Negative Emissions Research Articles

Extended magenta aurora as revealed by citizen science

During large geomagnetic storms, red auroras are typically observed from low-latitude countries such as Japan. The color arises from a specific emission line of oxygen atoms at high altitudes. However, during the May 10-11th 2024 superstorm, magenta auroras were observed above Japan instead of the typical red. In this study, we demonstrate that the magenta hue is created by a mixture of red (O) and a blue (N2+) aurora at extremely high altitudes. The blue color originates from the N2+ first negative emission band caused by both resonant scattering of the upwelling molecular ions and heavy particle precipitation during the storm. This study is primarily driven by observations from citizen scientists, and confirmed and quantified with observations from spacecraft and modeling techniques. Additionally, we show that high solar activity, terrestrial season, and the preheating of the atmosphere all contribute to the occurrence of magenta aurora. This study showcases the value and richness of citizen science, and we anticipate that such approaches will become increasingly important in the future.

Asymmetric impact of climate change on banking system stability in selected sub-Saharan economies

This study is an empirical examination of the asymmetric impact of climate change on banking system stability in selected sub-Saharan economies. The study leverages a quantitative research approach through a panel non-linear ARDL framework and data from 29 selected economies, which spans 1996-2017. Findings from the study reveal that in the long term, partial sums of temperature have an insignificant relationship with banking system stability. Further, partial sums of precipitation are negatively related to banking system stability in the long term. The finding indicates that both positive and negative precipitation do harm banking system stability in the selected sub-Saharan economies. Moreover, we find that partial sums of greenhouse gas emissions had an insignificant relationship with banking system stability. In addition, we conclude that greenhouse gases (positive and negative) do not impair banking system stability in selected sub-Saharan economies in the long term. We surmise from the findings that both positive and negative climate change indexes are harmful to banking system stability. On the short-term asymmetric impact, we discover that partial sums of temperature, precipitation, and climate change index do not harm banking system stability. However, negative greenhouse gas emissions are pernicious to the banking system’s stability in the short term. Conversely, positive greenhouse gas levels were statistically insignificant. The study recommends that central banks and monetary authorities in Sub-Saharan Africa design green banking policies to push the climate change agenda in the banking sector.

Environmental impact assessment in microalgal lipid production: carbon footprint and net emissions

This study focuses on analyzing the role of microalgae in mitigating climate change through CO2 capture and lipid production, which can be used in the development of energy products and commercially relevant products. The objective was to evaluate the net CO2 emissions in three lipid production scenarios from microalgae, in addition to analyzing the impact of various biomass pretreatment technologies before lipid extraction. For this purpose, only the emissions directly generated by energy consumption in the process and the amount of CO2 that can be captured by microalgae cultivation were considered. In all three scenarios, CO2 capture during biomass cultivation and emissions associated with maintaining the process in operation were evaluated. The results show that the emissions generated by energy consumption were 3.56 kg-CO2/kg-oil, 2.19 kg-CO2/kg-oil, and 2.36 kg-CO2/kg-oil in scenarios 1, 2, and 3, respectively, while the CO2 emissions captured in microalgae cultivation were three to four times higher, ultimately resulting in negative emissions in all scenarios. The efficiency of CO2 capture per kilogram of oil produced varies between scenarios, suggesting that the choice of technology and process conditions significantly influence the overall environmental impact. This analysis identifies areas of opportunity to improve microalgal biomass utilization processes, highlighting the stages of the process with the greatest impact on the carbon footprint and enabling the comparison of different technologies on the same basis.

Synthetic natural gas (SNG) production by biomass gasification with CO2 capture: Techno-economic and life cycle analysis (LCA)

The integration of renewables with CCUS technologies has the promising potential to deliver energy applications with overall negative CO2 emissions which would significantly contribute to the climate neutrality. Moreover, the renewable-based synthetic fuels are predicted to replace the conventional fossil fuels. The current work evaluates key techno-economic and environmental indicators for the SNG production from various renewable fuels (e.g., sawdust, residual wood, organic wastes, agricultural and urban wastes etc.) through gasification process fitted with decarbonization capability. The investigated plant capacity was set to 500 MWth SNG with 60 % CO2 capture rate of primary fuel (biomass). The overall concept was evaluated using various process engineering approaches e.g., reactor & process modelling and simulation, model validation, heat and power analysis, techno-economic assessment combined with detailed environmental impact by Life Cycle Analysis (LCA). The investigated design shows promising performance indicators such as high cumulative energy efficiency (69 %) and carbon conversion to SNG, almost zero plant specific CO2 emissions (3 kg/MWh) and overall negative carbon emissions (−457 kg/MWh) from the whole biomass chain. The SNG production cost is not yet fully competitive versus the EU natural gas prices (53 vs. 30–35 €/MWh) but it shows promising potential considering the trends of increasing fossil prices and CO2 emission tax.

