Climate change mitigation: potential benefits and pitfalls of enhanced rock weathering in tropical agriculture

The potential for carbon dioxide removal by enhanced rock weathering in the tropics: An evaluation of Costa Rica

Tropical environments show great potential to sequester CO2 by enhanced rock weathering (ERW) of powdered mafic rocks applied to agricultural fields. This study seeks to assess carbon dioxide reduction (CDR) potential in the humid tropics (1) by experimental weathering of mafic rock powders in conditions simulating humid tropical soils, and (2) from weathering rates determined from a Holocene tropical soil chronosequence where parent material is andesitic sediments. Experimentally determined weathering rates by leaching of basaltic andesites from Costa Rica (Arenal and Barva) for 50 t ha-1 applications indicate potential sequestration of 2.4 to 4.5 t CO2 ha-1 yr-1, whereas the USGS basalt standard BHVO-1 yields a rate of 11.9 t ha-1 yr-1 (influenced by more mafic composition and finer particle size). The chronosequence indicates a rate of 1.7 t CO2 ha-1 yr-1. The weathering experiment consisted of 0.6 mm of powdered rock applied atop 12 mm of Ultisol at 35 °C. To simulate a tropical soil solution, 100-mL aliquots of a dilute solution of oxalic acid in carbonated DI water were rained onto soils over a 14-day period to simulate soil moisture in the humid tropics. Solutions were collected and analyzed by ICPMS for concentrations of leached cations. A potential ERW scenario for Costa Rica was assessed assuming that one-half of lowland agricultural kaolinitic soils (mainly Ultisols, common crop and pasture soils, excluding protected areas) were to receive 50 t ha-1 of annual or biennial applications of powdered mafic rock. With an experimentally determined humid tropical CDR rate for basaltic andesite (3.5 t ha-1 yr-1) and allowances for carbon costs (e.g. emissions from processing and delivery) that reduce CDR to a net 3.2 t ha-1 yr-1, potential annual CDR of this tropical nation is ∼2-4 million tons, amounting to ∼25-50 % of annual CO2 emissions (mainly from transportation in Costa Rica).

'Climate Healing Stones': Common Minerals Offer Substantial Climate Change Mitigation Potential

This review proposes that mineral-based greenhouse gas (GHG) mitigation could be developed into a substantial climate change abatement tool. This proposal was evaluated via three objectives: (1) synthesise literature studies documenting the effectiveness of geological minerals at mitigating GHG emissions; (2) quantify, via meta-analysis, GHG magnitudes that could be abated by minerals factoring-in the carbon footprint of the approach; and (3) estimate the global availability of relevant minerals. Several minerals have been effectively harnessed across multiple sectors-including agriculture, waste management and coal mining-to mitigate carbon dioxide/CO2 (e.g., olivine), methane/CH4 (e.g., allophane, gypsum) and nitrous oxide/N2O (e.g., vermiculite) emissions. High surface area minerals offer substantial promise to protect soil carbon, albeit their potential impact here is difficult to quantify. Although mineral-based N2O reduction strategies can achieve gross emission reduction, their application generates a net carbon emission due to prohibitively large mineral quantities needed. By contrast, mineral-based technologies could abate ~9% and 11% of global CO2 and CH4 anthropogenic emissions, respectively. These estimates conservatively only consider options which offer additional benefits to climate change mitigation (e.g., nutrient supply to agricultural landscapes, and safety controls in landfill operations). This multi-benefit aspect is important due to the reluctance to invest in stand-alone GHG mitigation technologies. Minerals that exhibit high GHG mitigation potential are globally abundant. However, their application towards a dedicated global GHG mitigation initiative would entail significant escalation of their current production rates. A detailed cost-benefit analysis and environmental and social footprint assessment is needed to ascertain the strategy's scale-up potential.

A state of the art of review on factors affecting the enhanced weathering in agricultural soil: strategies for carbon sequestration and climate mitigation

As the urgency to address climate change intensifies, the exploration of sustainable negative emission technologies becomes imperative. Enhanced weathering (EW) represents an approach by leveraging the natural process of rock weathering to sequester atmospheric carbon dioxide (CO2) in agricultural lands. This review synthesizes current research on EW, focusing on its mechanisms, influencing factors, and pathways for successful integration into agricultural practices. It evaluates key factors such as material suitability, particle size, application rates, soil properties, and climate, which are crucial for optimizing EW's efficacy. The study highlights the multifaceted benefits of EW, including soil fertility improvement, pH regulation, and enhanced water retention, which collectively contribute to increased agricultural productivity and climate change mitigation. Furthermore, the review introduces Monitoring, Reporting, and Verification (MRV) and Carbon Dioxide Removal (CDR) verification frameworks as essential components for assessing and enhancing EW's effectiveness and credibility. By examining the current state of research and proposing avenues for future investigation, this review aims to deepen the understanding of EW's role in sustainable agriculture and climate change mitigation strategies.

