There are a wide variety of CDR approaches, ranging from the conventional, like reforestation and ecosystem restoration, to the more novel, like Direct Air Capture with CCS, Enhanced Rock Weathering, and Ocean Alkalinity Enhancement, which have yet to be proven at scale. We welcome contributions that highlight critical aspects of the use of CDR approaches in climate mitigation strategies with a focus on the potential and co-benefits of different methods at various scales, sustainability limits and feasibility of different options in portfolios of approaches, and the risks of different strategies - either to people, the environment, or of CO2 rerelease due to loss of durable storage or other sustainability goals. Contributions that touch on societal aspects in particular CDR policies and governance, including the impact of carbon markets and the ability to Monitor, Report, and Verify (MRV) removals are also encouraged.
We invite a broad range of approaches and perspectives, spanning studies using fully coupled Earth System Models (ESMs), Integrated Assessment Models (IAMs), as well as economic and social science methods.
Orals: Tue, 5 May, 08:30–15:45 | Room 0.49/50
The Intergovernmental Panel on Climate Change (IPCC) has clearly stated that carbon dioxide removal (CDR) must happen in parallel with CO2 emissions reductions, and the giga-tonne scale of CDR that is needed will only become a reality if storage in the oceans is seriously considered. One such marine CDR (mCDR) approach is ocean iron fertilization (OIF), which harnesses carbon drawdown by phytoplankton in areas of the ocean where growth is limited by iron availability. A new generation is poised to build on the rich history of prior OIF research with parallel objectives of i) addressing knowledge gaps and uncertainties regarding the additionality and durability of OIF mCDR; and ii) fully evaluating the ecological and environmental impacts of iron addition. To ensure these new field trials are carried out in a transparent and responsible manner with the appropriate guardrails, they must be developed and conducted in collaboration with social scientists, governance experts, and in consultation with interested communities. The Exploring Ocean Iron Solutions (ExOIS) consortium is a multidisciplinary group of researchers focused on exploring OIF through natural science, social science, and governance lenses to contribute to our growing understanding of how mCDR may be responsibly used to combat the climate crisis. https://oceaniron.org/
How to cite: Morris, P., Buesseler, K., Chai, F., Drysdale, J., Ramakrishna, K., Roche, K., Smith, S., Wells, M., and Yoon, J.-E.: Dusting the rust off ocean iron fertilization research studies for mCDR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15868, https://doi.org/10.5194/egusphere-egu26-15868, 2026.
The depth-dependent, volume-integrated pH of seawater over can be measured directly from the profiles of ambient noise using passive acoustic absorption spectroscopy. Acoustic absorption in seawater is frequency dependent and caused by the chemical relaxation of three constituents in the band 1 – 10 kHz: boric acid and magnesium carbonate below 3 kHz and magnesium sulfate above 3 kHz. The concentrations of boric acid and magnesium carbonate are directly tied to seawater pH, while the concentration of magnesium sulfate is not, causing the wideband acoustic absorption curve to be sensitive to pH. Under strong local wind conditions, ambient noise is dominated by locally generated surface noise caused by wind-driven breaking of surface gravity waves. This noise field has been shown to have a depth-independent directionality and weak frequency and depth-dependent intensity. However, comparisons of the depth-dependent frequency changes of the ambient noise spectrum to an analytical model can be used to infer the depth-integrated pH. This sensing method has been demonstrated using wideband (5 Hz – 30 kHz) vertical ambient sound profiles recorded using free-falling acoustic recording platforms that have been deployed in the Philippine Sea, Mariana Trench, and Tonga Trench from 2009 to 2021. These recorders capture the ambient noise field the surface to depth up to 10 km, along with direct measurements of temperature, salinity, pressure, and sound speed. Estimates of pH were found by minimizing the mean absolute percent error between the measurements and an analytical model of the depth-dependence of ambient noise. This method of passive acoustic absorption spectroscopy demonstrates the potential and sources of uncertainty in determining the depth-averaged value of pH. The method could be suitable for the long-term passive acoustic monitoring of ocean acidity.
How to cite: Barclay, D., Uzhansky, E., and Buckingham, M.: Measuring ocean pH with ambient noise, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12879, https://doi.org/10.5194/egusphere-egu26-12879, 2026.
Ocean alkalinization using a pH-equilibrated bicarbonate-enriched solution was evaluated at the mesoscale to investigate the long-term stability of carbon stored as dissolved bicarbonate in seawater. A treated solution was produced by reacting Ca(OH)2 with CO2 in natural seawater and adjusting the pH to match ambient conditions. This solution was introduced into mesocosms, increasing the dissolved inorganic carbon (DIC) content 250 to 1990 µmol C/L above natural levels. The stability of chemical parameters in the mesocosms was monitored over a 76-day period. Under moderate alkalinization (≤1000 µmol C/L of added DIC), more than 90% of the added inorganic carbon remained stable for nearly two months. In contrast, treatments leading to an aragonite saturation state (ΩAr) exceeding 10, exhibited rapid declines in stability due to secondary carbonate precipitation and CO2 degassing, particularly at high temperatures. Although natural seawater salinity and pH did not independently induce instability, both parameters significantly influenced the carbonate supersaturation state and therefore the system’s sensitivity to precipitation and degassing. Seasonal variations in seawater temperature, salinity, and pH were found to strongly modulate theoretical ΩAr and should be incorporated into dosing strategies and site-selection criteria for ocean alkalinization. These results highlight the importance of real-time, site-specific seawater characterization for the safe and effective deployment of alkalinity enhanced carbon storage.
How to cite: Jamali Alamooti, S., Comazzi, F., Kratter Thaler, E., Groppelli, S., Calvi, D., Raos, G., and Macchi, P.: pH-Equilibrated Ocean Alkalinization: Mesoscale Evaluation of Long-Term Stability , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1491, https://doi.org/10.5194/egusphere-egu26-1491, 2026.
Potential influence of applying glacial rock flour for stimulating primary production for marine carbon dioxide removal.
Jørgen Bendtsen1,2, Niels Daugbjerg3, Kristina Vallentin Larsen1
1Centre for Rock Flour Research, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark
2ClimateLab, Symbion Science Park, Fruebjergvej 3, DK-2100 Copenhagen Ø, Denmark
3Department of Biology, University of Copenhagen, Universitetsparken 4, DK-2100 Copenhagen Ø, Denmark
Glacial rock flour (GRF) is a fine-grained silicate mineral that is transported to the coastal ocean by meltwater rivers and subglacial discharge from the Greenland Ice Sheet. It is formed below glaciers when they abrade the bedrock to a fine powder, and it is available in very large quantities in sedimentary deposits. GRF has typically a median grain-size of ~2-5 µm, and it contains essential nutrients and trace metals for phytoplankton growth. The fine grain size results in residence times of suspended GRF in the surface layer of the order of days or weeks, and furthermore implies a relatively large reactivity due to its large surface area. The long residence time allows phytoplankton and marine microbiomes to exploit nutrients released by silicate hydrolysis or to directly interact and mobilize macro-nutrients (i.e., P, Si) and trace metals (e.g., iron) from the GRF. These characteristics, and the fact that GRF constitute a natural source of elements to the ocean, makes the material potentially relevant for marine carbon dioxide removal (mCDR). Here we analyse the potential impacts of dispersing GRF in the ocean on phytoplankton growth and biogeochemical cycling by implementing critical parameters of mobilisation rates of bioavailable nutrients and trace metals from GRF in a 1-dimensional model of the water column. Previous studies have demonstrated a positive effect of GRF on the growth rates of phytoplankton, however, the actual compounds that stimulates the growth is poorly known. Results from our incubation experiments show that iron, manganese and phosphorus can be mobilized from GRF and support an exponential growth of a subpolar green alga. We also estimate the potential maximum amount of iron that can be extracted from the GRF. These critical parameters are implemented in the model and the potential impact on CO2-uptake, primary production, biogeochemical cycling, chlorophyll a and light of dispersing GRF in iron-depleted areas are simulated. The dose-response relationship between GRF-dispersal and impact on surface chlorophyll, pCO2 and oxygen are analysed in relation to monitoring the efficacy of mCDR.
How to cite: Bendtsen, J., Daugbjerg, N., and Larsen, K. V.: Potential influence of applying glacial rock flour for stimulating primary production for marine carbon dioxide removal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18638, https://doi.org/10.5194/egusphere-egu26-18638, 2026.
Bioenergy plantations are frequently proposed as a cornerstone of carbon dioxide removal (CDR) portfolios, yet their long-term productivity relies on nutrient availability. Environmental impacts with fertilizer use and finite supply of phosphate rock raise sustainability and geopolitical concerns. Here, we combine global yield observations with a process-based land surface model to assess the role of nutrient limitations in Eucalyptus plantations under repeated harvest cycles and to evaluate whether enhanced rock weathering (ERW) using basalt can alleviate P constraints while delivering additional CDR.
Using idealized global simulations with ORCHIDEE-CNP, we vary nitrogen (N) and P inputs to quantify yield responses and fertilizer requirements. We show that in (sub)tropical regions, high biomass yields cannot be achieved without substantial P additions due to strongly weathered, nutrient-poor soils. In the absence of fertilization, yields decline in most regions over successive rotations as P is progressively exported with harvested biomass. We further compare costs related to conventional and alternative P supply strategies. Increasing carbon prices substantially improve the competitiveness of basalt as a P source, as revenues from associated CO₂ removal from ERW can offset life-cycle costs. At carbon prices above 200 USD tCO₂⁻¹, basalt-derived P could become cost-neutral. At these prices, basalt provides a cost-efficient and widely available P source with lower eutrophication risks compared to conventional fertilized and potential co-benefits for soil carbon storage and ecosystem functioning..