Bringing it all together: science priorities for improved understanding of Earth system change and to support international climate policy

Abstract. We review how the international modelling community, encompassing integrated assessment models, global and regional Earth system and climate models, and impact models, has worked together over the past few decades to advance understanding of Earth system change and its impacts on society and the environment and thereby support international climate policy. We go on to recommend a number of priority research areas for the coming decade, a timescale that encompasses a number of newly starting international modelling activities, as well as the IPCC Seventh Assessment Report (AR7) and the second UNFCCC Global Stocktake. Progress in these priority areas will significantly advance our understanding of Earth system change and its impacts, increasing the quality and utility of science support to climate policy. We emphasize the need for continued improvement in our understanding of, and ability to simulate, the coupled Earth system and the impacts of Earth system change. There is an urgent need to investigate plausible pathways and emission scenarios that realize the Paris climate targets – for example, pathways that overshoot 1.5 or 2 °C global warming, before returning to these levels at some later date. Earth system models need to be capable of thoroughly assessing such warming overshoots – in particular, the efficacy of mitigation measures, such as negative CO2 emissions, in reducing atmospheric CO2 and driving global cooling. An improved assessment of the long-term consequences of stabilizing climate at 1.5 or 2 °C above pre-industrial temperatures is also required. We recommend Earth system models run overshoot scenarios in CO2-emission mode to more fully represent coupled climate–carbon-cycle feedbacks and, wherever possible, interactively simulate other key Earth system phenomena at risk of rapid change during overshoot. Regional downscaling and impact models should use forcing data from these simulations, so impact and regional climate projections cover a more complete range of potential responses to a warming overshoot. An accurate simulation of the observed, historical record remains a fundamental requirement of models, as does accurate simulation of key metrics, such as the effective climate sensitivity and the transient climate response to cumulative carbon emissions. For adaptation, a key demand is improved guidance on potential changes in climate extremes and the modes of variability these extremes develop within. Such improvements will most likely be realized through a combination of increased model resolution, improvement of key model parameterizations, and enhanced representation of important Earth system processes, combined with targeted use of new artificial intelligence (AI) and machine learning (ML) techniques. We propose a deeper collaboration across such efforts over the coming decade. With respect to sampling future uncertainty, increased collaboration between approaches that emphasize large model ensembles and those focussed on statistical emulation is required. We recommend an increased focus on high-impact–low-likelihood (HILL) outcomes – in particular, the risk and consequences of exceeding critical tipping points during a warming overshoot and the potential impacts arising from this. For a comprehensive assessment of the impacts of Earth system change, including impacts arising directly as a result of climate mitigation actions, it is important that spatially detailed, disaggregated information used to generate future scenarios in integrated assessment models be available for use in impact models. Conversely, there is a need to develop methods that enable potential societal responses to projected Earth system change to be incorporated into scenario development. The new models, simulations, data, and scientific advances proposed in this article will not be possible without long-term development and maintenance of a robust, globally connected infrastructure ecosystem. This system must be easily accessible and useable by modelling communities across the world, allowing the global research community to be fully engaged in developing and delivering new scientific knowledge to support international climate policy.