A horizon scan of global biological conservation issues for 2024

We present the results of our 15th horizon scan of novel issues that could influence biological conservation in the future. From an initial list of 96 issues, our international panel of scientists and practitioners identified 15 that we consider important for societies worldwide to track and potentially respond to. Issues are novel within conservation or represent a substantial positive or negative step-change with global or regional extents. For example, new sources of hydrogen fuel and changes in deep-sea currents may have profound impacts on marine and terrestrial ecosystems. Technological advances that may be positive include benchtop DNA printers and the industrialisation of approaches that can create high-protein food from air, potentially reducing the pressure on land for food production.

Initial Validation of a Soil-Based Mass-Balance Approach for Empirical Monitoring of Enhanced Rock Weathering Rates

Enhanced rock weathering (ERW) is a promising scalable and cost-effective carbon dioxide removal (CDR) strategy with significant environmental and agronomic co-benefits. A major barrier to large-scale implementation of ERW is a robust monitoring, reporting, and verification (MRV) framework. To successfully quantify the amount of carbon dioxide removed by ERW, MRV must be accurate, precise, and cost-effective. Here, we outline a mass-balance-based method in which analysis of the chemical composition of soil samples is used to track in situ silicate rock weathering. We show that signal-to-noise issues of in situ soil analysis can be mitigated by using isotope-dilution mass spectrometry to reduce analytical error. We implement a proof-of-concept experiment demonstrating the method in controlled mesocosms. In our experiment, a basalt rock feedstock is added to soil columns containing the cereal crop Sorghum bicolor at a rate equivalent to 50 t ha-1. Using our approach, we calculate rock weathering corresponding to an average initial CDR value of 1.44 ± 0.27 tCO2eq ha-1 from our experiments after 235 days, within error of an independent estimate calculated using conventional elemental budgeting of reaction products. Our method provides a robust time-integrated estimate of initial CDR, to feed into models that track and validate large-scale carbon removal through ERW.

Techno-Economic and Life Cycle Assessment of Enhanced Rock Weathering: A Case Study from the Midwestern United States

Enhanced rock weathering (ERW) is a carbon dioxide removal (CDR) strategy for combating climate change. The CDR potentials of ERW have been assessed at the process and national/global levels, but the environmental and economic implications of ERW have not been fully quantified for U.S. applications with real-world supply chain considerations. This study develops an optimization-based, integrated life cycle assessment and techno-economic analysis framework for ERW, which is demonstrated by a case study applying mining waste to croplands in the Midwestern U.S. The case study explores maximum transportation distances for intermodal transportation at varied mineral CDR yields and costs, informing supply chain design for economically viable ERW. ERW costs (US$45 to 472/tonne of net CO2e captured) and cradle-to-farm gate GHG emissions (41 to 359 kg CO2e/tonne of CO2e captured) are estimated based on a range of CDR yields and by transportation distances to and from two Midwest port destinations: Chicago and Duluth. Our sensitivity analysis identifies CDR yields, and transportation modes and distances as driving factors for result variations. Our study reveals the importance of ERW supply chain design and provides an example of U.S. CDR implementation. Our framework and findings can be applied to other regional ERW projects.

Do Southeast Asia's paleo-Antarctic trees cool the planet?

Many tree genera in the Malesian uplands have Southern Hemisphere origins, often supported by austral fossil records. Weathering the vast bedrock exposures in the everwet Malesian tropics may have consumed sufficient atmospheric CO₂ to contribute significantly to global cooling over the past 15 Myr. However, there has been no discussion of how the distinctive regional tree assemblages may have enhanced weathering and contributed to this process. We postulate that Gondwanan-sourced tree lineages that can dominate higher-elevation forests played an overlooked role in the Neogene CO₂ drawdown that led to the Ice Ages and the current, now-precarious climate state. Moreover, several historically abundant conifers in Araucariaceae and Podocarpaceae are likely to have made an outsized contribution through soil acidification that increases weathering. If the widespread destruction of Malesian lowland forests continues to spread into the uplands, the losses will threaten unique austral plant assemblages and, if our hypothesis is correct, a carbon sequestration engine that could contribute to cooler planetary conditions far into the future. Immediate effects include the spread of heat islands, significant losses of biomass carbon and forest-dependent biodiversity, erosion of watershed values, and the destruction of tens of millions of years of evolutionary history.