Our findings (1) highlight systematic overestimations of large-scale bioenergy potentials in assessments that neglect soil fertility dynamics and (2) suggest that ERW could mitigate a key nutrient bottleneck for tropical bioenergy systems while enhancing the durability and sustainability of biomass-based CDR pathways, linking nutrient management directly to climate policy design.
How to cite: Goll, D. S., He, X., Li, W., Huang, Y., Martinez-Cano, I., Ciais, P., Fayad, I., and Tanaka, K.: The phosphorus bottleneck in bioenergy-based CDR – and how enhanced rock weathering could break it, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5521, https://doi.org/10.5194/egusphere-egu26-5521, 2026.
Enhanced rock weathering (ERW) is a carbon dioxide removal (CDR) strategy involving spreading silicate rock powder on croplands to speed up the natural weathering process, whereby CO2 reacts with rainwater and silicate minerals to form bicarbonate ions, which are eventually transported to and stored in the ocean. While ERW can potentially sequester gigatons of CO2 per year and therefore help achieve the Paris Agreement goal of limiting global warming to well below 2 °C, the biogeophysical effects of cropland soil amendment are possibly significant yet poorly constrained. For example, decreased soil albedo from spreading dark rock powder (e.g. basalt) on croplands might counteract cooling from CO2 drawdown. On the other hand, light rocks such as wollastonite skarn might enhance cooling by increasing soil albedo. Here we investigate temperature outcomes of various ERW deployment scenarios with an Earth system climate model of intermediate complexity (the UVic ESCM) constrained by albedo values measured from soil amended with varying amounts and types of rock powder. We find that, with aggressive application rates of 25 or 50 tonnes of rock dust per hectare on global cropland, ERW-induced cooling is slightly counteracted by ~5% with basalt and enhanced by ~20% with wollastonite. At basalt application rates of 10 tonnes ha-1 or below, changes to soil albedo and thus temperature outcomes are negligible. Our results demonstrate that non-CO2 effects of CDR deployment strategies should be considered in order to meet temperature goals while also informing best practices for ERW deployment with respect to minimizing cooling offset or maximizing cooling enhancement due to soil albedo modification.
How to cite: Dove, I., Spence, J., Wilson, S., and Zickfeld, K.: Temperature outcomes of enhanced rock weathering deployment scenarios constrained by soil albedo measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5945, https://doi.org/10.5194/egusphere-egu26-5945, 2026.
The combined application of pyrogenic carbon (biochar) and silicate rock minerals (Enhanced Rock Weathering, or ERW) represents a promising integrated strategy for carbon dioxide removal (CDR). However, the effectiveness of these measures is governed by site-specific interactions among soil physical properties, microbial activity, and vegetation processes. To address this challenge, we developed LiDELS (LiBry–DETECT Layer Scheme), a process-based one-dimensional ecosystem model that couples vertical soil water and energy dynamics with vegetation carbon assimilation, soil CO2 production and transport, and drivers of mineral weathering.
Initial validation and millennial-scale simulations for a sandy soil profile under temperate climate conditions indicate that co-application effects are locally dominated by biochar. Solo biochar application produces the largest and most persistent increases in total and non-pyrogenic soil organic carbon (SOC) and sustains a moderate net CO2 sink over 1,000 years. In contrast, silicate rock (basanite) application alone yields only a small additional inorganic CDR flux via Ca2+ leaching, without substantially improving net ecosystem exchange (NEE) relative to the Control. Co-application of biochar and basanite and the use of rock-enhanced biochar (co-pyrolysed biomass with basanite) lead to intermediate trajectories in SOC and NEE that clearly exceed those of basanite alone, but do not surpass the CDR efficiency of sole biochar, even when evaluated over millennial timescales. These results suggest that in temperate, water-limited, coarse-textured soils, CDR benefits are primarily driven by organic carbon pathways and their positive feedbacks on vegetation productivity. The relative contribution of inorganic CDR pathways is expected to increase under warmer and more humid climatic conditions, where mineral weathering and bicarbonate export are accelerated.
Building on these site-scale results, ongoing work focuses on upscaling LiDELS to identify regional CDR “hotspots” and find which combinations of soil properties, mineralogy, and climate maximize amendment efficiency.
How to cite: Maslouski, M. and Porada, P.: Carbon dioxide removal through biochar and enhanced weathering: towards a scalable process-based modelling approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10975, https://doi.org/10.5194/egusphere-egu26-10975, 2026.
- Tesfa1,2*, R. Todor1, M. Carrier1, S. Dubos1, M. Peyre-Lavigne1, L. Shirokova2, M. Sperandio1, L. Menjot, A. Karen O.S. Pokrovsky2, C. Dumas1
1 TBI, Université de Toulouse, CNRS, INRAE, INSA Toulouse, France.
2 Géosciences Environnement Toulouse (GET) – Research Institute for Development [IRD]: Toulouse University, CNRS, Toulouse, France
*Corresponding author: marawittesfa.research@yahoo.com
To reduce atmospheric carbon (CO2) level, the presented study aims to understand the biological processes that entrap CO2 by calcium carbonate precipitation (CaCO3). Two biological mechanisms precipitating carbonates occur naturally [1]: (i) an active mechanism, where bacteria precipitate carbonates thanks to their metabolism and (ii) a passive mechanism, where microorganisms change the chemical environment by increasing the pH and/or producing exopolymers, sequentially inducing precipitation. In the presented study, the precipitation induced by anoxygenic phototrophic sulfur bacteria (APSB) was studied, pure cultures of Allochromatium Vinosum as a model microorganism.
To understand this biologically induced precipitation, we attempted to reproduce the chemical environment in a lab-controlled reactor which allowed to characterize the nature of precipitated minerals, quantify their yield and rates of formation to deduce their carbon capturing capacities. These experiments were conducted in small batch and semi-continuous bioreactors, containing A. Vinosum with its inorganic growth media (vitamins, trace elements, inorganic energy source, sodium carbonates and chloride calcium). The growth media was a strictly inorganic substrate to prevent heterotrophy. To optimize carbonate precipitation and pinpoint its driving variables, some parameters such as the concentration of bacteria, elements from the growth media (Sulfate, phosphate, Magnesium) and the incubation time were modified. The chemical environment was then monitored (pH, COD, inorganic carbon, ions…) and precipitates were collected subsequently to filtration, weighted and analyzed (XRD, SEM).
The incubation variation time displayed two different precipitation phases: rapid, reaching chemical equilibria within one hour, and slow, reaching equilibria within 15 days.
We hypothesize the rapid kinetics was chemically driven and the slow kinetics depended on A. Vinosum growth cycle. The presence of phosphate was also shown to induce calcium phosphate precipitation as apatite, competing with CaCO3 precipitation. Previous studies showed that CaCO3 precipitation occurs when bacteria have an organic energy source [2]. Because the aim here is to reduce CO2, by working in an inorganic growth media to precipitate carbonates with solely inorganic carbon sources, CaCO3 precipitation was challenging and the yields of carbonate precipitation were lower than in traditional experiments with organic-rich media. Improving the seal on the air tight bioreactors resulted in a better CaCO3 precipitation yield. The work in progress aim to optimize the precipitation and consequently CO2 capture by decoupling bacterial growth phase from the mineral precipitation phase by working with separate reactors.
[1] Dupraz, C., Visscher, P.T., 2005. Trends Microbiol. 13, 429–438.
[2] Bundeleva, I.A., Shirokova, L.S., Bénézeth, P., Pokrovsky, O.S., Kompantseva, E.I., Balor, S., 2012. Chem. Geol. 291, 116–131.
How to cite: Tesfa, M.: Capture of carbon dioxide by biologically induced precipitationof calcium carbonates by anoxygenic phototrophic sulfur bacteria, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1815, https://doi.org/10.5194/egusphere-egu26-1815, 2026.
It becomes hopeful to limit climate warming to 1.5 °C if woody debris produced in managed forests, metropolitan areas, orchards, and fire-prone forest lands over the globe is buried in deep soil. We have recently estimated that deep soil burying of woody debris produced in managed forests has the capacity to remove 10.1-12.3 Gt CO2 yr-1 from the atmosphere and slow down climate warming by 0.35 - 0.42°C by the end of this century. Similarly, waste wood materials from metropolitan areas, pruned woody materials from orchards, and woody materials from forest thinning or dead wood salvaged from forestry in fire-prone regions can be buried in deep soil for carbon dioxide removal (CDR) from the atmosphere. Globally, wildfire burning releases 7.7 ± 0.7 Gt CO2 yr-1 to the atmosphere. Urban woody waste is produced from pruned branches and fallen trees from streets and public areas, possibly in a range of 1-2 Gt CO2 yr-1. Taking all together, burying woody debris has the potential to remove substantially more than 12 Gt CO2 yr-1, which is approximately 10 times more effective than almost any of the other CDR methods that have been explored by the scientific community. For example, CDR methods, such as cover cropping, soil carbon sequestration, and enhanced rock weathering, have potentials to remove 1 Gt CO2 yr-1 or less. Forestation, which has been considered to have the largest CDR potential, may remove 1.54 Gt CO2 yr-1 according to a recent study. Even so, CDR via reforestation may no longer be effective once the past disturbed ecosystems have mostly been restored whereas burying woody debris can keep removing CO2 as woody debris can be sustainably delivered year after year. Moreover, burying woody debris costs the least in comparison with other CDR methods. Overall, deep soil burying of woody debris not only makes it hopeful to limit climate warming to 1.5 °C but also create markets for low-value timber common, reduce forest wildfire risks, and offer alternative practices for waste wood management in urban areas.
