Publications

Description

Germany aims to be greenhouse gas neutral by 2045 and negative from 2050 onwards. To achieve this, emissions which cannot be avoided or are very hard to avoid — so‐called residual emissions— must be balanced out with “negative emissions”. The way to do this is the targeted removal of CO₂ from the atmosphere (Carbon Dioxide Removal, CDR). To remove sufficient CO₂, it is necessary to incentivize CDR processes and projects through appropriate policy instruments—such as regulations, funding programs, or public information campaigns. Developing and implementing these policy instruments poses a challenge for decision‐makers. This new assessment framework for policy instruments can assist in this process. In it, the authors propose fifteen guiding questions that decision‐makers should use for orientation when developing policy instruments to control, promote, and regulate CDR. These guiding questions help incorporate various societal values and goals into the decision‐making process and enable transparent and traceable communication of decisions.

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In this study a systematic literature review of assessment frameworks used for climate change responses was conducted, analyzing how they address what the authors identified as key requirements. By expanding the scope beyond CDR specific assessment frameworks, the authors identify and derive valuable insights and approaches that can inform their refinement. Following a three-step approach, they first conducted a preceding scoping review to determine key requirements for holistic assessments. Second, a systematic literature review was conducted to identify a broad range of assessment frameworks for climate responses. Third, based on a qualitative content analysis, the authors examined how these frameworks address the previously identified key requirements.

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In this study, the authors compare two complementary approaches that enhance the terrestrial and marine carbon sinks with afforestation and reforestation (A/R) and ocean alkalinity enhancement (OAE), respectively, under the high emission scenario SSP5-8.5. Eight CMIP6 Earth system models are utilized, enabling a quantification of both inter-model and internal variability.

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The authors present a novel assessment framework designed for mCDR options. The framework provides important conceptual advancements to existing frameworks currently used to assess climate options: It clearly distinguishes between and allows for the assessment of both the feasibility and desirability of mCDR options, it makes explicit the evaluative standards upon which the assessment is based and it separates the descriptive listing of information from the evaluation of said information. The assessment framework aims to advance the debate on what role mCDR can and should play in responding to the climate crisis by providing a tool for both policymakers and stakeholders to assess mCDR options in a transparent and comprehensive way.

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The current literature on assessing climate change response options does not sufficiently distinguish between assessing options in terms of their feasibility and in terms of their desirability. One example of this is the IPCC feasibility assessment framework. The authors argue that assessments of climate response options should indeed cover questions of desirability, but they should do so explicitly. Transparency about underlying normative standards is the key to a productive desirability assessment.

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The LiDELS (LiBry-DETECT Layer Scheme) model offers a process-based approach to assess these soil-vegetation interactions and the potential for carbon sequestration in response to biochar application under diverse environmental conditions. This study presents an overview of the LiDELS model and its application to a sandy soil profile under the climate conditions of northern Germany. LiDELS simulates the impacts of biochar on key soil functions, including water retention, thermal properties, evapotranspiration rates, and net primary production (NPP).

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In this paper, the authors introduce a comprehensive assessment framework designed to evaluate the feasibility and desirability of various policy instruments for governing CDR. The framework is structured around 15 criteria, some of which are value-based, and organized into six key dimensions of interest. This framework is suitable for application at different stages of policy deliberation, planning, and development. It can be utilized by policymakers, legislators, and administrators, as well as stakeholders aiming to influence the direction of CDR governance.

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The AR6 Scenarios Database is a vital repository of climate change mitigation pathways used in the latest Intergovernmental Panel on Climate Change (IPCC) assessment cycle. In its current version, many scenarios in the database lack information about the level of anthropogenic carbon dioxide (CO₂) removal via land sinks, as net-negative CO₂ emissions and gross removals on land are not always separated and are not consistently reported across models. This makes scenario analyses focusing on CO₂ removal challenging. The authors test and compare the performance of different regression models to impute missing data on land carbon sequestration for the global level and for several sub-global macro-regions from available data on net CO₂ emissions from agriculture, forestry, and other land uses.

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Die in diesem Policy Brief vorgestellten Empfehlungen wurden auf der Grundlage der Ergebnisse eines zweitägigen Stakeholder-Workshops entwickelt, der vom 18. bis 19. April 2023 in Berlin stattfand, sowie einer anschließenden Online-Umfrage. Die Teilnehmenden waren hauptsächlich Expert*innen, die sich mit der europäischen und deutschen Klimapolitik beschäftigen.

