Klimaschutz, Ressourcenschonung und Circular Economy als Einheit denken

Der European Green Deal steht faktisch auf zwei Säulen: Um die Netto-Emissionen von Treibhausgasen (THG) bis 2050 auf Null zu reduzieren, ist eine Transformation erforderlich, die insbesondere die Energiewirtschaft, aber auch alle anderen emissionsrelevanten Sektoren betrifft. Daneben steht die Circular Economy, die den Druck auf die natürlichen Ressourcen reduzieren und ein nachhaltiges Wachstum ermöglichen soll. Dabei geht es um den schonenden Umgang mit Materialien, vor allem durch Recycling, aber auch durch andere Formen der nachhaltigeren Nutzung von Materialien wie Reuse, Repair, Refurbishing oder alternativen Geschäftsmodellen. Im Fokus steht also immer wieder der Umgang mit Energie und Materialien. Bislang werden diese Bereiche meistens separat behandelt: der Klimaschutz und die Energiewende auf der einen Seite und die Ressourceneffizienz und -schonung auf der anderen. Doch beide Themen sind unmittelbar miteinander verbunden: Der Umbau der Energiewirtschaft und der Ausbau der regenerativen Energien wird zwar den Einsatz von fossilen Energieträgern deutlich reduzieren und damit auch die Treibhausgasemissionen, allerdings werden dafür Erzeugungstechnologien und Infrastrukturen benötigt, die große Mengen an Materialien benötigen, darunter auch viele sogenannte kritische Materialien. Gerade der Wechsel von fossilen zu regenerativen Energie-

Wie kann der Wärmebedarf von Gebäuden in Kommunen simuliert werden, der mögliche Einsatz von zentralen und dezentralen Versorgungssystemen geprüft und die lokalen Entscheidungsträger dabei unterstützt werden? Diese Fragen behandelt Verena Weiler in ihrer Arbeit (Weiler und Eicker 2021 Thinking of climate protection, resources conservation and the circular economy as a unit The European Green Deal is in fact based on two main principles: In order to reduce the net emissions of greenhouse gases (GHG) to zero by 2050, a transformation is required which particularly affects the energy industry, but also all other emission-relevant sectors. In addition, there is the Circular Economy, which aims to reduce pressure on natural resources and enable sustainable growth. This involves the careful use of materials, primarily through recycling, but also through other forms of more sustainable use of materials such as reuse, repair, refurbishing or alternative business models.
The focus is always on the use of energy and materials. Until now, these areas have mostly been treated separately: Climate protection and energy transition on the one hand, resource efficiency and conservation on the other. But the two topics are directly linked: The restructuring of the energy industry and the expansion of renewable energies will significantly reduce the use of fossil fuels and thus also GHG emissions. However, this requires production technologies and infrastructures that need large quantities of materials, including many so-called critical materials. The change from fossil to renewable energy technologies requires an increased use of materials, since the energy density of renewable sources is significantly lower than that of fossil energy sources and the energy has to be collected in a virtually material-intensive way. The supply of materials is not possible without the use of energy. Here, there is a direct feedback between energy and materials.
The circular economy also does not work without energy, and so far,-and probably for many decades to come-not without GHG emissions. The circular economy can make a significant contribution to climate protection because recycling materials is often more energy-efficient than extracting new materials from mines. But there are also limits where recycling no longer makes sense, for example, when the dissipation of important substances in the technosphere is too high and the collection and separation simply becomes too complex. The lower the concentration of the substances in the waste, the greater the energy required for recycling and thus also the associated GHG emissions.
These aspects have been known to experts for a long time, even though they hardly play a role in public and political discussions. However, it is particularly problematic that the political control systems hardly consider such interactions between the energy and the material issue. This will be explained by an example.
Since the Kyoto resolutions and the follow-up conferences, national climate protection policy has been geared towards the reduction of the respective national GHG emissions, i.e. each nation attempts to reduce emissions on its territory. This makes sense and, accordingly, an extensive monitoring and accounting system on GHG emissions has been established in recent decades. In Germany, for example, GHG emissions are balanced every year and the reduction plans, especially in the energy policy, are aligned accordingly. In 2016, approximately 900 million tons of CO2 equivalent were released (Umweltbundesamt 2021).
But these balances are only half the truth (see Fig. 1). If we calculate what Germany causes in terms of GHG emissions, then those emissions must also be included in the supply chain that result from the provision of raw materials and goods in other countries, which amounted to an additional 820 million tons of CO2 equivalent  in 2016. Germany is partly responsible for this, through domestic consumption and investment, through the production of goods, some of which are passed on again for export. Until now, the argumentation has mostly been that the climate backpack of imported goods equalizes the climate backpack of exported goods. This is what the figures of the Federal Statistical Office have suggested so far (Destatis 2019). But new calculations show that the climate backpack of imported goods to Germany is much larger than previously assumed ). This imbalance of "embodied emissions" of import and export goods also applies to Europe as a whole, as studies on global economic interdependencies and emissions show (Wood et al. 2019).
