Weekly CDR Publication Highlights (6 February 2025)
This week’s publications cover a wide range of topics such as the meteorologic conditions that emerge in West Africa under various carbon dioxide removal scenarios, direct air capture, ocean alkalinity enhancements, biochar carbon dioxide removal and bioenergy with carbon capture and storage.
Projected Heat/Cold Waves and Heat Stress Conditions in West Africa under Carbon Dioxide Removal Scenarios
Abstract
Climate change is a global concern and global efforts are being made to reduce the presence of carbon dioxide in the atmosphere. This study investigated carbon dioxide removal impact on heat/cold waves and heat stress conditions in West Africa using UKESM1 and CNRM-ESM1-C1 Carbon Dioxide Removal Model Intercomparison Project (CDRMIP) simulation outputs. Understanding this impact is important due to the region’s vulnerability to climate change and its dependence on climate-sensitive sectors such as agriculture and public health. Three indices – Effective Temperature Index (ETI), Humidex Index (HD) and Temperature Humidity Index (THI) were used to evaluate heat stress in each of the periods – 1990–2019 (reference), 2040–2069, 2070–2099 and 2100–2129 since they have humidity term and hence, can give a comprehensive description of the climate scenario over West Africa. Excess heat factor (EHF) index was used to evaluate heat/cold wave. The three indices projected heat stress over West Africa within thermal comfort limit. 80.3% of the total number of days analyzed in Sahel regions were within the range of normal days. On the average, 7665 normal days were projected over West Africa at 95th and 5th percentile daily mean temperatures (reference period) of 39.2°C and 25.3°C, respectively, in the period 2070-2099. There were 3135 cold days with no “severe” intensity. The analyses revealed predominance of cold wave and reduction in daily mean temperature before the end of 21st century, indicating the potentials of CDR in ameliorating the prevailing heatwave over West Africa.
Uzoma, E. K. and Adeniyi, M.O. (2025) 11 (112) Projected Heat/Cold Waves and Heat Stress Conditions in West Africa under Carbon Dioxide Removal Scenarios. Modeling Earth Systems and Environment.
Read the full paper here: Projected Heat/Cold Waves and Heat Stress Conditions in West Africa under Carbon Dioxide Removal Scenarios I Modeling Earth Systems and Environment.
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Advancements and Challenges in Direct Air Capture Technologies: Energy Intensity, Novel Methods, Economics and Location Strategies
Abstract
Direct air capture (DAC) technology is increasingly recognized as a key tool in the pursuit of climate neutrality, enabling the removal of carbon dioxide directly from the atmosphere. Despite its potential, DAC remains in the early stages of development, with most installations limited to pilot or demonstration units. The main barriers to its widespread implementation include high energy demands and significant capture costs. This literature review addresses the most critical research directions related to the development of this technology, focusing on its challenges and prospects for deployment. Particular attention is given to studies aimed at developing new, cost-effective, and efficient sorbents that could significantly reduce the energy intensity and costs of the process. Alternative technologies, such as electrochemical and membrane-based processes, show promise but require further research to overcome limitations, such as sensitivity to oxygen presence or insufficient membrane selectivity. The economic feasibility of DAC remains uncertain, with current estimates subject to significant uncertainty. Governmental and regulatory support will be crucial for the technology’s success. Furthermore, the location of DAC installations should consider factors such as energy availability, options for carbon dioxide storage or utilization, and climatic conditions, which significantly affect process efficiency. This review highlights the necessity for continued research to overcome existing barriers and fully harness the potential of DAC technology.
Kotowicz, J., Niesporek, K. and Baszczénska, O. (2025) 18 (3) Advancements and Challenges in Direct Air Capture Technologies: Energy Intensity, Novel Methods, Economics and Location Strategies. Energy Management: Economic, Social, and Ecological Aspects.
Read the full paper here: Advancements and Challenges in Direct Air Capture Technologies: Energy Intensity, Novel Methods, Economics and Location Strategies I Energy Management: Economic, Social, and Ecological Aspects.
Efficiency Metrics for Ocean Alkalinity Enhancements under Responsive and Prescribed Atmospheric pCO2 Conditions
Abstract
Ocean alkalinity enhancement (OAE) and direct ocean removal (DOR) are emerging as promising technologies for enacting negative emissions. The long equilibration timescales, potential for premature subduction of surface water parcels, and extensive horizontal transport and dilution of added alkalinity make direct experimental measurement of induced CO2 uptake challenging. Therefore, the challenge of measurement, reporting, and verification (MRV) will rely to a great extent on general circulation models, parameterized and constrained by experimental measurements. A number of recent studies have assessed the efficiency of OAE using different model setups and different metrics. Some models use prescribed atmospheric CO2 levels, while others use fully coupled Earth system models. The former ignores atmospheric feedback effects, while the latter explicitly models them. In this paper it is shown that, even for very small OAE deployments, which do not substantially change atmospheric pCO2, the change in oceanic CO2 inventories differs significantly between these methods due to atmospheric feedback causing some ocean CO2 off-gassing. An analogous off-gassing occurs during direct air capture (DAC). Due to these feedback effects, care must be taken to compute the correct metrics when assessing OAE efficiency with respect to determining negative emissions credits, as opposed to determining the effect on global temperatures. This paper examines the commonly used metrics of OAE efficiency, their exact physical meanings, the assumptions inherent in their use, and the relationship between them. It is shown that the efficiency metric η(t), used in prescribed pCO simulations, equals the equivalent schedule of a gradual DAC removal and storage in a fully coupled system.