Numerical study of a chemical looping combustion system: Effects of fuel type and particle size distributions on the operating performance

Chemical looping combustion (CLC) using biomass offers a promising pathway for achieving negative carbon emissions. However, the different properties of coal and biomass affect reaction performance, which has not been fully explored in the CLC system. Additionally, the effects of particle size distributions (PSDs) of solid fuels and oxygen carriers (OCs) are inadequately addressed. In this study, a 3D reactive model using the computational particle fluid dynamics (CPFD) method is developed to investigate the effects of PSDs of both solid fuels and oxygen carriers on operating performance with coal and biomass as fuels. Results indicate that the average residence time in FR of coal and biomass particles is 0.86 s and 0.68 s, respectively, but biomass outperforms coal in reaction efficiency. For coal-fueled CLC, the average residence time is 0.46 s for coal particles with diameters of 100–200 μm, whereas it reaches 0.86 s for coal diameters of 300–700 μm. However, the reaction performance is better with smaller coal sizes due to char gasification being the rate-limiting step. In comparison, for biomass-fueled CLC, the reaction efficiency remains consistent across various particle sizes under the specified conditions due to the rapid release of volatile components and the low content of char. Additionally, it is found that the OC conversion ratio is mainly determined by their residence time in the zones with relatively higher concentrations of the combustible gas in FR. Employing OCs with overly wide PSDs such as 300–800 μm can compromise the material seal above the AR, increase the risk of gas leakage and decrease the separation efficiency of the inertial separator.

Biochar carbon removal from residues in Germany—assessment from environmental and economic perspectives

Abstract The topic of biochar carbon removal (BCR), which refers to the pyrolysis of biomass, is increasingly being discussed as a potential solution for the long-term removal of carbon dioxide from the atmosphere. However, BCR technology assessments in Germany, which are used as the basis for strategic decision-making, are often limited to woody biomass as an input material and are based on old data. Consequently, this study focuses on BCR from forest residues, straw and sewage sludge and assesses its contribution to negative emissions under current techno-economic framework conditions. Using life cycle assessment and annuity method, as well as complementary stakeholder engagement formats, the study provides a comprehensive analysis of BCR pathways in Germany based on an empirical, up-to-date data basis. The results highlight the environmental advantages of BCR, particularly in reducing greenhouse gas emissions compared to the conventional treatment of residues. The economic feasibility of BCR is uncertain, with profitability dependent on plant scale, biomass type and the integration of energy co-products. Stakeholder insights underscore the necessity for supportive policies and investment in BCR technology to enhance scalability. This interdisciplinary approach enriches the discourse on BCR’s role in achieving carbon neutrality and offers a robust data foundation for future evaluations.

Life cycle assessment of carbon capture and utilisation as a negative emission technology: Recommendations and case study

Life cycle assessment of carbon capture and utilisation as a negative emission technology: Recommendations and case study

Acceptorless dehydrogenation of glycerol catalysed by Ir(III) complexes with carbohydrate‐functionalised ligands: a sweet pathway to produce hydrogen and lactic acid

Glycerol, a by‐product of biodiesel production, has gained prominence as a precious platform chemical. To enhance the economic viability of the biodiesel production process and address the surplus of glycerol production, it is essential to transform it into value‐added products. In this context, homogeneous catalysis offers a promising avenue for glycerol valorisation. In this study, we introduce a family of iridium complexes bearing picolineamidate ligands with glucose‐functionalised substituents as novel homogeneous catalysts for glycerol to hydrogen and lactic acid conversion. These complexes exhibit high activity (conversion up to 53.3%) and 99% selectivity after 24 hours of reaction (TOFMAX=159 h‐1, TON24h=2498). Notably, the reaction occurs under ambient air and at milder temperature conditions (120°C) compared to other catalysts. These efforts in glycerol valorisation contribute to reducing biodiesel production costs, increasing the competitiveness of biofuels against petroleum‐based liquid fuels, giving rise to H2, through a global process with negative carbon dioxide emission, and lactic acid utilizable, among other, as a monomer for the synthesis of biodegradable plastics.

Sustainable negative emissions in Europe: evaluating scenarios to meet carbon neutrality by 2050

Abstract Using the Pan-European TIMES-VTT model, we studied pathways for carbon neutrality by 2050 for 31 European countries by modelling a large portfolio of various terrestrial and technological carbon dioxide removal (CDR) strategies. Negative emission technologies and practices (NETPs) such as af-/reforestation, soil carbon sequestration, bioenergy with carbon capture and storage, direct air capture and storage, biochar, and enhanced weathering were considered. Three different storylines were created to describe the role of NETPs in varying future developments. The scenario storylines illustrate potential opportunities and constraints for large scale NETP implementation focusing on (1) optimistic technology development, (2) strict protection of planetary boundaries, and (3) increased self-sufficiency due to geopolitical risks associated with policy fragmentation. The results show that the demand for NETPs could be on a gigaton scale to reach carbon neutrality in Europe by 2050. As different countries have different opportunities to implement NETPs, none of the NETP options should be excluded from mitigation portfolios at this stage. The results also indicate the potential of NETPs in providing cost-effective solutions for achieving climate targets. On the other hand, stricter greenhouse gas emission reduction policies are needed to avoid over-reliance on CDR.