The environmental controls on efficiency of enhanced rock weathering in soils

Enhanced rock weathering (ERW) in soils is a promising carbon removal technology, but the realistically achievable efficiency, controlled primarily by in situ weathering rates of the applied rocks, is highly uncertain. Here we explored the impacts of coupled biogeochemical and transport processes and a set of primary environmental and operational controls, using forsterite as a proxy mineral in soils and a multiphase multi-component reactive transport model considering microbe-mediated reactions. For a onetime forsterite application of ~ 16 kg/m2, complete weathering within five years can be achieved, giving an equivalent carbon removal rate of ~ 2.3 kgCO2/m2/yr. However, the rate is highly variable based on site-specific conditions. We showed that the in situ weathering rate can be enhanced by conditions and operations that maintain high CO2 availability via effective transport of atmospheric CO2 (e.g. in well-drained soils) and/or sufficient biogenic CO2 supply (e.g. stimulated plant-microbe processes). Our results further highlight that the effect of increasing surface area on weathering rate can be significant-so that the energy penalty of reducing the grain size may be justified-only when CO2 supply is nonlimiting. Therefore, for ERW practices to be effective, siting and engineering design (e.g. optimal grain size) need to be co-optimized.

Assessing long-term rainfall trends and changes in a tropical watershed Brantas, Indonesia: an approach for quantifying the agreement among satellite-based rainfall data, ground rainfall data, and small-scale farmers questionnaires

The agreement between meteorological data and societal perception is essential in supporting a robust policy making and its implementation. In humid tropic watersheds like Brantas, such consensus is important for water resources management and policies. This study exemplifies an effort to understand the long-term rainfall characteristics within the watershed and to build a common link among the differing data sources: CHIRPS rainfall satellite data, rain gauge data, and farmers perceptions. Six rainfall characteristics were derived using statistical measures from the scientific data and then were translated to a series of structured questionnaires given to small-scale farmers. A consensus matrix was built to examine the level of agreement among three data sources, supporting the spatial pattern of the meteorological data and farmers perception. Two rainfall attributes were classified with high agreement, four with moderate and one with low agreement. The agreements and discrepancies of rainfall characteristics were found in the study area. The discrepancies originated from the accuracy in translating scientific measurements to practical meanings for farmers, complexity of the farming system, the nature of phenomena in questions, and farmers' ability to record long-term climatic events. This study shows an implication that a combined approach to link scientific data and societal data is needed to support powerful climate policy making.

Geochemical carbon dioxide removal potential of Spain

Many countries have made pledges to reduce CO₂ emissions over the upcoming decades to meet the Paris Agreement targets of limiting warming to no >1.5 °C, aiming for net zero by mid-century. To achieve national reduction targets, there is a further need for CO₂ removal (CDR) approaches on a scale of millions of tonnes, necessitating a better understanding of feasible methods. One approach that is gaining attention is geochemical CDR, encompassing (1) in-situ injection of CO₂-rich gases into Ca and Mg-rich rocks for geological storage by mineral carbonation, (2) ex-situ ocean alkalinity enhancement, enhanced weathering and mineral carbonation of alkaline-rich materials, and (3) electrochemical separation processes. In this context, Spain may host a notionally high geochemical CDR capacity thanks to its varied geological setting, including extensive mafic-ultramafic and carbonate rocks. However, pilot schemes and large-scale strategies for CDR implementation are presently absent in-country, partly due to gaps in current knowledge and lack of attention paid by regulatory bodies. Here, we identify possible materials, localities and avenues for future geochemical CDR research and implementation strategies within Spain. This study highlights the kilotonne to million tonne scale CDR options for Spain over the rest of the century, with attention paid to chemically and mineralogically appropriate materials, suitable implementation sites and potential strategies that could be followed. Mafic, ultramafic and carbonate rocks, mine tailings, fly ashes, slag by-products, desalination brines and ceramic wastes hosted and produced in Spain are of key interest, with industrial, agricultural and coastal areas providing opportunities to launch pilot schemes. Though there are obstacles to reaching the maximum CDR potential, this study helps to identify focused targets that will facilitate overcoming such barriers. The CDR potential of Spain warrants dedicated investigations to achieve the highest possible CDR to make valuable contributions to national reduction targets.

Deliberating enhanced weathering: Public frames, iconic ecosystems and the governance of carbon removal at scale

Meeting goals for 'net zero' emissions may require the removal of previously emitted carbon dioxide from the atmosphere. One proposal, enhanced rock weathering, aims to speed up the weathering processes of rocks by crushing them finely and spreading them on agricultural land. Public perceptions of enhanced rock weathering and its wider social and environmental implications will be a critical factor determining its potential; we use six 2-day deliberative workshops in England, Wales and Illinois to understand public views. Consideration of enhanced rock weathering deployment in tropical countries led participants to frame it from a social justice perspective, which had been much less prevalent when considering Western agricultural contexts, and generated assumptions of increased scale, which heightened concerns about detrimental social and environmental impacts. Risk perceptions relating to 'messing with nature' became amplified when participants considered enhanced rock weathering in relation to 'iconic' environments such as the oceans and rainforest.