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CDR generally and DACCS specifically are complex and uncertain topics, with an immense divergence of views and values on how to proceed (or not) with their implementation. Concerns abound about these technologies’ mitigation potential and co-benefits, as well as fear they distract from emissions reduction priorities. The recommendations presented in this policy brief were developed based on results from a two-day stakeholder engagement workshop that took place in Berlin from April 18-19, 2023 and a subsequent online survey. Participants were experts mainly engaged in European and German climate policy.

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This exploratory study provides insights into the stakeholder engagement process of a transdisciplinary research project and its findings regarding co-creative CDR policy design and evaluation. It analyzes the views of participants in a stakeholder engagement workshop on CDR and an online survey. In all instances, experts highlighted the importance of the context in which these technologies are deployed. Workshop participants’ views of DACCS, including its risks and opportunities, evolved throughout the process, indicating that learning took place. The authors also present stakeholders’ reflections on their own role in knowledge creation and policy design. The qualitative experience and joint exploration of topics reaffirm the relevance of proper engagement on controversial, wicked problems such as the scaling of CDR as exemplified for DACCS. A nuanced discussion of the deployment context matters for stakeholders’ perception of DACCS.

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In this policy brief The authors share recommendations for stakeholder engagement both in the research and in the development and implementation of CDR, as well as CDR-related policy making. The recommendations are based on learnings from active stakeholder engagement in Germany and other European countries.

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The authors analyzed six carbon farming measures on cropland in the European temperate zone: (1) cover cropping, (2) introducing legumes or semi-perennial crops into crop rotations, (3) conversion to short rotation coppice, (4) agroforestry, (5) afforestation of marginal cropland, and (6) partial rewetting of drained organic soils. Through a structured literature review, they derived on-site climate change mitigation potentials, impacts on the supply of ecosystem services, and economic trade-offs, as well as influencing factors causing spatial heterogeneities.

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Der Policy Brief geht von den aktuellen Stoffströmen des Bioenergiesystems aus und untersucht, inwieweit das Bioenergiesystem für die nachhaltige Bereitstellung von Carbon Dioxid Removal (CDR) genutzt werden kann.

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The electrochemical reduction of CO₂ is a promising realization of negative emissions to mitigate climate change, aiming at the efficient production and safe long-term storage of carbon-rich sink products. This approach, however, necessitates novel catalyst materials specifically targeting electrochemical carbon dioxide removal. In this work, we investigate synthesis routes for a cerium-incorporated GaInSn-based liquid metal catalyst, focusing on the electrochemical production of graphitic carbon. Preparation and preconditioning of the catalyst are found to be crucial for carbon production, while trace amounts of H₂O and OH in the organic electrolyte play a decisive role in the efficiency of the electrocatalytic process. Finally, for a better understanding of the reaction mechanism and the involved active species, experimental findings and density functional theory-based calculations are combined, suggesting a two-step reduction pathway with Ce(OH)x as the catalytically active surface species.

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In the study, the authors introduce different measures of efficiency to evaluate the carbon removal potential of afforestation and reforestation (AR) and bioenergy with carbon capture and storage (BECCS) under the low-emission scenario SSP1-2.6 and in the same area. They define efficiency as the potential to sequester carbon in the biosphere in a specific area or store carbon in geological reservoirs or woody products within a certain time. In addition to carbon capture and storage (CCS), we consider the effects of fossil fuel substitution (FFS) through the usage of bioenergy for energy production, which increases the efficiency through avoided CO₂ emissions.

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Biological nitrogen fixation (BNF) by symbiotic and free-living bacteria is an important source of plant-available nitrogen (N) in terrestrial ecosystems supporting carbon (C) sequestration and food production worldwide. Dynamic global vegetation models (DGVMs) are frequently used to assess the N and C cycles under dynamic land use and climate. BNF plays an important role in the components of both these cycles, making a robust representation of the processes and variables that BNF depends on important to reduce uncertainty within the C and N cycles and improve the ability of DGVMs to project future ecosystem productivity, vegetation patterns or the land C sink. Still, BNF is often modelled as a function of net primary productivity or evapotranspiration, and the actual drivers are neglected. The authors implemented plant-functional-type-specific limitations for BNF dependent on soil temperature and soil water content, as well as a cost of BNF, in the Lund–Potsdam–Jena managed Land (LPJmL) DGVM and compared the new (“C-costly”) against the previous (“Original”) approach and data from the scientific literature.

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At GERICS, researchers are currently running two projects that focus on this precisely. Within the DACStoreE project, GERICS focuses on the public perception of a novel Carbon Dioxide Removal method called Direct Air Capture and Storage (DACS). Within the project CDRSynTra GERICS investigates what agricultural implementers think of conventional and novel Carbon Dioxide Removal methods and what information they are missing. Within two projects, GERICS is currently exploring stakeholders’ perspectives and knowledge needs regarding DACS and carbon dioxide removal practices in the agricultural sector. This is a necessary measure to facilitate its implementation. With their studies, the authors pave the way for an intensive exchange between researchers and local stakeholders to work together to push forward Carbon Dioxide Removal in Germany.