Ash Interaction with Two Cu-Based Magnetic Oxygen Carriers during Biomass Combustion by the Chemical Looping with Oxygen Uncoupling Process.

Chemical-looping combustion (CLC) stands out as a promising method for carbon capture and storage for the purpose of mitigating climate change. The process involves the conversion of fuel facilitated by an oxygen carrier, with the resulting CO2 inherently separated from other air components. Notably, when applied to biomass combustion this process offers a pathway to achieving negative CO2 emissions. However, a significant challenge for CLC, particularly in its application to biomass, is the management of interactions between ash and oxygen carriers. Biomass-derived ashes typically contain substantial quantities of reactive ash-forming substances, such as alkaline and alkali earth elements. These interactions can impact the performance and longevity of the oxygen carrier, necessitating careful consideration and mitigation strategies in CLC systems utilizing biomass feedstocks. This study examined the interaction between biomass ash components and two recently developed oxygen carriers, Cu30MnFekao7.5 and Cu30MnFe, during combustion in a 1.5 kWth continuous unit. Both oxygen carriers achieved 100% combustion efficiency and a CO2 capture efficiency of 95% at 900 °C. Although the copper in both oxygen carriers did not exhibit any noticeable interaction with ash components, the accumulative presence of potassium and magnesium in Cu30MnFekao7.5 was identified by inductively coupled plasma and scanning electron microscopy with energy dispersive X-ray analysis, indicating an increase in the amount of both elements in the particles after combustion operation. No problems of agglomeration or fluidization were observed in any of the experiments.

A rough set-based model for predicting soil greenhouse gases response to biochar

Biochar application to soil is a potential climate change mitigation strategy. In addition to long-term sequestration of the carbon content of the biochar itself, its application may reduce the emissions of other greenhouse gases (GHGs) from the soil. However, the reported effects of biochar application on soil GHG fluxes exhibit inconsistent results. Prediction of such effects is an important gap that needs to be addressed in biochar research. In this study, rule-based machine learning models were developed based on rough-set theory. Data from the literature were used to generate the rules for predicting the effects of biochar application on soil GHG (CO2, N2O, and CH4) fluxes. Four rule-based models for CO2 fluxes, two rule-based models for N2O fluxes, and three rule-based models for CH4 fluxes were developed. The validity of these models was assessed based on both statistical measures and mechanistic plausibility. The final rule-based models can guide the prediction of changes in soil GHG fluxes due to biochar application, and thus serve as a decision-support tool to maximize the benefits of biochar application as a negative emission technology (NET). In particular, mechanistically plausible rules were identified that predict triggers for GHG fluxes that can offset carbon sequestration gains. This knowledge allows biochar application to be calibrated to local conditions for maximum efficacy.Graphical

Tradeoffs between economy wide future net zero and net negative economy systems: The case of Chile

Given the possible economic consequences, poorer countries have more challenges in delivering their Nationally Determined Contributions. As a developing country, Chile has pledged to attain carbon neutrality by 2050. While Chile has implemented several mitigation measures, it still relies heavily on carbon sequestration, intending to sequester around 65 MtCO2e by 2050. However, heavy reliance on sequestration poses several risks as the literature shows that natural sinks, particularly forest and land, are exposed to severe impacts from global warming and climate change. Fortunately, Chile has significant renewable energy potential, which, if fully utilized, may move the country towards a net negative emissions context. To assess if such a net-negative system is feasible in the context of Chile, a new regional version of the Global Change Analysis Model for Chile is developed. The model is used to investigate the effects and required levels of investment in renewable energy and decarbonization of end-use sectors to achieve economy-wide net negative emissions scenarios. The design of net negative pathways follows a statistical approach based on the expected sequestration capacity in 2050 and its corresponding confidence interval. The results are compared to scenarios that are aligned with the objective of carbon neutrality by 2050. The findings show that obtaining net-zero emissions by 2050 is possible, however achieving net negative systems will be dependent on existing sequestration capacity and the application of economic incentives to boost green energy deployment in Chile as well as to push such green energy, in the form of electricity or e-fuels, into hard to decarbonize final demand sectors, such as transport, mining, and industry demand sectors. The results also indicate that after significantly reducing CO2 emissions from the energy sector (primarily the power sector), the agricultural sector and other urban and industrial sectors still contribute to non-significant levels of CH4 and N2O emissions.