How to cite: Luo, Y.: Deep soil burying of woody debris as the most effective, least expensive, and most sustainable carbon dioxide removal strategy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7414, https://doi.org/10.5194/egusphere-egu26-7414, 2026.
As one of the world largest waste streams, cement-based construction materials offer a potentially scalable pathway for CO2 removal (CDR) through aqueous mineral carbonation, yet their efficiency and practical constraints remain poorly characterized. Here, we conducted controlled experiments to quantify CO2 capture by cement-based materials in aqueous conditions, tracking changes in headspace CO2, aqueous compositions, and CaCO3 formation. Headspace CO2 declined rapidly during carbonation, with the conversion to CaCO3 reaching up to 70% of the solid material within days. Reaction process was influenced by particle size, with finer materials sustaining CO2 uptake over longer periods due to higher reactive surface area. Based on the observed CO2 capture efficiency, applying carbonation to construction-waste streams globally could potentially sequester CO2 at the million tonnes scale annually. These findings demonstrate the practical potential of aqueous CO2 capture by construction waste, and highlight opportunities to integrate this pathway into managed environmental systems, such as water and agricultural infrastructures, within broader CDR application.
How to cite: Wu, W., Tai, Y.-H., Smith, S., and Van Cappellen, P.: Carbon Dioxide Removal by Construction Waste: Experimental Assessment of CO2 Capture Efficiency, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14134, https://doi.org/10.5194/egusphere-egu26-14134, 2026.
To meet the Paris Agreement targets we need large-scale deployment of carbon dioxide removal (CDR). Most of the literature focuses on the removal potential of CDR and the direct effect on temperature. Nevertheless, to design sustainable and robust mitigation strategies, we need to explore and quantify broader impacts of CDR on the Earth system. Although these effects on the Earth system have been identified, there is no comprehensive understanding of their magnitude if CDR is implemented on a large scale. The Planetary Boundary (PB) framework aims to maintain a safe operating system for humans. The PB framework, used with an Earth system model, could be used to systematically assess the positive or negative effects of different CDR methods on the Earth system features that are critical to human welfare.
We use the University of Victoria Earth System Climate Model (UVic ESCM) to simulate large-scale ocean alkalinity enhancement (OAE), artificial upwelling (AU), reforestation (REF), and bioenergy with carbon capture and storage (BECCS), under the SSP1-2.6 control scenario. Our goal is to assess the efficiency and sustainability of the selected CDR methods. Therefore, we use the PB framework to quantify CDR’s impact on the PBs of climate change, ocean acidification, land system change, biochemical flows, freshwater change, and biosphere integrity. By doing so, we can assess whether, after implementing CDR, the PB control variables stay below the boundaries (safe operating space) or go beyond it to the increasing or high-risk zone.
Our preliminary results show the impacts of OAE and REF on radiative forcing, CO2 concentration, ocean acidification, and land system change. In all the future scenarios, the radiative forcing level falls in the high-risk zone (3.00 Wm-2). In 2300, OAE and REF reduce the radiative forcing to 1.7 Wm-2, which gets closer to the upper end of the zone of increasing risk (1.5 Wm-2), but still in the high-risk zone. In 2100, the CO2 concentration decreases in all the future scenarios, getting closer to the upper end of the zone of increasing risk (450 ppm), only reached by REF. In 2300, the CO2 concentration further decreases, falling within the zone of increasing risk, with OAE and REF CO2 concentration of 383 and 387 ppm, respectively. REF almost reaches the PI forest coverage (92% in 2100, 96% in 2300), while OAE has a negligible impact on the land system change, staying, nevertheless, within the PB (75% of PI forest coverage). OAE has the highest impact on ocean acidification, quantified as surface ocean saturation state with respect to aragonite (Ωarag). OAE increases the surface ocean’s aragonite saturation state (2.63 Ωarag) close to the PB (2.75 Ωarag) in 2100, and it allows staying within the PB in 2300 (2.97 Ωarag). REF shows a similar increase in 2100, but a slightly smaller increase in 2300 (2.86 Ωarag) compared to OAE.
To conclude, only in the far future, large-scale CDR will help stay within the PB or upper PB of most of the explored control variables; however, CDR impacts are mainly minor compared to SSP1-2.6.
How to cite: Di Natale, C. M., De Sisto, M., Prütz, R., Nordling, K., and Partanen, A.-I.: The impacts of ocean- and land-based Carbon Dioxide Removal on Planetary Boundaries, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5667, https://doi.org/10.5194/egusphere-egu26-5667, 2026.
Geological carbon storage (GCS) is a key enabler for both carbon dioxide removal (CDR) and emissions reductions from fossil fuel and industrial sources. Integrated assessment models (IAMs) provide a framework to explore the deployment of GCS in climate change mitigation scenarios and the associated resource requirements. However, the representation of GCS within IAMs is often highly simplified. This work reviews geological and technoeconomic constraints on GCS with the specific aim of improving the representation in IAMs. By exploring the levels and rates of GCS deployment in IAMs, it is possible to identify which constraints are likely to be important and, critically, which ranges of key parameters matter for model outcomes.
We review a rapidly growing body of literature and data sources on geological, technical, economic, and institutional constraints. Three factors primarily determine the availability of GCS: total theoretical geological storage capacity, physical constraints on annual injectivity due to reservoir pressure build-up, and limits on the rate of technological growth. While total theoretical geological storage capacity represents an upper bound on the resource available for carbon storage, injectivity and growth constraints determine how much of this resource can be accessed over relevant modelling timescales. The price of GCS is shaped not only by these availability constraints but also by institutional and market conditions (investability limits), proxied by historic oil and gas production and storage readiness indicators. In addition, subsurface uncertainty increases operational and characterisation costs, as well as failure rates. Together, these factors—along with social and political acceptance—control both the scale and cost at which GCS can contribute to mitigation pathways in IAMs.
Building on this review, we propose a transparent methodological workflow for constraining GCS in IAMs. The framework defines total and annual GCS capacity at global and regional scales by progressively applying geological, technical, injectivity, growth, and investability constraints, producing cost–supply curves, along with associated uncertainties, suitable for IAM implementation. These constraints are then tested within IAM scenarios to assess which ranges of total capacity, annual injection rates, and growth parameters are relevant under different mitigation pathways.
We find that total global theoretical storage capacity is unlikely to be the dominant constraint on GCS deployment this century. Despite regional constraints, even conservative global estimates are not exhausted in most climate change mitigation scenarios. Instead, annual injection capacity and the rate at which GCS infrastructure can scale are identified as the key limiting factors. Defining these constraints is essential for improving IAM representations of GCS and its role in CDR-based climate mitigation strategies.
How to cite: Harris, C., Daioglou, V., Merfort, A., De Jonge-Anderson, I., Krevor, S., and Van Vuuren, D.: Incorporating Geological Carbon Storage Constraints in Integrated Assessment Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20568, https://doi.org/10.5194/egusphere-egu26-20568, 2026.
Ocean alkalinity enhancement (OAE) is an approach for the deliberate removal of CO2 from the atmosphere. This emerging technology relies on human intervention to increase the alkalinity of seawater which, in turn, induces a net flux of atmospheric CO2 into the ocean. OAE is considered comparatively scalable and promises to deliver durable carbon removal but, to the best of our knowledge, a detailed feasibility study has not been undertaken. Key aspects to consider in such an analysis are: 1) how much alkalinity can be added at coastal outfall sites before breaching regulatory and geochemical constraints on seawater pH and carbonate saturation state, and 2) whether delivery of alkalinity can be achieved with a sufficiently low carbon footprint. We present results addressing both questions using the coast of Nova Scotia in eastern Canada as a test case. The first operational deployment of OAE started in Halifax Harbour, Nova Scotia, in October 2023. By October 2025, the climate-tech company Planetary Technologies had retired carbon credits for the removal of 1,800 tons of CO2. We ask what it would take to scale up from an annual net carbon removal of 1000 t/y of CO2 to 1 Gt/y, which is commonly considered the threshold for a carbon removal technology to be scalable. Specifically, we analyze the maximum CDR capacity of individual outfalls since this will meaningfully influence deployment strategies for OAE. Our results are based on a suite of simulations using a coupled circulation-biogeochemical model for Halifax Harbour that has been used to support OAE field work and verification of OAE credits and a prospective Life Cycle Analysis conducted for this site.
How to cite: Fennel, K., Laurent, A., Myridinas, M., Berman, H., Kracke, F., and Savitskaya, J.: Is the removal of atmospheric CO2 via Ocean Alkalinity Enhancement feasible for climate mitigation?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6163, https://doi.org/10.5194/egusphere-egu26-6163, 2026.