Tyka, M. (2025) 22 (1) Efficiency Metrics for Ocean Alkalinity Enhancements under Responsive and Prescribed Atmospheric pCO2 Conditions. Biogeosciences.
Read the full paper here: Efficiency Metrics for Ocean Alkalinity Enhancements under Responsive and Prescribed Atmospheric pCO2 Conditions I Biogeosciences.
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Do Oversimplified Durability Metrics Undervalue Biochar Carbon Dioxide Removal?
Abstract
Soil amendment of biochar—the solid product of biomass pyrolysis—is one of few engineered strategies capable of delivering carbon dioxide removal (CDR) today. Quantifying CDR for biochar projects hinges critically on the durability of biochar materials once amended in soil. However, consensus on the definition of durability is still evolving, and as a result, standards developing organizations have generated a variety of different methodologies to assess the removal value of biochar projects. These methodologies primarily rely on single-parameter regression models to link the molar H/C ratio—an easily measurable bulk chemical metric—to the modeled durability of biochar materials. Specific deployment variables are not commonly considered. Thus, although H/C-based methodologies simplify project development and CDR assessment, questions remain as to how well they predict real project outcomes. Via a re-analysis of existing biochar incubation data and several case studies, we show that durability standards based on bulk compositional metrics are biased towards particular feedstocks and may not account for key environmental drivers. Without provisions for these factors, we find that existing assessment models appear to discount the removal value of biochar projects significantly. However, our conclusions rely on predictive models with important weaknesses and unknown uncertainty—pointing to a need to develop a use-aligned database. Limitations notwithstanding, our findings ultimately suggest the biochar ``durability problem’’ may be an artifact of the desire to simplistically define it. To reliably credit CDR, we propose a series of recommendations, including the creation of representative distributions for current feedstocks and environmental gradients to better align experimental data with real-world practices. Further, we suggest an approach to integrate in-field measurement protocols with existing strategies to evaluate CDR value, with potential to co-generate data to guide deployment, maximize agronomic co-benefits, and improve confidence in project integrity.
Ringsby, A. and Maher, K. (2025) Do Oversimplified Durability Metrics Undervalue Biochar Carbon Dioxide Removal? Environmental Research Letters.
Read the full paper here: Do Oversimplified Durability Metrics Undervalue Biochar Carbon Dioxide Removal? I Environmental Research Letters.
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Bioenergy with Carbon Capture and Storage Technology to Achieve Net Zero Emissions - A Review
Abstract
Bioenergy with carbon capture and sequestration (BECCS) technology has emerged as a flourishing and advanced approach for capturing CO2 since it promotes clean energy, supports sustainable resource management, advances environmental sustainability and negative emissions. Thus, this novel comprehensive review thoroughly explores the contribution of biomass oxy-fuel technology in capturing CO2 and achieving net zero emissions. Furthermore, the review meticulously addresses pollution emissions and ash-related issues along with control strategies in the fluidized bed oxy-fuel configuration, providing in-depth insights into scale-up feasibility and techno-economic and environmental analysis. Remarkably, oxy-fuel combustion (OFC) achieves CO2 recovery rates of up to 96.24%, with around 70% of flue gas recirculated following biomass combustion. Increased biomass raises CO levels, especially above 30%, with rapid conversion to CO2 at 100% O2. Under oxy-fuel conditions, NOx and SOx emissions are reduced by utilizing effective strategies like gas and oxygen staging and limestone injection for desulfurization. Combustion produces fly ash with minerals and heavy metals, causing boiler fouling, while PM1 contains K, Cl, P, S and Na, and PM1-10 includes Mg, Ca and Si. Furthermore, 1% NH4Cl-modified biomass char effectively removes mercury. Globally, there are 20 BECCS projects spanning various methods and fuels. Additionally, oxy-fuel process scored 10/10 for both global warning potential and acidification pollution, indicating minimal emissions. It may become more financially viable than fossil fuels with a carbon tax exceeding $28.3 per tonne of CO2. BECCS has reached TRL 7 in the industry, with CO2 capture costs ranging from $40 to $120 per ton, offering a cost advantage over other technologies.
Sher F. et al. (2025) 210 Bioenergy with Carbon Capture and Storage Technology to Achieve Net Zero Emissions - A Review. Renewable and Sustainable Energy Reviews.
Read the full paper here: Bioenergy with Carbon Capture and Storage Technology to Achieve Net Zero Emissions - A Review I Renewable and Sustainable Energy Reviews.