Mild one-pot production of glycerol carbonate from CO2 with separation from ionic liquid catalyst

Carbon capture and utilization stands as way forward in the minimization of CO2 emissions. It complements the search for clean and effective energy, as it is challenging to achieve zero to negative CO2 net emissions. The glycerol carbonate product opens a new strategy based on a double-residue approach (glycerol and CO2) to contribute, together with ionic liquids (ILs), drafting a new one-pot concept (intensified three phase reactor) at mild conditions and using homogeneous catalysts. In this work, the catalytic activity of [P666,14][Br] in the cycloaddition of CO2 to glycidol has been demonstrated to be highly effective under mild conditions of 45 °C and 5 bar. In addition, liquid–liquid extraction approach is found to be an efficient separation strategy for carbonate product and IL catalyst. 1-Decanol (DOH) is selected as efficient extracting solvent, due to its almost complete immiscibility with glycerol carbonate, as well as the high distribution ratio of the IL catalyst in DOH rich phase. It implies an easy product separation and, simultaneously, an easy catalyst recovery. A preliminary kinetic validation of the three-phase reactor performance has been properly described, enabling the intensified concept. Finally, combining COSMO/Aspen simulation and life cycle assessment (LCA) methodologies, low energy consumption (avoiding heating) and low GWP scenarios for the CO2 conversion process have been concluded. This work enables a new concept together with concluding the path to developing this CCU technology in the search of zero to negative CO2 emissions to sustainably capture and convert CO2 into value-added products.

Study on the mechanism of competitive adsorption on the surface of potassium carbonate during direct air capture process

Direct air capture carbon dioxide (DAC) technology has the potential to achieve negative carbon emissions. Alkali metal-based absorbents (the active ingredient is mainly potassium carbonate or sodium carbonate) have a broad application prospect in DAC field. There is a paucity of reports on the competitive adsorption of major components of air on adsorbent surfaces. In this paper, the competitive adsorption behaviors of CO2, H2O, N2, and O2 on the surface of K2CO3 were investigated based on first principles and density functional theory (DFT), the synergic competition mechanism of each gas during adsorption was revealed by analyzing the parameters of adsorption energy, charge transfer, weak interactions and so on. The results showed that the maximum adsorption energy of CO2 by K2CO3 was 0.557 eV, and the relationship between the maximum adsorption energies of the four gases was O2 > H2O > CO2 > N2. The interaction between H2O and CO2 during co-adsorption inhibited their adsorption on the K2CO3 surface, especially weakening the adsorption effect of the surface O atoms on the H2O. Under CO2_N2_O2 gas composition, CO2 chemisorption occurred due to the strong oxidizing property of O2, the charge transfer effect commonly existed in the adsorption process of each gas, which contributed the most to O2 adsorption. The obtained results can further deepen the decarbonization mechanism of alkali metal-based adsorbents.

The cost of CO2 emissions abatement in a micro energy community in a Belgian context

This paper investigates and quantifies the benefits and the cost of CO2 emissions abatement of a Micro Energy Community (MEC) in a tiny residential cluster of three houses in a Belgian context. A simulation-based comparative analysis is performed of two individual and two MEC concepts, i.e. a reference scenario, an individual electrification scenario, an electricity sharing scenario, and an energy community scenario. A deterministic dynamic white-box modelling approach, including optimal control, is used, considering heat for space heating and domestic hot water, and electricity for electrical appliances. The energy system that achieves the greatest emission reduction at the lowest cost, has a collective heat pump and a photovoltaic installation sized based on the plug load demand. This system reduces the annual CO2 emissions by 11.48 tons at a cost of 179 EUR/ton CO2 considering 2021 dynamic retail electricity prices with a median of 251 EUR/MWh and a fixed retail gas price of 64 EUR/MWh. However, the results are strongly dependent on the gas-electricity price ratio. The highest value of the retail gas price in 2021 leads to a negative CO2 emissions abatement cost of 154 EUR/ton CO2, putting energy community concepts on the radar for a cost-effective energy transition.