Carbon dioxide removal (CDR) technologies are increasingly considered a necessary complement to deep emissions reductions for meeting climate targets. However, large-scale CDR deployment involves trade-offs across multiple systems, including land, energy, water, and human health. Direct air carbon capture and storage is highly energy-intensive, while bioenergy with carbon capture and storage and biochar, are land-intensive. Enhanced rock weathering may also pose non-negligible human and environmental toxicity risks. Together, these trade-offs raise concerns about the sustainable scale of CDR deployment. This study applies the specific techno-economic logic of the global energy system model MESSAGEix to navigate these trade-offs. By incorporating spatially explicit constraints from the global land use allocation model MAgPIE, we assess how the MESSAGEix optimization framework responds to biodiversity intactness index targets and toxicity limits. The results within this specific modeling framework show that these constraints substantially alter both the composition and spatial distribution of CDR technologies. These findings highlight the importance of consistently aligning energy model topology with land-based sustainability impacts and demonstrate one potential pathway for regionally tailored CDR portfolios that align climate mitigation with broader sustainability objectives.
How to cite: Sheng, D., Pratama, Y., Brutschin, E., Sengupta, S., Dietrich, J., Riahi, K., Steinhauser, J., and Fricko, O.: Towards sustainability-aware carbon dioxide removal deployment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20118, https://doi.org/10.5194/egusphere-egu26-20118, 2026.
Most national climate pledges and climate change mitigation scenarios assessed by the IPCC
assume substantial deployment of land-based carbon dioxide removal (CDR) to meet the
temperature goals of the Paris Agreement. This reliance implies a large land footprint: land-based
CDR in national pledges and IPCC AR6 pathways can require land areas up to around one
billion hectares, comparable in magnitude to today’s global cropland area. At these scales, land
competition becomes a binding constraint, with significant trade-offs for food security,
livelihoods, and biodiversity.
Integrated assessment models (IAMs) are widely used to evaluate the role of CDR in mitigation
pathways, yet they often represent land-system constraints in a crude fashion. Previous studies
typically rely on models with simplified biophysical processes and coarse spatial resolution,
obscuring sub-regional heterogeneity in land suitability and carbon dynamics. This limitation is
particularly salient given evidence from process-based ecosystem studies that CDR potentials
vary strongly across space. Additionally, most IAM studies assess only a narrow subset of CDR
options, potentially underestimating total removal potentials and overstating land competition.
The emphasis is typically placed on land-intensive approaches like afforestation/reforestation
(A/R) and bioenergy with carbon capture and storage (BECCS), while underrepresenting
approaches that can be co-deployed on agricultural lands, such as biochar and enhanced rock
weathering (ERW). Consequently, potential synergies between CDR and other land uses, for
example through crop yield improvements, remain insufficiently explored.
We address these gaps by extending the IMAGE integrated assessment framework with a newly
developed IMAGE-CDR module that directly couples the energy system model TIMER with the
land system model IMAGE-Land/LPJmL. IMAGE-CDR estimates the spatial and temporal
deployment of land-based CDR by allocating land across competing options subject to demand,
biophysical potential, land suitability, deployment-rate limits, and economic feasibility. The
module operates on a 5′×5′ global grid and represents fractional land allocation within each grid
cell. Competition between CDR options is resolved through grid-cell-level net present value
profitability ranking, while land scarcity and interactions with agriculture are captured through a
land-cost supply curve that increases the opportunity cost of land as competition intensifies.
IMAGE-CDR represents A/R, bioenergy crops (with optional carbon capture and storage to
enable BECCS), ERW, and biochar.
Using scenario analysis, we compare the spatial deployment of land-based CDR across three
mitigation pathways: (i) current policies, (ii) a stringent target with limited overshoot, and (iii) a
less stringent target with high overshoot. We quantify method-specific removal trajectories, land
footprints, and removal efficiency per unit of land, and identify regional hotspots of feasible
deployment. We further assess interactions with food production and biodiversity conservation
by mapping overlaps with cropland and conservation priority areas and quantifying impacts on
food security and biodiversity. Our results inform the design of land-based CDR strategies by
mapping feasible deployment and associated trade-offs across regions and mitigation pathways.
How to cite: Rhalem, O., Daioglou, V., Doelman, J., Scherrenberg, M., and van Vuuren, D.: Competing for land: mapping potentials and trade-offs of land-based carbon dioxideremoval under climate targets, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22823, https://doi.org/10.5194/egusphere-egu26-22823, 2026.
Afforestation influences climate not only through carbon sequestration but also by altering surface albedo. In high-latitude regions, reductions in albedo associated with increased forest cover can induce warming that partially or fully offsets biomass-driven cooling. However, existing assessments of albedo impacts from reforestation in temperate regions largely rely on coarse-resolution, global-scale analyses, creating a significant gap between current scientific understanding and the practical evaluation of region-specific reforestation initiatives. Here, we investigate the net climate impacts of afforestation at the regional scale using three provinces in Mongolia as case studies. In contrast to earlier global-scale assessments, we apply regionally calibrated, albedo-related parameters that improve the representation of snow cover fraction and surface radiation processes. Our results indicate that afforestation in the three Mongolian provinces leads to net climate cooling, reversing conclusions drawn from previous global-scale assessments. This suggests that reliance on global-scale assessments may underestimate the climate benefits of afforestation in temperate regions, highlighting the importance of region-specific analyses for informing reforestation initiatives.
How to cite: Chang, Y.-H. and Weng, W.: Climate impacts of afforestation in temperate regions: a regional assessment in Mongolia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17876, https://doi.org/10.5194/egusphere-egu26-17876, 2026.
Carbon removal technologies (CDRs) may play a crucial role in achieving China’s carbon neutrality target, especially given the relative fast period between the emission peak and the net-zero goal (less than 35 years). However, current deployment of CDRs falls significantly behind that suggested by model-based scenarios. These scenarios typically focus on bioenergy with carbon capture and storage (BECCS), direct air capture and storage (DACCS) and reforestation, but at this stage only the latter plays a major role in near-term mitigation efforts. In this study, we use the GCAM-China model to explore a wider set of CDR options (including biochar and enhanced weathering, (EW)) to explore whether this leads to a more diverse CDR strategy. Simulations are applied at the provincial-level to increase model resolution. The results show that this indeed leads to a more diversified CDRs portfolio that may ensure the rational use of biomass resources and avoid overreliance on BECCS, a single technology not proven at large scale. In fact, EW could surpass BECCS as a more suitable option for large-scale deployment, especially in Inner Mongolia and Heilongjiang provinces. Biochar, on the other hand, is suited for small-scale application in provinces like Guangdong and Fujian. With the development of EW and biochar, residues resources can satisfy the demand for bioenergy and further reduce the resources depletion rate to 27.2%. Moreover, investing 0.5% of GDP in CDR industries can reduce transition costs by 50% (32.7 trillion USD from 2020 to 2060) compared with an investment of 0.1% of GDP.
How to cite: Wang, R., Fuhrman, J., Ou, Y., van Vuuren, D., Daioglou, V., Schmidt Tagomori, I., Pistolesi, G., Cai, W., and Wang, C.: Enhanced weathering and biochar can contribute over 50% of carbon removal while reducing costs and resource depletion in China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8183, https://doi.org/10.5194/egusphere-egu26-8183, 2026.
Carbon dioxide removal (CDR) is a core component of U.S. decarbonization strategies, yet the emerging CDR market is developing unevenly across states. While federal incentives play an important role, state-level spatial patterns and policy contexts strongly shape where projects are developed, which technologies are deployed, and which actors invest. This study aims to answer: how do state-level spatial variation and policy contexts structure the market landscape of CDR deployment in the United States?
To address this question, we construct a project-level dataset of U.S. CDR activities by compiling and harmonizing data from multiple public sources. Projects are categorized by technology type and investor class, and capacity is consistently attributed across participating investors to enable comparative analysis across states. Where capacity information is incomplete, targeted data collection and statistical imputation are used to ensure analytical coverage.
The results reveal a segmented market shaped by strong spatial and place-based dynamics. Capture projects are geographically widespread but typically small in scale, whereas storage capacity is highly concentrated in a limited number of states. Investor participation varies systematically across both technologies and states: industrial emitters and oil and gas–linked actors dominate capacity in storage-oriented states, while technology firms, corporate buyers, and public actors play a larger role in states supporting emerging capture pathways. More importantly, cross-state variation in capacity concentration and investor diversity cannot be explained by policy incentives alone, highlighting the influence of broader spatial and historical factors.
By empirically mapping technologies, investors, and geography, this study provides a market-centered perspective on the early U.S. CDR landscape. The findings highlight the importance of distinguishing between project counts and capacity, capture and storage pathways, and investor roles when assessing CDR deployment trajectories, and they underscore how market formation in CDR is shaped jointly by technological maturity, capital preferences, and place-based constraints rather than policy signals in isolation.
How to cite: Zhu, M., Vaddeboina, S., Tibebu, T., and Li, Y.: Subnational Patterns in Carbon Dioxide Removal Deployment in the United States, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14750, https://doi.org/10.5194/egusphere-egu26-14750, 2026.
Effective carbon dioxide removal (CDR) strategies are urgently needed to reduce the risks of climate change. Here, we propose a new strategy for ocean alkalinity enhancement that targets the land-to-ocean component of the inorganic carbon cycle: river alkalinity enhancement (RAE). RAE adapts freshwater acidification mitigation technology to capture CO2 through mineral weathering and by increasing rivers' capacity to retain and transport bicarbonate to long-term storage in the ocean. Global-scale modelling of RAE potential indicates that millions of tonnes of CDR per year is possible. We present data from an active project in Norway showing that RAE delivers ecological co-benefits, while meeting CDR criteria, including safety, scalability, permanence, and a simple quantification approach based directly on in-situ measurements.
How to cite: Sterling, S., Trueman, B., Bahler, I., Brenan, C., Dale, J., Duke, P., Halfyard, E., Lam, A., Tucker, J., Vogt, R., and Nelson, N.: River Alkalinity Enhancement as a Carbon Dioxide Removal Strategy: a Norwegian Case Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21935, https://doi.org/10.5194/egusphere-egu26-21935, 2026.