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A successful implementation of Carbon Capture, Transportation, Utilization, and Storage (CCTS/CCUS) projects depends on proactively communicating to and engaging with the public and relevant stakeholders. Based on the authors’ research in the framework of a pilot project demonstrating two complementary CCTS/CCUS pathways for Switzerland, they underpin this importance and present and exemplify nine recommendations for communication and stakeholder engagements.

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Here the authors show that global and regional climate change and associated risks after an overshoot are different from a world that avoids it. They find that achieving declining global temperatures can limit long-term climate risks compared with a mere stabilization of global warming, including for sea-level rise and cryosphere changes. However, the possibility that global warming could be reversed many decades into the future might be of limited relevance for adaptation planning today. Temperature reversal could be undercut by strong Earth-system feedbacks resulting in high near-term and continuous long-term warming.

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While it is critical to learn from the existing evidence on CDR policy and governance, there is no overview of this dispersed body of literature right now. This work addresses this lack of overview by systematically mapping the literature assessing policy and governance dimensions of CDR. Systematic mapping provides a comprehensive view of a research field by analysing the state of evidence, i.e. how much research is available at any point in time on which topics and geographies studied by whom, when and where. The authors use an AI-enhanced approach to systematic mapping, trimming down an initial set of about 30,000 documents on CDR to a set of 876 that deal with governance and policy issues.

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To assess DACCS performance holistically, a detailed global analysis is needed that accounts for the interplay of regional ambient conditions, energy supply, and CO2 storage potential. Hence, the authors present a novel method for the optimal siting of DACCS plants derived from optimising a dynamic process model that uses global hourly weather data and regionalised data on electricity supply and CO2 storage potential. The carbon removal rate (CRR) measures the climate benefit and describes the speed at which a DACCS plant generates net negative emissions.

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Here, the authors develop an ambitious Afforestation/Reforestation scenario by harnessing 1259 Integrated Assessment Model scenarios, restoration potential maps, and biodiversity constraints, reaching 595 Mha by 2060 and935 Mha by 2100. They then force the Max Planck Institute’s Earth System Model with this scenario which yields a reduction of peak temperature by 0.08°C, end-of-century temperature by 0.2°C, and overshoot duration by 13 years. Afforestation/Reforestation in the range of country pledges globally could thus constitute a useful mitigation tool in overshoot scenarios in addition to fossil fuel emission reductions, but socio-ecological implications need to be scrutinized to avoid severe side effects.

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Bio-based carbon dioxide removal encompasses a range of (1) natural sink enhancement concepts in agriculture and on organic soils including peatlands, and in forestry, (2) bio-based building materials, and (3) bioenergy production with CO2 capture and storage (BECCS). A common database on these concepts is crucial for their consideration in strategies and implementation. In this study, we analyse standardised factsheets on these concepts. We find different dynamics of deployment until 2045: for CO2 removal rates from the atmosphere, natural sink enhancement concepts are characterised by gradually increasing rates, followed by a saturation and potentially a decrease after few decades; forest-related measures ramp up slowly and for construction projects and bioenergy plants, annually constant removal rates are assumed during operation which drop to zero afterwards. The expenses for removing 1 t CO2 from the atmosphere were found to be between 8 and 520 € t CO2−1, which arises from high divergence both in capital and operational expenditures among the concepts. This high variability of expenses seems to suggest the more cost-effective concepts should be implemented first. However, aspects from economics, resource base and environmental impacts to social and political implications for Germany need to be considered for developing implementation strategies. All concepts investigated could be deployed on scales to significantly contribute to the German climate neutrality target.

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To bridge the knowledge and perspective gap between decision-makers, practitioners, and rural communities in tropical forest frontiers, the authors developed an innovative tool based on serious games. The game is based on a case study of smallholder farmers in the Peruvian Amazon and simulates local socio-ecological dynamics allowing for reflection and collective learning among participants. By testing the tool in academic settings, they observed that it facilitates extensive reflections and dialogues, allowing players to better understand and reflect on the difficulties of making sustainable land use decisions in challenging contexts.

