could provide a first step towards Df1P practice by inspiring designers to integrate the recognition of the planetary boundaries into their work.

Background: For a successful transition to a sustainable energy system, not only technical but also social innovations are required. A major challenge to social innovation research is how to translate the social innovation from a novelty with big potential into a mainstream practice. The multilevel perspective (MLP) of socio-technical transitions provides a heuristic to understand how niches can potentially break through to the regime level. In this paper, we examine in how far a multilevel perspective approach is suited to analyze and better understand diffusion trajectories of social rather than technological innovations, taking a social practice theory perspective. Five example projects, selected among the top social innovations for the Energiewende in North Rhine-Westphalia, are analyzed. We discuss to what extend the MLP provides a helpful tool to understand the transition processes. Results: Social innovations can be very divers. We find that the MLP does not offer a one-size-fits-all framework for the analysis of the diffusion of social innovations. The MLP proves applicable only in those cases where the social innovation (1) can lead to a system change and (2) has a clear competing or symbiotic relationship with an existing regime. Conclusions: Social innovations that aim to be transformative in the sense that they have the goal to be system changing (rather than incremental) can be analyzed along the heuristics of the MLP. For this type of social innovation, the MLP can be fruitful to learn to better understand the diffusion dynamics of social innovation and the barriers and drivers they might face. However, for social innovations that aim at incremental improvements without challenging the existing system, the MLP cannot be applied to study the diffusion process.

Real-world laboratories (RwLs, German Reallabore) belong to a family of increasingly popular experimental and transdisciplinary research approaches at the science-society interface. As these approaches in general, and RwLs in particular, often lack clear definitions of key characteristics and their operationalization, we make two contributions in this article. First, we identify five core characteristics of RwLs: contribution to transformation, experimental methods, transdisciplinary research mode, scalability and transferability of results, as well as scientific and societal learning and reflexivity. Second, we compare RwLs to similar research approaches according to the five characteristics. In this way, we provide an orientation on experimental and transdisciplinary research for societal transformations, and reveal the contributions of this type of research in supporting societal change. Our findings enable learning across the different approaches and highlight their complementarities, with a particular focus on RwLs.

We present the results of a regression analysis of a large-scale integrated user online application that surveys natural resource use and subjective well-being in Germany. We analyse more than 44,000 users who provided information on their natural resource consumption (material footprint) as well as their personal socio-economic and socio-psychological characteristics. We determine an average material footprint of 26 tonnes per person per year. In addition, we endeavour to determine how much environment humans need by regressing natural resource use as well as relevant socio-economic and socio-psychological features on subjective well-being. We establish a slightly negative correlation between subjective well-being and material footprints. A higher material footprint is associated with lower subjective well-being. We conclude that consumer policies seeking to promote sustainable behaviour should highlight the fact that a lower material footprint may result in greater subjective well-being.

Sustainable out-of-home nutrition can help achieve overarching sustainability goals through a transformation in demands of consumers in this growing market. Studies indicate that individual food choice behaviours in out-of-home settings relate to a wide set of personal, social and situational factors. These factors can be influenced by various intervention strategies. In an expert meeting and a focus group we invited caterers and consumers to generate, discuss and evaluate various practical intervention ideas. Both parties largely perceive the explored ideas as useful and agree on key intervention ideas. Overall caterers and consumers state to prefer nudging strategies over information and participation interventions.

The field of nutrition will face numerous challenges in coming decades; these arise from global consumption patterns and lead to a high use of resources. Actors in the catering sector face difficulties in promoting their solutions for a more sustainable situation in their field, one of them being the lack of acceptance from consumers. We must ask the question of how to influence consumer behavior and bring forth a transition towards more sustainable food consumption. This paper presents results of a qualitative assessment of eating practices. A group of ten consumers participated in problem-centered interviews and provided data on their eating-out behavior over the course of two weeks. Using the theoretical approach of practice theory, the data gathered in this study were used to form an understanding of the practice of eating out with a focus on the daily routines that influence consumer choices. The results indicate that the practice of eating out is highly dependent on external factors. Busy lifestyles, mobility routines and a perceived lack of time prompt the decision to eat out. Consumers consciously do so to save time and effort and to streamline their schedules. Mobility seems to be an important driver for eating out. Participants try to limit the ways they undertake eating out yet often stop for a meal in-between appointments spontaneously. Findings suggest that nutrition knowledge and sustainable mindsets have little influence on the eating decisions away from home: Participants show a high level of distrust towards quality claims and put their health concerns aside eating out. We can conclude that the act of eating out is strongly influenced by daily routines and those practices that precede or succeed it. Changes in work and mobility patterns are very likely to have an impact on the way consumers eat away from home.