Surface ocean alkalinity enhancement (OAE), through the release of alkaline materials (feedstock), is an emerging abiotic marine technology for marine carbon dioxide removal that could increase the storage of anthropogenic carbon in the ocean. Alkaline feedstock may, in theory, be released at any location in the surface ocean, but the use of pre-existing coastal infrastructures (e.g., sewage outfalls, cooling pipes) is cost efficient and lowers the emissions associated with the transport of feedstock. Release at these locations is regulated and needs to occur within safe environmental thresholds. It is therefore essential to understand how point source feedstock release alters the carbonate system to 1) maximize dosing while 2) ensuring the resulting perturbations remain within the safe zone of carbonate system parameters. Influencing factors may be the dosing level, the type of feedstock, pipe design and proximity of neighboring pipes, the background state of the carbonate system, and local circulation. Given the spatial distribution of some of these factors, their importance may vary regionally. Here, we use a coupled physical-biogeochemical model that is specifically designed for coastal OAE research to investigate where and how dosing can breach environmental thresholds in the Halifax Harbour and surrounding coastal areas. Simulations with various dosing rates and release sites are carried out and their results analyzed with respect to environmental thresholds (pH>9, precipitation risk). Benthic exposure to feedstock (particulate phase) is also considered.
How to cite: Laurent, A., Fennel, K., Kracke, F., and Savitskaya, J.: Coastal alkalinity addition within safe environmental thresholds: numerical experiments in Halifax Harbour and surrounding areas (Canada), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13726, https://doi.org/10.5194/egusphere-egu26-13726, 2026.
Carbon dioxide removal (CDR) is essential for achieving net zero and net-negative emissions, yet robust monitoring, reporting, and verification (MRV) remains a major challenge. Current accounting practices are fragmented, with inconsistent system boundaries and a narrow focus on carbon, overlooking wider environmental impacts and co-benefits. Drawing on five years of research and demonstration under the UK GGR-D Programme, the most long-term global MRV effort, with multiple years of monitoring across multiple CDR technologies, this study proposes a harmonized framework for defining system boundaries across six key CDR approaches: biochar, bioenergy with carbon capture and storage (BECCS), direct air capture with storage (DACCS), peatland restoration, enhanced rock weathering, and afforestation. We map data availability for evidencing net removal across full supply chains, including the capture of CO2 from the atmosphere and its final storage, and assess gaps in environmental impact data. Our findings show that harmonization is feasible across diverse CDR methods—land-based, engineered, and hybrid land-based - engineered—but data coverage is uneven, particularly for non-carbon metrics. These gaps pose risks for sustainability assessments and the credibility of CDR claims, with implications for emerging policy frameworks and carbon markets. This work provides actionable insights for developing robust MRV systems that support transparent, sustainable CDR deployment at scale.
How to cite: Butnar, I., House, J., Thoppil, M., Martirosian, N., Mouchos, E., Lynch, J., Vetter, S., Gamaralalage, D., Tang, Y., McKechnie, J., Foteinis, S., Rodway-Dyer, S., Roeder, M., Sogbesan, S., Hastings, A., Renforth, P., Brander, M., Brown, R., Price, C., and Hodgins, G. and the UK GGR-D team: Toward Credible Carbon Dioxide Removal: Harmonized Accounting and Data Gaps Across Six CDR Approaches, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17542, https://doi.org/10.5194/egusphere-egu26-17542, 2026.
With the 1.5 °C target rapidly approaching, net-zero emissions plans routinely call for the rapid expansion of offsets based on carbon removals. This is particularly true in sectors such as aviation, where decarbonisation options are limited or progressing slowly. To comply with like-for-like offsetting requirements, such sectors will likely rely on durable CO₂ offsets, which may be delivered through bioenergy production or direct air capture combined with geological CO₂ storage. If geological CO2 removals are to ensure broad societal buy-in and market integration, they must be underpinned by robust Measurement, Reporting and Verification (MRV) and certification systems. These systems must also be recognised by a diverse set of policies, standards, and voluntary schemes.
This study investigates what certificates for geological CO₂ removal would need to look like to play a meaningful role in the decarbonisation of the aviation sector. Aviation provides a relevant focus because it is a strong use-case for high-durability offsets since direct decarbonisation options such as sustainable and low-carbon aviation fuels have high energy demands and feedstock limitations. Moreover, these options partially overlap with components of geological CO2 removals and similarly rely on extensive certification under aviation climate policy frameworks.
To address this question, we conduct a comprehensive empirical assessment that: identifies the most common MRV and certification criteria embedded in leading policies and standards; and evaluates the certification requirements for geological CO₂ removal. Based on this mapping, we identify priority design features that geological CO₂ offsets would need to satisfy to achieve policy recognition and market uptake in aviation.
To do so, we analyse a corpus of 10 policies and over 45 supporting documents, including carbon-crediting and voluntary carbon market (VCM) frameworks, as well as aviation-related policies and fuel mandates. These control the design of certification programmes and how geological CO2 removals may integrate in the aviation sector. We combine natural-language processing with an LLM-as-a-judge approach to assess the presence and strength of certification criteria across policies, followed by manual expert coding of a subset to identify differences in requirements. These 38 criteria span governance, adaptability, quantification, counterfactuals, MRV, permanence, accounting integrity, and sustainability safeguards.
We find that criteria most consistently present across both policy families relate to MRV (reporting, verification, recordkeeping), quantification (system boundaries, demonstrable climate benefits), counterfactuals (baselines and leakage), and accounting (registries and tracking) and governance (compliance). Fuel policies place stronger emphasis on quantification, boundaries, reporting, and compliance, but tend to be less specific with respect to governance, permanence, long-term accounting, and social safeguards. When manually assessing certification requirements, we find recent certification standards (Paris Agreement 6.4, ICVCM, CRCF) to perform best as they have extensive and specific requirements. Fuel policies, on the other hand, are more explicit in their treatment of lifecycle quantification for narrowly defined pathways.
How to cite: Brazzola, N., Martirosian, N., Jenkins, S., Jiang, K., House, J., Allen, M., and Kettlety, T.: Certification and MRV requirements to operationalise geological offsets in the aviation sector, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1980, https://doi.org/10.5194/egusphere-egu26-1980, 2026.
Carbon dioxide removal (CDR) is becoming increasingly relevant as a complement to rapid and sustained greenhouse gas emission reductions in overshoot pathways and pathways that limit warming to 1.5–2°C. Marine CDR (mCDR) could contribute by enhancing ocean uptake and storage of carbon, but only if Monitoring, Reporting, and Verification (MRV) can robustly quantify net removals and detect impacts. Ensuring that such interventions are effective, verifiable, and environmentally sustainable requires robust MRV systems that enable transparent carbon accounting and early detection of impacts. Yet MRV for mCDR faces a fundamental challenge because the ocean is highly variable and strongly advective, and carbon and tracers can be rapidly redistributed across space, depth, and jurisdictional boundaries.
Building on the European Marine Board Future Science Brief on MRV for mCDR, which synthesises the state-of-the-art in MRV for mCDR and provides actionable recommendations for policymakers, practitioners, and research funders, this presentation highlights key scientific and operational priorities. We present a practical six-pillar MRV framework centred on baselines, additionality, detection and attribution, durability, non-CO2 greenhouse gases, and environmental and biodiversity indicators. The framework is designed to demonstrate that observed changes exceed natural variability and can be translated into net atmospheric CO2 removal with decision-relevant uncertainty.
We argue that fit-for-purpose MRV must integrate targeted in situ observations and autonomous platforms with mechanistic, regional, and Earth system modelling, supported by model–data fusion and machine learning where direct high-frequency or long-term measurements are not feasible. MRV should expand beyond net CO2 uptake to include indicators of impacts and side effects such as carbonate chemistry, oxygen, nutrients, and ecosystem responses, with monitoring intensity scaled to project ambition and risk and linked to adaptive management levers. We conclude with recommendations on standardised MRV requirements, sustained carbonate-system observing, stronger model validation against observations, and clear limits on scaling or co-deployment until MRV protocols are demonstrated, while rapid reductions in CO2 emissions remain the top priority.
How to cite: Muri, H., Sulpis, O., Arguello, G., Baker, C., Boettcher, M., García-Ibáñez, M. I., Kuliński, K., Landolfi, A., Landschützer, P., McGovern, E., Ninčević Gladan, Ž., Oschlies, A., Yfantis, E., and Muniz Piniella, Á.: Advancing Monitoring Reporting and Verification for marine Carbon Dioxide Removal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7055, https://doi.org/10.5194/egusphere-egu26-7055, 2026.
Lime is an essential industrial material used in more than 200 applications across the European value chain, including steelmaking, water treatment, flue gas cleaning, construction, and emerging uses related to critical raw materials and marine environments. In downstream applications, lime reacts with CO₂ to form calcium carbonate through recarbonation. Recarbonation has been recognised by the IPCC since 2006 as a mechanism for CO₂ uptake and permanent storage, yet recarbonation of lime-based materials remains largely excluded from current carbon dioxide removal (CDR) assessments and accounting frameworks.
This contribution presents new academic results on carbonation of lime-based materials, complemented by emerging evidence from marine systems, with a focus on quantification, permanence, and relevance for CDR accounting. New results are reported for lime-based systems used in soil stabilisation and water treatment, alongside established construction and environmental applications. The analysis builds on the methodological framework developed by Politecnico di Milano (PoliMI) and applies mass-balance and life cycle–based approaches to quantify CO₂ uptake under real-use conditions.