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In this article, the authors undertake a political economy-based analysis of the historical development and structural conditions of German climate policy measures and their enabling role for the emergence and strengthening of carbon dioxide removal policy options. They refer to regulation theory and the Modell Deutschland approach and argue that within this model the concept of ecological modernization has been established as the dominant approach to regulate society-nature relations. In light of the ambitious climate policy goals, such as net zero by 2045, ecological modernization reaches its current limits and must be recalibrated. Against this background, the authors conclude by discussing the risk of mitigation deterrence associated with carbon dioxide removals and considering alternative pathways, such as degrowth, to social ecological transformation.

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The scientific community has explored the characteristics of greenhouse gas emission reduction pathways in line with the Paris Agreement. However, when categorizing such pathways, the focus has been put on the temperature outcome and not on emission reduction objectives. Here the authors propose a pathway classification that aims to comprehensively reflect the climate criteria set out in the Paris Agreement. They show how such an approach allows for a fully consistent interpretation of the Agreement. For Paris Agreement compatible pathways, the authors report net zero CO₂ and greenhouse gas emissions around 2050 and 2065, respectively. They illustrate how pathway design criteria not rooted in the Paris Agreement, such as the 2100 temperature level, result in scenario outcomes wherein about 6 – 24% higher deployment (interquartile range) of carbon dioxide removal is observed.

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Although the Paris Agreement states that climate change mitigation must be done “in the context of sustainable development”, most scenarios do not explicitly consider social and environmental sustainability. The authors therefore identified a subset of scenarios that can be considered “more sustainable”. Across this group of scenarios, the central range of CDR deployment is 7 to 9 GtCO₂ per year in 2050. The lowest scenarios reach 4 GtCO₂ per year in 2050. While this range is similar in 2050 to that for all below 2°C scenarios, the more sustainable scenarios cumulatively remove 170 GtCO₂ between 2020 and the time of net zero CO₂, compared with 260 GtCO₂ cumulatively in all below 2°C scenarios.

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The authors use an integrated land system model to explore the effects of large-scale bioenergy production within the European Union on carbon balances. They find that increased bioenergy crop production is likely to cause substantial deforestation and a commensurate loss of associated carbon stocks largely due to displacement of food production from other areas. Deforestation would occur either within the EU if European forests were not protected, or in other parts of the world arising from indirect land use change if European forests were protected. The net carbon benefit of bioenergy production is largely negative, or uncertain, even under the most optimistic levels of fossil fuel replacement, and will not offset initial carbon losses over the coming 50 yr. The growth of intensive agriculture required to satisfy the demand for bioenergy and food will have negative impacts on crucial ecosystem services.

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This paper aims to address this research gap by comparatively examining the development of biomass-based CDR in three regions of Germany. Taking an exploratory approach, we conducted surveys in these regions to gain insight into stakeholder perceptions of the following six CDR methods: forest management, agriculture and soil carbon, long-lasting building materials, rewetting of peatlands and paludiculture, biochar, and bioenergy with carbon capture and storage. In this article, the authors present the results of the stakeholder survey, which offers multiple perspectives that can shape future studies of regional implementation and yield policy-relevant guidance. Although the research primarily focuses on the regional level in Germany, it sheds light on various conflicts, uncertainties, and potentials that are likely to be relevant for the rollout of CDR in other countries.

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Here, with the aim of supporting the path to achieving net-zero emissions in cities, the authors assess the existing literature on carbon dioxide removal (CDR) at the urban scale, seeking to quantify the potential negative emissions contribution of cities globally. Urban CDR options considered here include the storage of carbon in urban vegetation, soils and buildings, and the capture of CO₂ from indoor environments via decentralized direct air capture. Our estimates of carbon storage and capture potentials indicate that deploying CDR options at the urban scale could make a substantial contribution to global mitigation of climate change, alongside supporting the upscaling of climate action from local to regional and national scale.

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Scenarios compatible with the Paris agreement’s temperature goal of 1.5 °C involve carbon dioxide removal measures – measures that actively remove CO₂ from the atmosphere – on a massive scale. Such large-scale implementations raise significant ethical problems. Van Vuuren et al. (2018), as well as the current IPCC scenarios, show that reduction in energy and or food demand could reduce the need for such activities. There is some reluctance to discuss such societal changes. However, they argue that policy measures enabling societal changes are not necessarily ethically problematic. Therefore, they should be discussed alongside techno-optimistic approaches in any kind of discussions about how to respond to climate change.

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The latest science shows that, to stop global warming, we must reach “net zero” emissions by 2050. This means that any carbon dioxide (CO₂) humans are still releasing into the atmosphere in 2050 would need to be balanced out by taking CO₂ from the atmosphere and locking it away. The process of removing CO₂ from the atmosphere is called carbon dioxide removal (CDR). This article will explain why CDR is needed and will introduce some methods of removing CO₂, including the strengths and weaknesses of those methods. There are many actions we can take. Many bring lots of other benefits, while some have drawbacks too. But overall, Carbon Dioxide Removal has a big role to play in successfully tackling climate change.