Thus, while energy policy is particularly focused on territorial emissions balances, resource policy must look at the entire supply chain-from the mine to the product manufacturing and use phase to disposal or recycling. Many of Abb. 2 Die THG-Emission (in Mio. t/a) von den mengenmäßig wichtigsten 12 Chemikalien, die in Deutschland derzeit produziert werden, und die potenziellen THG-Emissionen, wenn sie in China bzw. den USA produziert würden Fig. 2 The GHG emissions (in million t/a) of the 12 most important chemicals currently produced in Germany and the potential GHG emissions if they were produced in China or the USA the environmental and social impacts that arise are shared across the world. They can only be measured sensibly with life cycle approaches. The methodological tools for this have been created in recent decades in the form of life cycle assessment or the carbon footprint and have also been standardized internationally as ISO standards.
One might think that this would not be a problem for specific policy, since one still knows what has to be done in energy and resource policy in each case. But this is a misconception and can be shown by two simple and admittedly provocative examples.
Reducing the consumption of South American beef steaks in Germany, which is known to be particularly harmful to the climate, does not contribute to achieving the national climate protection goals in Germany. This measure is not considered in any official balance sheet, and the emissions saved would be outside the German territory. Nevertheless, it makes sense from a global climate perspective. The chemical and pharmaceutical industry contributes 40 million tons annually to Germany's CO2 emissions (VCI 2021). If they were closed, this would be positive for the German carbon footprint, but the chemicals would be produced elsewhere in the world. Germany would then probably even cover its chemical needs through increased imports. But this would not be considered in any official balance sheet in Germany.
For the last example, a few more figures (Fig. 2): Assuming the dozen most important chemicals currently produced in Germany, we come up with emissions of 28 million t CO2 per year. A large amount that could be saved. If the same amount were then produced in China, assuming current emission factors, CO2 emissions would be 56 million tons per year, twice as high. Even if we assume that the chemicals would then be produced in the USA, the value would still be 30 million tons of CO2, i.e. higher than in Germany. This would therefore make no sense in terms of global climate protection. Nevertheless, the relocation of the chemical industry would be considered positive from a purely balance sheet perspective.
The climate impact of the circular economy can also only be sensibly assessed in a global context. For example, if recycling is seen as a contribution to the supply reliability of raw materials, the material cycles should be closed in Germany or at least in Europe. This is because a processing of secondary raw materials in the Far East would lead to further economic dependencies. However, this would mean that recycling would lead to more emissions in Europe, but, elsewhere in the world, it would result in significant savings through subsequent reduction of primary raw material extraction.
The accounting of GHG emissions we are responsible for through our actions in Germany must therefore always consider the global dimension, because otherwise measures will be misjudged. While the territorial balance reflects the direct emissions and above all the emissions caused by fossil energy use, the carbon footprint of raw materials and materials can only be realistically estimated using life cycle approaches and global balances. In the future, both energy and material use must be considered systemically.
This leads us to the subject of this issue. It is the result of a cooperative doctoral program in Baden-Württemberg, which was conducted between different research groups and served, among other things, the exchange of different professional perspectives. At the Karlsruhe Institute of Technology (KIT), the research group led by Prof. Dr. Wolf Fichtner deals with energy system modeling, mainly from a macro perspective. Prof. Dr. Armin Grunwald heads the KIT Institute for Technology Assessment and Systems Analysis. Prof. Dr. Ursula Eicker headed a working group at the Stuttgart University of Applied Sciences until 2019, dealing with renewable energy systems from a micro perspective. The Institute for Industrial Ecology (INEC) at Pforzheim University of Applied Sciences with Prof. Dr. Mario Schmidt and Prof. Dr. Ingela Tietze, on the other hand, has a stronger focus on the material metabolism of the industrial society and the resource topic. It has its background in the field of life cycle assessment. All participants of the research group share a systemic approach and an interdisciplinarity that overcomes disciplinary boundaries. Through the work on energy systems on the one hand and raw material topics on the other, important bridges were built between the researchers and impulses for thought were given. There were discussions among the young scientists, including joint publications. In some cases, the new findings were reflected in the doctoral theses, in which these different perspectives were more closely integrated or calculation models were expanded accordingly. But it is only a beginning, as each discipline has already built highly complex models. Further work will have to be done on these topics.
The doctoral program "Energy Systems and Resource Efficiency" was financed by the Ministry of Science and Culture of the State of Baden-Württemberg within the framework of the state graduate funding from 2016 to 2020. A total of 12 scholarship holders received funding. By April 2021, the doctoral program had produced over 30 peer-reviewed articles and just as many contributions in non-peerreviewed journals or at academic conferences. Some doctoral theses have already been successfully completed, others are currently in the final phase. This publication gives young scientists the opportunity to present their research topics. The contributions were also all subject to a review process.