Process Integration Technique for Targeting Carbon Credit Price Subsidy

Mitigating climate change requires a portfolio of strategies and the use of carbon dioxide removal techniques or negative emissions technologies (NETs) will be necessary to achieve to achieve this goal. However, the high implementation costs of advanced NETs lead to expensive carbon credits, hindering their broad acceptance and use. One potential solution involves governmental support through subsidies, aiming to boost the availability of NET-derived carbon credits. This research uses a graphical technique based on an extension of pinch analysis to identify the ideal subsidy level for carbon dioxide removal, taking into account factors such as carbon pricing, supply, and demand. The proposed approach modifies the limiting composite curve (LCC) methodology to accurately determine the optimal subsidy and establish the baseline amount of subsidized carbon dioxide removal needed. The approach enables the convenient and efficient construction of the LCC using a composite table algorithm. To illustrate the proposed methodology, two case studies composed of different NETs and demand sectors are investigated. The results show the most advantageous subsidy levels for these technologies, providing valuable insights to guide policymakers and investors in their decarbonization efforts. This research contributes to the development of effective governance and investment strategies by optimizing NET subsidy allocation. Such optimization is crucial for facilitating the widespread implementation of these technologies, which are in-line with the global efforts to mitigate climate change.

Advancing the deployment and information management of direct air capture: A solution enabled by integrating consortium blockchain system

Direct air capture (DAC) is a critical and emerging Negative Emissions Technology (NET) that directly removes CO2 from the atmosphere, significantly contributing to climate change. However, the deployment and management of large-scale DAC faces challenges such as collections and analysis of energy consumption data, intricate device and system management, emission prediction and operation strategy, precise carbon footprint tracking, etc. This paper proposes the integration of blockchain technology with DAC systems to address these challenges, utilizing blockchain's inherent properties of immutability, security, and transparency. The implementation strategy includes the development of a DAC consortium blockchain system, leveraging a consensus mechanism11Consensus mechanism: The programming and process used in blockchain systems to achieve distributed agreement about the ledger's state or the state of a data set. (Source: Investopedia), ECDSA encryption22Elliptic Curve Digital Signature Algorithm (ECDSA): In cryptography, the Elliptic Curve Digital Signature Algorithm (ECDSA) offers a variant of the Digital Signature Algorithm (DSA) which uses elliptic-curve cryptography. As with elliptic-curve cryptography in general, the bit size of the private key believed to be needed for ECDSA is about twice the size of the security level, in bits. (Source: Wikipedia), IoT33Internet of things (IoT): describes devices with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other communication networks. (Source: Wikipedia) integration, and digital signatures. Preliminary modeling of the proposed system suggests potential improvements in operational efficiency and a reduction in data inaccuracies. The proposed system underscores the system's ability to streamline identity verification, improve data collection accuracy, and facilitate secure, confidential information sharing among DAC stakeholders. By enhancing the efficiency and reliability of DAC operations, this approach supports the scalable and effective deployment of NETs in the global effort to combat climate change. Future research will focus on empirical validation through pilot projects and simulations to further substantiate these claims.

Power generation with negative CO2 emissions through bio-electricity with CCS using dry co-gasification of coal-biomass blends

Power generation with negative CO2 emissions through bio-electricity with CCS using dry co-gasification of coal-biomass blends

Modeling biomimetic absorbent compounds for capturing carbon dioxide

Carbon capture and storage is a critical component of negative emission technologies for achieving economy-wide carbon neutrality to mitigate climate change and limit global temperature increase. Removal of CO2 can be undertaken after the standard pollution controls. Yet, the separation of CO2 from flue gas via CO2 capture processes is challenging because a high volume of gas must be treated, the CO2 is dilute, the flue gas is at atmospheric pressure, trace impurities can degrade capture media, and the captured CO2 must be compressed. We present a computational study of a novel family of biomimetic materials for such carbon capture processes based on the Crassulacean Acid Metabolism. Phosphoenolpyruvate serves as a template for designing similar molecules for use as CO2 solvents with designed thermochemical properties.