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Given the high rates of deforestation in the Amazon region, it is important to study under which conditions Payments for environmental services (PES) have positive environmental and social outcomes. The authors contribute to this debate through a systematic review based on the Realist Evaluation framework. First, they review case studies to identify configurations of social-ecological factors (context), PES design and implementation (resource mechanisms), people’s responses (reasoning mechanisms), and the results in terms of forest conservation and people’s livelihoods (outcomes). Second, they develop a middle-range theory of how, for whom, and under what conditions PES in the Amazon achieve these results.

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In this report, the authors look to the possible versions of a future with carbon removal, imagining its best forms, its worst forms, and its most likely forms. As they take stock of the path that the sector is currently on, they worry that carbon removal might result in harms and injustices—or simply fail to be effective. On the other hand, the authors can also envision a future in which carbon removal serves as a tool for progressive principles like real climate action, justice, labor and economic rights, democratic participation, and wealth redistribution.

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Carbon dioxide removal (CDR) – the creation, enhancement, and upscaling of carbon sinks – has become a pillar of national and corporate commitments towards Net Zero emissions, as well as pathways towards realizing the Paris Agreement’s ambitious temperature targets. In this perspective, the authors explore CDR as an emerging issue of Earth System Governance (ESG). They draw on the results of a workshop at the 2022 Earth System Governance conference that mapped a range of actors, activities, and issues relevant to carbon removal, and refined them into research questions spanning four intersecting areas: modeling and systems assessment, societal appraisal, policy, and innovation and industry. They filter these questions through the five lenses of the ESG framework and highlight several key ‘cross-cutting’ issues that could form the basis of an integrated ESG research agenda on CDR.

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The report looks at how stronger implementation can increase the chances of the next round of NDCs, due in 2025, bringing down greenhouse gas emissions in 2035 to levels consistent with 2°C and 1.5°C pathways. It also looks at the potential and risks of Carbon Dioxide Removal methods – such as nature-based solutions and direct air carbon capture and storage.

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“This policy report seeks to map the status quo and propose a typology of policy measures and bundles that can be used to help address the challenging questions on permanence, and tradeability in CDR policymaking.”

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Carbon Dioxide Removal (CDR) is a key element of any mitigation strategy aiming to achieve the long-term temperature goal of the Paris Agreement, as well as national net-zero and net-negative greenhouse gas emissions targets. For robust CDR policy, the credibility of certification schemes is essential.

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After the adoption of a EU-wide net-zero greenhouse gas emissions target, the issue of carbon dioxide removal (CDR) is climbing up the EU climate policy agenda. Based on an analysis of CDR-related aspects of the Climate and Energy Framework 2030 and new actor positions in the context of the European Green Deal, the chapter traces the emergence CDR policymaking in the EU. The authors find that CDR is not entirely new in EU climate policy. Recently, spurred by the new climate target structure in the EU climate law, new CDR initiatives, processes and debates have been launched. The analysis shows that prospects of CDR policymaking will be shaped by ‘geographies of net zero’: Differences and conflicts over climate targets, composition of residual emissions, removal capacities, and socio-political preferences for different CDR methods in EU member states will affect future legislation.

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Questions around the technical and political feasibility of deep mitigation scenarios assessed by the Intergovernmental Panel on Climate Change have increasingly been raised as have calls for more directly analyzing and incorporating aspects of justice and fairness. Simultaneously, models are increasing the technical representation of novel carbon-dioxide removal (CDR) approaches to provide policy-relevant analyses of mitigation portfolios in the context of the rising number of net-zero CO2 and GHG targets made by parties to the Paris Agreement. Still, in most cost-effective mitigation scenarios developed by Integrated Assessment Models, a significant portion of mitigation is assumed to take place in developing regions. We address these intersecting questions through analyzing scenarios that include Direct Air Capture of CO2 with Storage (DACCS), a novel CDR technology that is not dependent on land potential and can be deployed widely, as well as regional variations in institutional capacity for mitigation based on country-level governance indicators. We find that including novel CDR and representations of institutional capacity can enhance both the feasibility and fairness of 2°C and 1.5°C high-overshoot scenarios, especially in the near term, with institutional capacity playing a stronger role than the presence of additional carbon removal methods. However, our results indicate that new CDR methods being studied by models are not likely to change regional mitigation outcomes of scenarios which achieve the 1.5°C goal of the Paris Agreement. Thus, while engineering carbon removals like DACCS may play a significant role by midcentury, gross emissions reductions in mitigation pathways arriving at net-zero CO2 emissions in line with 1.5°C do not substantially change. Our results highlight that further investment and development of novel CDR is critical for post-net-zero CO2 mitigation, but that equitable achievement of this milestone will need to arrive through technical and financial transfers, rather than by substantial carbon removals in developed countries.