High carbonation rates are observed in specific applications, notably drinking water and wastewater treatment (up to 100% within months), air-lime mortars (up to ~80–90% over their service life), and pulp and paper applications (up to ~93%, instantaneous). Soil stabilisation and other civil engineering applications exhibit lower but non-negligible CO₂ uptake over longer time horizons, depending on exposure conditions and material properties. These results confirm that recarbonation is highly application-dependent and that time-resolved modelling is essential for robust quantification.
These findings are placed in the context of broader PoliMI conclusions, which show that across major European lime applications, representing around 80% of the EU market, recarbonation reabsorbs on average approximately 33% of process CO₂ emissions, largely within the first year of use. The PoliMI work further demonstrates that recarbonation constitutes permanent carbon storage and that both spontaneous and enhanced pathways can be consistently addressed within life cycle and mass-balance frameworks.
For marine systems, the contribution discusses emerging research on ocean alkalinity enhancement using lime-based materials, indicating potential for additional atmospheric CO₂ uptake while highlighting remaining uncertainties related to environmental impacts, monitoring, and governance.
By combining new terrestrial results with established academic evidence and emerging marine research, this contribution positions lime recarbonation as a scientifically validated and permanent mineral-based CDR pathway rooted in well-understood chemistry and long-standing industrial practice.
How to cite: Di Croce, P.: Recarbonation of lime-based systems: new quantitative evidence for permanent mineral carbon dioxide removal (CDR)., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6569, https://doi.org/10.5194/egusphere-egu26-6569, 2026.
Direct air capture (DAC) is gaining prominence in carbon management and carbon dioxide removal (CDR) discussions, yet its feasibility depends strongly on deployment context and regeneration energy. Indoor environments provide a practical deployment context where elevated CO₂ can impair comfort, work efficiency, and health; however, indoor air is typically humid, and water–CO₂ co-adsorption can reshape both capture capacity and energy demand. Here we quantify these trade-offs for five representative amine-functionalized sorbents—PEI-SBA-15, TEPA-SBA-15, PEI-HP-20, een-Mg₂(dobpdc)-boc, and Lewatit—operated via thermal swing adsorption (TSA, regenerated at 90 °C) under indoor-relevant conditions. The materials span impregnated amines on porous supports (PEI/TEPA-SBA-15, PEI-HP-20), a commercial amine-functionalized ion-exchange resin (Lewatit), and an amine-appended MOF (een-Mg₂(dobpdc)-boc), enabling cross-class comparison relevant to indoor deployment.
Experiments were conducted at 25 °C under a CO₂ concentration of 2000 ppm with relative humidity (RH) spanning 20–80%. CO₂ capture capacities range from 1.05–3.24 mmol g⁻¹ at 20% RH to 1.22–3.71 mmol g⁻¹ at 50% RH and 1.68–3.62 mmol g⁻¹ at 80% RH (material-dependent). The highest capacity is achieved by TEPA-SBA-15 (3.71 mmol g⁻¹ at 50% RH), whereas other sorbents exhibit either near-saturation at intermediate RH (e.g., PEI-SBA-15) or continued capacity gains toward high RH (e.g., PEI-HP-20, Lewatit, and een-Mg₂(dobpdc)-boc). Comparative kinetics at 25 °C and 50% RH, fitted with the Avrami model, show half-times of 34.9–109.0 min with k = 0.0156–0.0278 min⁻¹ and n = 1.092–1.706. The humidity-related capacity enhancement is accompanied by a pronounced regeneration-energy penalty due to coupled water uptake. Across the five sorbents, the total specific regeneration heat (kJ mol⁻¹ CO₂; including sorbent and H₂O sensible heating and CO₂/H₂O desorption) is 186.66–522.33 at 20% RH and increases to 233.32–772.59 with increasing humidity; at 80% RH it is 1.25–2.23 times higher than at 20% RH, consistent with the sharply increasing contribution of water desorption to the total regeneration heat. Cycling tests at 25 °C, 50% RH, and 2000 ppm further reveal durability differences: PEI-SBA-15 and PEI-HP-20 show negligible capacity loss after 10 cycles, Lewatit shows ≤1.6% loss after 10 cycles, TEPA-SBA-15 shows ≤11.6% loss after 10 cycles, whereas een-Mg₂(dobpdc)-boc loses 28.2% after only 3 cycles.
Overall, the results identify humidity-driven regeneration-energy penalties and material-dependent durability as key feasibility limits for indoor DAC via TSA, providing quantitative guidance for sorbent selection and RH operation to balance capacity, kinetics, stability, and regeneration energy in indoor deployment.
How to cite: Zhuo, Y., Gong, H., Dong, Q., Li, X., and Lee, S.: Quantifying Humidity-Driven Regeneration Heat Penalties in Indoor DAC with Amine-Functionalized Sorbents, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19189, https://doi.org/10.5194/egusphere-egu26-19189, 2026.
The largest driver of future climate will be emissions of greenhouse gases and aerosols from human activity. With ongoing climate warming, the task of reducing global emissions is becoming increasingly pressing. To reach net zero emissions, strong emission reduction is needed, however there are emissions that will be hard to avoid. These need to be compensated for with new technologies. Ocean Alkalinity Enhancement (OAE) is a method for ocean-based Carbon Dioxide Removal (CDR) and describes the sequestration of CO2 from the atmosphere through the deliberate increase of ocean alkalinity. There are multiple definitions for the carbon uptake efficiency of OAE. In this study, we run experiments with the FOCI Earth system model with alkalinity additions at eight different sections of the European coast. Based on these experiments and a reference simulation without alkalinity enhancement, we use three different metrics to calculate the CO2 uptake efficiency based on a) alkalinity and ocean carbon inventories, b) carbon fluxes through the ocean surface, and c) changes to the global atmospheric CO2 concentration. We highlight challenges and benefits of each method and put it into context of efficiency evaluation for future OAE application studies.
How to cite: Teske, V., Kemena, T., and Oschlies, A.: Challenges of efficiency calculations for OAE in the Earth System Model FOCI, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17966, https://doi.org/10.5194/egusphere-egu26-17966, 2026.
One promising method of marine carbon dioxide removal is ocean alkalinity enhancement (OAE), which has the potential to sequester CO2 on timescales of up to hundreds of thousands of years (Oschlies et al. 2023). In order to quantify the potential contribution of OAE towards net zero targets, a comprehensive monitoring, reporting and verification (MRV) network is required. However, a significant challenge for MRV is the weak signal of OAE compared to natural variability of the marine carbonate system (Ho et al. 2023), including a seasonal cycle in pCO2 which is expected to amplify with ongoing climate change (Gallego et al. 2018). For this reason, in-situ observations must be complemented by modelling studies.
The seasonal cycle in the marine carbonate system has been shown to influence whether a region is a source or sink of CO2 (Fassbender et al. 2018), and has been shown to modulate detectability of alkalinity variations due to OAE (Wang et al. 2024). We use a coupled Earth system model with an ocean biogeochemistry component to explore the impact that OAE has on the seasonal cycle of the marine carbonate system and the implications this has for MRV. We simulate continuous alkalinity addition along the exposed coastlines of the North Sea/North Atlantic, and in the Chinese Exclusive Economic Zone. For each simulation, we quantify the change in the seasonal cycle in the region of alkalinity addition, the regions where the seasonal cycle is most strongly affected, and the time it takes for the signal of changing seasonality to emerge. Thus, we can consider whether the impact of OAE on seasonality in the carbonate system can be used to: enhance detectability of OAE; to define optimal timing of alkalinity addition; or to provide further guardrails for implementation based on the environmental or ecological impact of the changing seasonal cycle.
How to cite: Avrutin, S., Oschlies, A., and Ciscato, C.: Using the Seasonal Cycle in the Ocean Carbonate System for Monitoring and Guiding OAE, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18169, https://doi.org/10.5194/egusphere-egu26-18169, 2026.
Anthropogenic climate change is amplifying carbon-cycle perturbations across aquatic and terrestrial systems, increasing the need for accurate greenhouse-gas accounting. Rivers, though limited in global surface area, exert outsized influence on the carbon and alkalinity balance through coupled weathering and gas-exchange processes and are estimated to emit ~1.8 Pg C yr-1 as CO2. A key unresolved challenge is the absence of a systematic, scalable approach to quantify CO2 evasion from short, high-energy lotic segments – hydraulic “hotspots” where dissolved CO2 and exchange rates change sharply over space and time. Discrete features such as steps, cascades, and waterfalls can dominate reach-scale CO2 evasion despite occupying negligible surface area, yet prevailing monitoring approaches rarely resolve step-specific contributions, often miss local dynamics occurring over seconds to minutes, and do not yield low-cost proxies suitable for widespread deployment. This knowledge gap is especially consequential for River Alkalinity Enhancement (RAE), a carbon dioxide removal (CDR) strategy in which alkaline minerals, such as calcite, are added to raise alkalinity and dissolved inorganic carbon, lower aqueous pCO2, and promote conversion of atmospheric CO2 to bicarbonate for long-term ocean storage. If dosed waters traverse high-energy steps during equilibration, turbulence-driven gas exchange may provide a mechanism for improving removal efficiency and CDR credibility by reversing the gradient of CO2 invasion. This research presents the ongoing development of an approach to quantify step-resolved CO2 evasion by measuring pCO2 “damping” across discrete hydraulic steps, with avenues to examine other factors influencing simulated reach evasion. Controlled mesocosm experiments systematically vary hydraulic conditions while collecting high-frequency dissolved CO2 observations under baseline and calcite-dosed scenarios, enabling empirical constraints that support scalable hotspot accounting, improved RAE siting and design.