Philipp Schäfer's dissertation, which has since also been published as a book (Schäfer 2021), addresses the important question of what purpose the recycling of materials serves. In the Circular Economy, which is currently popular in the public and in politics, the emphasis is too quickly placed on secondary indicators such as the degree of recycling. But it neglects the question of how far recycling actually contributes to a reduction in environmental impact and can really close a supply gap in raw materials. Schäfer does point out the limits of recycling, but in doing so he also sets out the framework where recycling is necessary and still needs to be expanded in order to promote climate protection, for example. Important indicators are energy demand and the carbon footprint of raw material extraction-both in mining and recycling. Nadine Rötzer follows up on these questions (Rötzer 2021), builds on the methodology of the life cycle approach and treats the primary extraction of copper as a case study. She creates a generic and parameterized model of copper extraction, which is used to include significant influencing factors such as the copper content in the ore, geological or technical aspects and to understand their impact on the energy demand. The important indicator here is the cumulative energy demand (CED). As a result, it provides concrete data for copper supply for Germany.
In her work, Marlene Preiß switches from the basic perspective to the shop floor in manufacturing companies (Preiß 2021). The project "100 Companies for Resource Efficiency" (Schmidt et al. 2019) and methodological approaches such as material flow cost accounting (Guenther et al. 2015) have already shown what contribution companies can make to climate change mitigation through operational efficiency measures. Much has already been written about energy efficiency measures, their drivers and barriers. Less detailed research has been done on the success factors of material efficiency in companies. Marlene Preiß can draw on a large pool of case studies. One interesting aspect is the networking of companies along the value chain, which is currently also playing an increasingly important role in connection with the determination of GHG emissions, the so-called Scope 3 emissions .
Phosphorus is a raw material that is indispensable not only for the economy, but for humanity as a whole. Many, often dystopian, stories are woven around it, because current extraction and use is far from sustainable management. Here, Roukaya Issaoui bridges the gap between the extraction of phosphate in North Africa and the technologies for phosphorus recovery from wastewater (Issaoui et al. 2021). The methodological basis is Life Cycle Assessment, which uses many indicators to evaluate the environmental impact.
Jasmin Friedrich is also working on wastewater systems (Poganietz et al. 2021), which on the one hand contribute significantly to public health in municipalities, but are also energy and resource intensive and do not recover nutrients efficiently and effectively. She is investigating alternative systems that separate wastewater into gray and black water, but more importantly, these systems can also utilize energy by connecting it to biogas plants and recover resources more efficiently. The integrated water-energy-waste systems are analyzed based on the so-called eco-efficiency.
How can the heat demand of buildings in municipalities be simulated, the possible use of centralized and decentralized supply systems be examined, and local decisionmakers be supported in the process? In her work, Verena Weiler addresses these questions (Weiler and Eicker 2021). One focus of it is the development of a data model for energy system components to enable automatic simulation. The data model is set up in such a way that, for the future, the material input of the energy-technical components can also be considered as the quantity of steel, insulation, cables, etc.
The time component is of central importance in supplying urban neighborhoods and entire cities with electricity. Sally Köhler has extended the established simulation environment SimStadt with the development of a current load profile generator with variable resolution and an hourly PV potential analysis with variable economic analysis (Köhler et al. 2021). This enables the parallel evaluation of the potential of photovoltaics with the associated investment and operating costs over the lifetime of hundreds of individual buildings. In the future, the simulation platform will support the development of granular sustainable energy concepts through a holistic, time-resolved and buildingspecific approach, thereby transforming the building stock in a sustainable and low-carbon manner.
How does one decide between the many alternative technologies and measures in the transformation of energy sys-tems in the future? Jann Michael Weinand points to the solution by mathematical optimization models (Weinand et al. 2021). He has created a typology for the energy systems to be examined. Based on this, he has selected representative energy systems, analyzed them in an energy system optimization model, and applied it to all other energy systems. Using this remarkable approach, he determined the minimum costs of the energy transition for all 11,131 German municipalities from 2015 to 2035 in the fully energy selfsufficient case. The methodology is well suited to estimate which municipalities are particularly suitable for energy autonomy and how their energy systems could be designed.
Daniel Fett analyzes the user acceptance of PV battery storage and its major influencing factors (Fett et al. 2021).
Empirical results indicate that the acceptance of PV battery storage is mainly influenced by beliefs, knowledge about battery storage, user-friendliness, and benefits of PV battery storage. Much depends on user perceptions, which is why it is so important to inform people about battery storage systems and provide sound information about current battery life and existing warranties.
As the last article in this issue, Jan Rafael Finck deals with the complex topic of the European electricity market (Finck 2021). Stock exchange capacities have a significant impact on market prices, exchanges, and the energy mix, and thus also determine the carbon footprint of electricity generation. Finck presents a framework for modeling flowbased market coupling and analyzes, among other things, the impact of different levels of regulatory induced minimum trading capacities.
At this point, we would like to thank all other colleagues who have actively contributed to the doctoral program through discussions and supervision, in particular Prof. Dr. Armin Ardone, Dr. Helmut Lehn, Prof. Dr. Russell McKenna, Dr. Witold-Roger Poganietz, Dr. Christine Rösch, Prof. Dr. Tobias Viere and Prof. Dr. Jörg Woidasky. Special thanks go to the state of Baden-Württemberg and the Ministry of Science and Culture for funding the doctoral program.
Funding Open Access funding enabled and organized by Projekt DEAL.