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International carbon markets are potentially a very powerful tool for mobilizing carbon dioxide removal in line with Paris Agreement ambitions to limit global warming to well below 2°C. This requires reaching global net-zero emissions between 2050 and 2070. Yet, carbon market regulators have not approached removals in a systematic manner. This review assesses the highly fragmented treatment of removals under compliance and voluntary carbon markets, including baseline, credit and cap-and-trade systems. The Kyoto mechanisms and the large voluntary carbon market standards have long focussed on biological removals without inherent storage permanence and only recently started to develop methodologies for removals with geological storage, mineralization or biochar. Driven by high prices for credits from emerging removal technologies and advance market commitment initiatives targeting high permanence removals, various newcomers in voluntary markets are currently establishing their own approaches for generating removal credits. However, they disregard key concepts safeguarding market quality such as additionality, which risks triggering scandals and tainting the entire market for removal credits. Given the diversity of credit prices spanning three orders of magnitude from 1 to 1000, as well as of volumes ranging from a few hundred to tens of millions of credits, the current “gold rush” atmosphere of removal markets needs to quickly be replaced by a coordinated approach, ensuring credibility, and enabling removals to play the required role in reaching global net zero.

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Die Klimapolitik in der Europäischen Union und in Deutschland hat sich mit der Verabschiedung von Netto-Null-Zielen deutlich verändert. Eine neue Entwicklung ist die Bedeutung von Carbon Management. Der Sammelbegriff umfasst neben der Ab­scheidung und Speicherung von CO₂ (Carbon Capture and Storage, CCS) auch die CO₂‑Abscheidung und Nutzung (Carbon Capture and Utilization, CCU) sowie die Ent­nahme von CO₂ aus der Atmosphäre (Carbon Dioxide Removal, CDR). Es ist wichtig, Klarheit in Bezug auf die Abgrenzung dieser einzelnen Ansätze zu schaffen und ihr Verhältnis zu den sogenannten Restemissionen und schwer vermeidbaren Emissionen zu identifizieren. Dies ist insbesondere deshalb ratsam, weil davon das generelle Ambitionsniveau der Klimapolitik, die zukünftige Ausgestaltung der Politikdesigns sowie deren Verteilungswirkungen abhängen. Aktuelle Politik- und Gesetzgebungsprozesse sollten genutzt werden, um darauf hinzuwirken, dass Carbon Management den Ausstieg aus fossilen Energieträgern nicht verlangsamt. Die neuen Initiativen bieten die Gelegenheit, die Schnittstelle zwischen ambitioniertem Klimaschutz und Industriepolitik aktiv zu gestalten.

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We compute the social cost of carbon (SCC) when decision makers want robust estimates in the face of deep (or “Knightian”) uncertainty. We introduce the notion of full-path accumulated robust preferences from stochastic control theory to an integrated assessment model. Robust preferences are appropriate for analyzing climate-related problems because, given the large uncertainty in climate science, they enable decision makers to attain solutions that are robust to a wide range of climate change scenarios. We solve the resulting model, which includes uncertainty about climate change and the ensuing economic damage and show the existence of optimal solutions and time-consistent optimal deterministic Markov policies. Additionally, we also prove that the standard Hansen–Sargent recursive utility provides an upper bound of this full-path utility. In our baseline model specification, we find that the year 2020’s optimal SCC is US$162 per tCO2 with an average annual growth rate of 2.5%, setting the world on a 1.37°C path, which requires full decarbonization by 2068. We introduce the notion of the SCC robustness premium, which we define as the additional SCC price tag for robustness. For a plausible range of preference parameters, the SCC robustness premium in 2020 is between US$1.41 and US$25.89 per tCO2 with US$2.20 per tCO2 in our baseline calibration. Over time, this premium grows significantly. The forecasts of our model facilitate managerial decision making during the world’s transition from a carbon- and emission-intensive economy to a regenerative economy. The high estimates for the SCC predict drastic rises in emission costs for high-emission industries.