How to cite: Bahler, I. and Sterling, S.: Quantifying pCO₂ Evasion at River Steps: Hydraulic Controls Under Baseline and Alkalinity-Dosed Conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21964, https://doi.org/10.5194/egusphere-egu26-21964, 2026.
Land use transformations significantly influences the balance between soil organic carbon (SOC) sequestration and greenhouse gas emissions. Amidst the escalating global climate crisis, unraveling the impacts of ecological restoration and conservation practices on greenhouse gas dynamics across diverse land uses becomes increasingly urgent, especially within ecologically sensitive karst landscapes. This study conducted monthly monitoring of CO₂ and CH4 fluxes coupled with stable isotope analysis (δ¹³CCO₂) from March 2023 to February 2024, encompassing four different land use types (farmland, grassland, shrubland, and forest) in a subtropical karst region of southwest China. For comparison, a non-karst forest land located less than 1 km away was also monitored. Principal findings include: (1) Compared to non-karst areas, karst soils exhibited significantly lower CO₂ emission rates (p < 0.01), showing a sequential deline along vegetation succession gradients: shrubland (134.93±70.5 mg C m⁻² h⁻¹) > forest (131.56±66.75 mg C m⁻² h⁻¹) > farmland (129.91± 81.72mg C m⁻² h⁻¹) > grassland (124.31±54.82 mg C m⁻² h⁻¹). The positive δ¹³CCO₂ values (1.8‰ to 3.5‰) indicate preferential depletion of the lighter carbon isotope (¹²CO₂) through karst dissolution processes, resulting in relative enrichment of the heavier isotope (¹³CO₂) within the system. (2) Progressive vegetation succession significantly enhanced karst carbon sequestration, with subsurface dissolution rates peaking at 14.31 mg cm-²·yr-1 during the shrubland stage. The dissolution rates increased by 4.76-15.94 mg cm-²·yr-1 along the grassland-to-shrubland succession sequence, demonstrating the predominant role of pioneer shrub communities in promoting carbon sink potential. (3) Structural equation modeling (SEM) pathway analysis revealed distinct regulatory mechanisms: soil CO₂ fluxes were primarily driven by microbial biomass carbon (MBC) and temperature (R²=0.79), while δ13CCO₂ fractionation was co-regulated by pH, moisture, MBC, and dissolution rates (R²=0.78). These findings demonstrate that karst processes enhance subsurface carbon sequestration through dual mechanisms: reducing net soil CO₂ emissions and promoting inorganic carbon transfer to groundwater systems via intensified carbon isotope fractionation effects. This study provides the quantitative elucidation of the coupled relationships among vegetation succession, karst processes, and carbon isotope fractionation. It offers critical scientific evidence for optimizing ecological restoration strategies and advancing carbon neutrality objectives in subtropical karst ecosystems.
How to cite: zhu, D.: Karst carbon sink: Evidence from long term monitoring of CO2 and CH4 fluxes with stable isotope insights in subtropical Southwest China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12728, https://doi.org/10.5194/egusphere-egu26-12728, 2026.
Enhanced Rock Weathering (ERW) has attracted increasing attention as a carbon dioxide removal (CDR) approach, yet its implementation depends on monitoring, reporting, and verification (MRV) strategies that can reliably detect and attribute CO2 removal under different field conditions. Flooded rice paddies are considered a potentially favorable environment for ERW due to continuous water fluxes, but strong hydrological and biogeochemical dynamics also complicate signal detection. Thus, two-year field experiments were conducted at four rice paddy sites in Japan with contrasting silicon (Si) supply capacities. Finely ground basalt was applied prior to cultivation at rates of 0, 100 (5 wt%), or 200 (10 wt%) t ha-1. ERW of reactive minerals was quantified by directly tracking temporal changes in Ca-plagioclase using quantitative X-ray powder diffraction (XRPD). These mineral-based estimates were compared with cation-based estimates derived from X-ray fluorescence (XRF) measurements of total Ca loss. XRPD analyses revealed that plots amended with 10 wt% basalt exhibited significant reductions in Ca-plagioclase within one year after application across all sites, whereas such reductions were not consistently observed in the 5 wt% plots. These results provided direct field evidence of in situ mineral weathering under flooded conditions. Estimated CDR potentials for all basalt-amended plots derived from XRPD ranged from 1.1 to 9.3 t CO2 ha-1 yr-1 and were broadly consistent with, but systematically higher than, XRF-based estimates. This discrepancy likely reflects the influence of external Ca inputs that can mask Ca depletion in XRF-based approach, as well as the uncertainties associated with estimated Ca-bearing minerals from idealized mineral stoichiometries in XRPD-based calculations. Notably, both methods consistently indicated higher weathering rates and CDR potentials at sites with lower initial Si availability. In parallel, basalt application increased plant-available Si and rice straw Si uptake over two growing seasons and was associated with reduced proportions of immature grains. However, the persistence of minerals after one year underscores the need for multi-year assessments. Overall, this study demonstrates that mineralogical monitoring provides a robust MRV pathway for ERW in dynamic paddy systems and that site selection is critical for reliable detection and attribution of CDR signals under field conditions.
How to cite: Yang, C.-Y., Tomita, H., Kurokawa, K., Shinano, T., Maruyama, H., Uchibayashi, H., Yanai, J., and Nakao, A.: Enhanced Rock Weathering–Induced Carbon Dioxide Removal in Flooded Rice Paddies: Mineral-Based Monitoring from Field Experiments in Japan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16903, https://doi.org/10.5194/egusphere-egu26-16903, 2026.
Posters on site: Mon, 4 May, 16:15–18:00 | Hall X5
This study is positioned as a foundational, soil-based carbon capture and carbon dioxide removal (CDR) investigation, aiming to establish fundamental design principles for mineral- and soil-derived CO₂ sorbents rather than immediate industrial deployment. Soil and soil-like materials play a central role in long-term carbon sequestration strategies due to their abundance, stability, and compatibility with land-based CDR systems. In this context, red mud (RM), an industrial by-product of alumina production via the Bayer process, was selected as a representative mineral-rich, soil-analog material to explore its potential as a functional platform for CO₂ capture.
Globally, RM is generated at a scale of approximately 300 million tons per year, yet its reuse rate remains below 3%. Its disposal poses serious environmental concerns because of its high alkalinity, salinity, and fine particle size—characteristics that also resemble extreme or degraded soil conditions. From a soil-based CDR perspective, these properties make RM a valuable model system for investigating how mineral composition, pore structure, and surface chemistry influence CO₂ sorption behavior. Thus, this work focuses on transforming RM from an environmentally problematic residue into a functionalized, soil-like carbon capture medium.
To enable its application in soil-based carbon capture research, RM was structurally modified through acid digestion, alkali reprecipitation, and calcination. This treatment generated a mesoporous framework and increased the BET surface area from 17.47 to 140.05 m²/g, mimicking the hierarchical pore structures found in reactive mineral soils. The modified RM (ARM) therefore serves as a controlled mineral matrix for systematically studying the interaction between nitrogen-containing functional groups and CO₂.
Amine- and guanidine-functionalized sorbents were prepared by wet impregnation using polyethylenimine (PEI), triethylenetetramine (TETA), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). Rather than focusing solely on maximizing adsorption capacity, this study emphasizes understanding how different nitrogen functionalities behave when immobilized on soil-like mineral surfaces. FT-IR spectroscopy, thermogravimetric analysis, and elemental analysis confirmed the successful anchoring of these functional groups, providing a reliable platform for mechanistic investigation.
CO₂ adsorption experiments were conducted in a fixed-bed reactor under mild conditions representative of ambient or near-surface environments relevant to soil-based CDR. Among the tested materials, ARM–TETA exhibited the highest CO₂ adsorption capacity (36.90 mg/g), highlighting the importance of molecular flexibility and amine accessibility within mesoporous mineral matrices.
Overall, this research serves as a baseline study for soil-based carbon capture, demonstrating how industrial mineral residues can be engineered into model systems for CDR research. The findings provide fundamental insights into pore–functionality relationships and support the broader development of scalable, land-compatible carbon capture materials derived from soil and mineral resources.
How to cite: Cho, D.-W., Kim, H.-Y., han, H., and Yim, G.: A Fundamental Study on Soil-Based Carbon Dioxide Removal Using Amine-Functionalized Modified Red Mud, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2948, https://doi.org/10.5194/egusphere-egu26-2948, 2026.
Ocean alkalinity enhancement (OAE) is a recent focus in marine carbon dioxide removal (mCDR). The North Sea, a well-studied shelf sea, provides an ideal setting to investigate both the potential benefits and risks of OAE. During the summers of 2024 and 2025, we collected water samples from costal and offshore regions of the North Sea to measure two key parameters of the carbonate system: total alkalinity (TA) and dissolved inorganic carbon (DIC). We also quantified dissolved trace metal concentrations of nickel, vanadium, manganese, cobalt, cadmium and rare earth elements, as OAE interventions can introduce these in significant amounts.
This study aims to establish a baseline for these parameters in the North Sea and to investigate the diverse sources and sinks of TA, DIC, and trace metals. We also explore tracer-based approaches to enable monitoring of chemical impacts on the coastal environment associated with artificial OAE.