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Although still relatively scarce, empirical studies on the emergence of carbon dioxide removal (CDR) on the political agenda have shown that variations in the constellations and positions of policy-relevant actors play a key role in shaping patterns of CDR policymaking. The German and wider European Union (EU) CDR policy space is emergent, and political actors are just beginning to position themselves. Building on their previous work which established a typology of CDR policy integration patterns and developed a discourse analytical framework for mapping CDR-policy-relevant speaker positions, the authors present the first fine-grained empirical reconstruction of CDR-policy-relevant actors and their positions in the German context. Their analytical approach aims to improve understanding of patterns in CDR policymaking by showing that on the EU, national, and subnational levels, a multitude of institutional actors may adopt differing positions as the CDR policy space evolves. In addition to identifying fine-grained ‘ideal types’ of positions that policy actors may adopt in the formative phase of German CDR policy, the analysis provides an empirical ‘map’ of CDR policy-relevant actors and explores hypotheses about emerging discourse coalitions and potential conflict cleavages.

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Carbon dioxide removal technologies are gaining prominence in academia, industry and policy, yet the need for substantial funding raises serious challenges. This comment outlines these issues and charts a path for the effective, systematic and fair mobilization of funds for removals.

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Drawing together analysis across several key areas, this report is the first comprehensive global assessment of the current state of CDR. The authors find a gap between how much CDR countries are planning and what is needed in scenarios to meet the Paris temperature goal. The size of the “CDR gap” differs across scenarios, depending on how we choose to transform the global economy towards net-zero emissions. However, there are currently few plans by countries to scale CDR above current levels, exposing a substantial shortfall. CDR involves capturing CO₂ from the atmosphere and storing it durably on land, in the ocean, in geological formations or in products. Examples include reforestation, biochar, Bioenergy with Carbon Capture and Storage (BECCS) and Direct Air Carbon Capture and Storage (DACCS). For the first time, this report compiles an estimate of the total amount of CDR currently being deployed around the world.

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Der Begriff „negative Emission“ bezeichnet das aktive Entfernen von Kohlendioxid aus der Atmosphäre und das langfristige Speichern des Kohlendioxids oder des darin enthaltenen Kohlenstoffes, um den Treibhauseffekt und damit die Erderwärmung zu begrenzen. Negative Emissionen von Kohlendioxid sind wesentlicher Teil nahezu aller Szenarien, mit denen die Pariser Klimaziele noch erreicht werden können, und sie sind in vielen Zu­sagen der Nationalstaaten enthalten – auch der Europäischen Union und Deutsch­lands (IPCC WG III, 2022, Erlach et al., 2022, Bundes-Klimaschutzgesetz 2021). Die benötigte negative Emission ist über sehr viele Jahre hinweg absehbar be­eindruckend hoch, konkrete Werte hängen davon ab, wie schnell es uns global gelingt, weitere Emissionen von Treibhausgasen zu verringern. Obwohl sich die Staatengemeinschaft darauf geeinigt hat, die globale Erwärmung auf deutlich unter 2 Grad zu begrenzen, laufen die aktuellen Zusagen der Staaten, ihre Emissionen zu verringern, auf etwa 3 Grad Erwärmung hinaus (climateactiontracker.org). Die Vermutung, dass negative Emissionen zu­künftig ein­fach und ohne große Kosten oder Aufwand alle Klimaprobleme lösen, kann im schlimm­sten Fall als Begründung genutzt werden, die Emission von Treib­haus­gasen noch weniger oder gar nicht zu verringern. In diesem Kurzimpuls geben wir unter Berücksichtigung aktueller wissenschaftlicher Ver­öffentlichungen Antworten zu den Fragen „ist das notwendig?“, „welche Metho­den sind geeignet?“, sowie „wann und wie sollten wir damit beginnen?“ Dazu versu­chen wir einen Eindruck von der Größenordnung und den technischen Herausforde­rungen bei der Umsetzung negativer Emissionen zu vermitteln. Dieser Beitrag ist das Ergebnis einer umfangreichen Diskussion zu negativen Emis­sionen. Er wendet sich bewusst an Politik und die breite Öffentlichkeit. Im Vor­der­grund stehen daher Aspekte zu konkreten Handlungen und zu Ent­schei­dun­gen.

Description

Soil organic carbon (SOC), one of the largest terrestrial carbon (C) stocks on Earth, has been depleted by anthropogenic land cover change and agricultural management. However, the latter has so far not been well represented in global C stock assessments. While SOC models often simulate detailed biochemical processes that lead to the accumulation and decay of SOC, the management decisions driving these biophysical processes are still little investigated at the global scale. Here we develop a spatially explicit data set for agricultural management on cropland, considering crop production levels, residue returning rates, manure application, and the adoption of irrigation and tillage practices. We combine it with a reduced-complexity model based on the Intergovernmental Panel on Climate Change (IPCC) tier 2 method to create a half-degree resolution data set of SOC stocks and SOC stock changes for the first 30 cm of mineral soils. We estimate that, due to arable farming, soils have lost around 34.6 GtC relative to a counterfactual hypothetical natural state in 1975. Within the period 1975–2010, this SOC debt continued to expand by 5 GtC (0.14 GtC yr−1) to around 39.6 GtC. However, accounting for historical management led to 2.1 GtC fewer (0.06 GtC yr−1) emissions than under the assumption of constant management. We also find that management decisions have influenced the historical SOC trajectory most strongly by residue returning, indicating that SOC enhancement by biomass retention may be a promising negative emissions technique. The reduced-complexity SOC model may allow us to simulate management-induced SOC enhancement – also within computationally demanding integrated (land use) assessment modeling.

Description

Climate change mitigation actions, including those aimed at developing and scaling carbon dioxide removal (CDR) activities spanning the industrial, energy, and agroforestry sector, emerge in a context of internationally shared norms that include governance objectives, legal provisions and informal expectations, and societal expectations. Established governance principles provide normative orientation for policy including when targeting the development and scaling of CDR. Knowledge of these principles can guide effective discussion and evaluation of policy options. To facilitate discussion of mitigation options among experts and CDR practitioners, this study excerpts governance principles from legislative texts, the climate governance literature, and the CDR literature with relevance to CDR policy considerations. To illustrate the relevance of the governance principles found for evaluating policy options, we apply them to three technology groups of CDR: Bioenergy with Carbon Capture and Storage (BECCS), Direct Air Carbon Capture and Storage (DACCS), and forestry. This exercise indicates the importance of more intensive attention to the normative dimension of mitigation policies in ongoing deliberative and planning processes. Such efforts can help disentangle normative and factual dimensions and sources of (dis)agreement on the role of CDR in specific climate policy contexts.

Description

Carbon capture and storage (CCS) technologies are controversially discussed worldwide. Germany is no exception. Here, CO₂ storage is banned, although successful pilot plants were installed in the late 2000s. However, the recent burgeoning political interest in this technology prompts us to investigate why and how the (public) image of CCS technologies has changed over time and with regard to different CCS applications. For this purpose, we examine the coverage of CCS in German newspapers over the last 20 years on the basis of a quantitative analysis of about 4000 newspaper articles. A sample of 571 articles with different political orientations was studied qualitatively to analyse reporting on different CCS frames and actors. We find evidence that the media debate is shifting towards the application of CCS for negative emissions technologies and carbon removal. However, the negative image of CCS connected to coal fired power plants persists, suggesting that public and political support remain a problem for a technology fixed in binary negotiations for or against it.

Description

Mit der Umsetzung der neuen Netto-Emissionsziele für 2030 und 2050 im Rahmen des Europäischen Green Deal rückt die aktive Entnahme von CO₂ aus der Atmosphäre in den Fokus politischer Entscheidungs­träger. Dass Netto-Null-Ziele ohne den großskaligen Einsatz von Maßnahmen zur CO2-Entnahme (Carbon Dioxide Removal, CDR) nicht erreicht werden können, hat auch der Weltklimarat IPCC in seinem jüngsten Bericht zur Minderung des Klimawandels erneut dargelegt. In den vergangenen Jahren hat sich die politische Debatte in der EU rasant verändert. Mittlerweile fordern nahezu alle politischen Akteure einen neuen regula­to­rischen Rahmen für die Bindung von CO₂ als integralen Baustein der EU-Klimapolitik. Über die Frage, welche Methoden und Politikinstrumente dafür verwendet und welche Schwerpunkte gesetzt werden sollen, bahnen sich indes grundlegende Konflikte an. Auf EU-Ebene sind erste Ansätze für politische Allianzen erkennbar, die kurzfristig die Fit-for-55-Gesetzgebung prägen und mittelfristig die Debatte über die Ausgestaltung der Klimapolitik zwischen 2030 und 2040 vorstrukturieren werden.

Description

The remaining carbon budgets compatible with limiting global warming to 1.5 or 2 °C above preindustrial levels are shrinking rapidly. An already firmly anticipated, but highly controversial measure to mitigate this challenge is the large-scale implementation of negative emissions, removing carbon dioxide from the atmosphere. Many of the currently considered negative emission technologies (NET) are based on natural photosynthesis, associated with large land footprints. Photoelectrochemical carbon sinks, on the other hand, promise to combine high conversion efficiencies with versatile storage options. Efficient sink products differ from the products typically considered for solar fuels, which will require novel catalysts and device designs. The development of efficient devices also has to take into account climatic parameters of the local environment as especially the ambient temperature affects device operation. While still in an early stage of development, carbon drawdown by such an artificial photosynthesis approach could be a valuable extension of the portfolio of NET.