Preliminary depth profile data for TA and DIC indicate similar behavior in the southern North Sea in both years, with concentrations remaining relatively constant throughout the water column. At depth, the variation for TA is around 10 µmol/kg difference between the surface and the bottom. This difference is only slightly higher for the DIC measurements, averaging 20 µmol/kg. In the southern North Sea, the average water depth is about 40 m, and the variability between measuring stations is lower for TA than for DIC. For TA, the range of the measured values is between 2200 µmol/kg and 2400 µmol/kg, while for DIC, values between 1800 µmol/kg and 2300 µmol/kg were measured. In contrast, profiles from the Norwegian Trench with sampling depths up to 513 m show that DIC concentrations are lowest at the surface, averaging 2000 µmol/kg, and increase to an average of 2200 µmol/kg at a depth of 100 m, then remain stable to the seafloor, reflecting the production of organic matter at the surface and subsequent remineralization at depth. Data from both years suggest that TA is less variable than DIC, as it is less influenced by biological processes. This stability highlights TA’s potential as a robust monitoring parameter in the context of OAE. Furthermore, depth-profile data from summer 2025 indicate that most of the trace metals analyzed exhibit higher concentrations near the surface. Rare earth elements have low conentreations, dysprosium for example has a concentration of 1.55 ng/L at the surface and decrease to 0.98 ng/L at the seafloor. Nickel, gadolinium, and dysprosium in particular have higher concentrations in coastal area of the North Sea with low salinity, which is due to river inputs and anthropogenic influences. Near the Baltic Sea, concentrations reach a maximum of 650 ng/l for nickel, 4.2 ng/l for gadolinium, and 2.8 ng/l for dysprosium. These observations underscore the importance of understanding spatial variability in both carbonate system parameters and trace metals when evaluating OAE impacts.
The poster will present spatial patterns of TA, DIC, and trace metal concentrations across the North Sea, discuss potential tracer approaches for OAE monitoring, and highlight implications for future mCDR strategies.
How to cite: Petzold, B. A., Thomas, H., Pröfrock, D., and Zimmermann, T.: Baseline Assessment of Carbonate System Parameters and Trace Metals in the North Sea: Implications for Monitoring Ocean Alkalinity Enhancement, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6763, https://doi.org/10.5194/egusphere-egu26-6763, 2026.
With growing discourse surrounding climate repair and geoengineering in general, scientists must ask critical questions regarding the morality of such research whilst also recognising its potential importance. From a social perspective, there is a careful balance to be struck between the need for Carbon Dioxide Removal (CDR) to limit global temperature rise and ensuring that this research does not detract from efforts to reduce greenhouse gas emissions. This poster will examine these ethical considerations whilst highlighting the physical constraints of cutting-edge CDR through a process-modelling analysis.
Specific focus will be placed on the fundamental physics underpinning emerging Direct Air Capture (DAC) processes, and hence on evaluating the scalability of such technologies from a scientific perspective. In particular, a physics based transport–reaction model of Supercapacitive Swing Adsorption (SSA), which currently operates at the millimetre scale, will be presented. Analysis of this model provides insight into whether SSA can be realistically scaled to industrial levels, identifying the physical and operational factors that may limit such upscaling and thus the implications for feasible CDR deployment. This work builds upon recent research published by the Forse group within the Department of Chemistry at the University of Cambridge.
How to cite: Karia, R.: Understanding the ethics and scalibility of emerging Direct Air Capture approaches, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13642, https://doi.org/10.5194/egusphere-egu26-13642, 2026.
The climatic effect of fossil-fuel derived CO2 emissions is not necessarily equivalent to that of CO2 removals. Asymmetry often exists with respect to the long-term radiative forcing effect of the net balance between emissions (that persist in the coupled atmosphere-land-ocean system for millennia) and removals (that may only persist on decadal to centennial timescales, particularly in nature-based solutions on land). To align emissions and removals for credible net-zero claims, we introduce the concept of carbon dioxide removal equivalents (CDRe), a metric that quantifies the radiative effect of CO2 removals in proportion to the warming potential of CO2 emissions. This metric can be combined with traditional CO2 equivalents (CO2e) for emissions to obtain the net climate effect of greenhouse gas emissions and CO2 removals in a unified net-zero accounting framework.
How to cite: Sierra, C. and Crow, S.: Equivalence between carbon dioxide emissions and removals: A framework for net-zero accounting, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17442, https://doi.org/10.5194/egusphere-egu26-17442, 2026.
To meet the goals of the Paris Agreement and achieve sustainable net-zero emissions by 2050, the IPCC and the IEA highlight the critical role of carbon capture and storage (CCS) and carbon dioxide removal (CDR) methods. Current projections suggest the need to capture 1 gigaton of CO2 per year by 2030, increasing to 5 gigatons by 2045. Despite the predominance of amine-based capture in industrial applications, Integrated Assessment Models (IAMs), used to generate future pathways for global energy, land-use, and economic transformation, often rely heavily on bioenergy with carbon capture and storage (BECCS) as the main net-negative (NET) emissions technology. However, the value assigned to these technologies within IAMs often depends on the model structure and underlying assumptions that require further exploration.
This study aims to model a range of carbon dioxide removal (CDR) and carbon capture and storage (CCS) methods within the IAM FRIDA as global-scale climate mitigation strategies. The analysis assesses the mitigation potential of CDR technologies under different climate scenarios and examines the role of bioenergy with carbon capture and storage (BECCS) as a negative emissions technology. The impact of climate change on BECCS development is also evaluated. The study concludes that while CDR is essential for achieving net-zero emissions, its effectiveness is sensitive to technological development and economic offsets. This research provides an understanding of how different removal pathways contribute to avoiding dangerous climate change, while also identifying the socioeconomic limitations of these mitigation strategies.
This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025. This work has also received funding from the European Union’s Horizon 2.5 – Climate Energy and Mobility programme under grant agreement No. 101081661 through the 'WorldTrans – TRANSPARENT ASSESSMENTS FOR REAL PEOPLE' project.
How to cite: Molina, M. O., Mahú, F., Schoenberg, W., Blanz, B., and Koberle, A.: Evaluating the Potential and Risks of Carbon Dioxide Removal (CDR) and Storage (CCS) Strategies in Global Climate Mitigation: An Integrated Assessment Modeling Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18297, https://doi.org/10.5194/egusphere-egu26-18297, 2026.
Ocean Alkalinity Enhancement (OAE) is a promising method for marine carbon dioxide removal. By artificially increasing ocean alkalinity, OAE triggers chemical reactions within the carbonate system that reduce oceanic pCO₂ levels, thereby inducing an uptake of atmospheric CO₂ by the ocean. However, as alkalinity concentrations at the point of release can reach high levels, alkalinity addition is limited for environmental safety to ensure pH < 9. Pronounced alkalinity variability was observed in the Halifax Harbour (Canada), an operational OAE site since 2023. This variability is characterized by alternating high and low values with substantial differences in magnitude. Understanding the processes that generate this variability is essential for controlling its intensity and advancing toward optimized dynamic dosing strategies to maximize dosing while remaining within safe regulatory limits.
Observations of carbonate system parameters collected during and outside dosing periods in the Halifax Harbour provide a unique dataset to determine which factors control the occurrence and magnitude of the alkalinity variability. We combine in situ measurements with numerical modeling using the Regional Ocean Modeling System (ROMS), customized for the Halifax Harbour and implemented with a nested grid configuration (50–900 m horizontal resolution). We use a series of numerical simulations under different wind scenarios to examine the coupled effects of winds and tides on alkalinity dispersion.
Our results show that the concentrations of added alkalinity are primarily controlled by tidal variability on daily and monthly timescales. Wind effects act as a secondary control, modulating tidal patterns and causing notable deviations, particularly during neap tides. Winds directed toward the open ocean enhance dispersion, whereas winds blowing into the basin tend to retain alkalinity near the release site, leading to higher local concentrations.
How to cite: Berman, H., Laurent, A., Morgan, S., Atamanchuk, D., Yee, R., Musgrave, R., and Fennel, K.: Physical controls on alkalinity variability in Halifax Harbour: The roles of wind and tides, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15404, https://doi.org/10.5194/egusphere-egu26-15404, 2026.
Temporary carbon dioxide removal (CDR) dominates current deployment, while permanent solutions face feasibility and cost challenges at scale. However, efforts to integrate temporary CDR into climate policies have relied on flawed equivalency assumptions between temporary and permanent CDR that contradict physical climate science: temporary CDR cannot fully offset CO2 emissions as permanent CDR can. Instead, we demonstrate that temporary CDR can serve as compensation for non-CO2 climate forcers, particularly for short-lived species whose compensation ratios are shown to be fairly insensitive to the choice of time horizon. For instance, offsetting 1 kg CH4 requires 498 kg CO2 with 20-year temporary storage (such as bioplastics) or 101 kg CO2 with 100-year storage (such as durable wood products). We suggest a critical lifetime threshold that separates short-lived and long-lived species for temporary CDR applications, with implementation requiring differentiated reporting of these categories in climate policies. This framework enables proper crediting of temporary CDR activities in sectors like agriculture, where non-CO2 emissions dominate and direct emission reductions remain extremely challenging.
How to cite: He, Y., Riahi, K., Gidden, M., Piao, S., Wang, T., and Gasser, T.: Temporary carbon dioxide removal to offset short-lived climate forcers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10111, https://doi.org/10.5194/egusphere-egu26-10111, 2026.