Changes in assembly processes of soil microbial communities in forest-to-cropland conversion in Changbai Mountains, northeastern China

In response to human-induced changes in the environment, it is crucial to assess the underlying factors of the impacts of forest conversion on ecosystem function. However, research is limited on bacteria and fungi diversity, functional properties, and community assembly mechanisms in response to forest-to-cropland conversion. We categorized soil bacterial and fungal communities from primary forest, secondary forest, and cropland in Changbai Mountains, China. We found that forest-to-cropland conversion altered the structure and composition of bacterial and fungal communities and might be associated with potential changes in function. The null models indicated that the conversion from forest to cropland enhanced the bacterial dispersal limitation process and weakened the fungal dispersal limitation processes. Furthermore, ecological drift dominates the ecological processes of cropland fungi. Both edaphic properties (the content of C: N ratio, available phosphorus, nitrate) significantly impacted on soil bacterial and fungal community structures. In addition, there were significant functional variations in the fungal community between forest-to-cropland. The ectomycorrhizal and saprotrophic fungi showed increased abundance in the forest microbial communities, whereas the endophytic and pathogenic fungal abundance was increased in cropland soil. Taken together, our data illustrate the differences in the response of bacteria and fungi to forest-to-cropland conversion in temperate forest areas and deepen our understanding of the effects of forest conversion on microbial functions and community assembly processes.

Kinetics-informed global assessment of mine tailings for CO2 removal

Chemically reactive mine tailings are a potential resource for drawing down carbon dioxide out of the atmosphere in mineral weathering schemes. Such carbon dioxide removal (CDR) systems, applied on a large scale, could help to meet internationally agreed targets for minimising climate change, but crucially we need to identify what materials could react fast enough to provide CDR at relevant climate change mitigation timescales. This study focuses on a range of silicate-dominated tailings, calculating their CDR potential from their chemical composition (specific capacity), estimated global production rates, and the speed of weathering under different reaction conditions. Tailings containing high abundances of olivine, serpentine and diopside show the highest CDR potential due to their favourable kinetics. We conclude that the most suitable tailings for CDR purposes are those associated with olivine dunites, diamond kimberlites, asbestos and talc serpentinites, Ni sulphides, and PGM layered mafic intrusions. We estimate the average annual global CDR potential of tailings weathered over the 70-year period 2030-2100 to be ~93 (unimproved conditions) to 465 (improved conditions) Mt/year. Results indicate that at least 30 countries possess tailings materials that, under improved conditions, may offer a route for CDR which is not currently utilised within the mining industry. By 2100, the total cumulative CDR could reach some 33 GtCO₂, of which more than 60% is contributed by PGM tailings produced in Southern Africa, Russia, and North America. The global CDR potential could be increased by utilization of historic tailings and implementing measures to further enhance chemical reaction rates. If practical considerations can be addressed and enhanced weathering rates can be achieved, then CDR from suitable tailings could contribute significantly to national offset goals and global targets. More research is needed to establish the potential and practicality of this technology, including measurements of the mineral weathering kinetics under various conditions.

Deriving Nickel (Ni(II)) and Chromium (Cr(III)) Based Environmentally Safe Olivine Guidelines for Coastal Enhanced Silicate Weathering

Enhanced silicate weathering (ESW) by spreading finely ground silicate rock along the coastal zone to remove atmospheric carbon dioxide (CO₂) is a proposed climate change mitigation technique. The abundant and fast-dissolving mineral olivine has received the most attention for this application. However, olivine contains nickel (Ni) and chromium (Cr), which may pose a risk to marine biota during a gigaton-scale ESW application. Herein we derive a first guideline for coastal olivine dispersal based on existing marine environmental quality standards (EQS) for Ni and Cr. Results show that benthic biota are at the highest risk when olivine and its associated trace metals are mixed in the surface sediment. Specifically, depending on local sedimentary Ni concentrations, 0.059-1.4 kg of olivine m^-2 of seabed could be supplied without posing risks for benthic biota. Accordingly, globally coastal ESW could safely sequester only 0.51-37 Gt of CO₂ in the 21st century. On the basis of current EQS, we conclude that adverse environmental impacts from Ni and Cr release could reduce the applicability of olivine in coastal ESW. Our findings call for more in-depth studies on the potential toxicity of olivine toward benthic marine biota, especially in regard to bioavailability and metal mixture toxicity.

Assessment of optimal conditions for the performance of greenhouse gas removal methods

In this study, a comparative literature-based assessment of the impact of operational factors such as climatic condition, vegetation type, availability of land, water, energy and biomass, management practices, cost and soil characteristics was carried out on six greenhouse gas removal (GGR) methods. These methods which include forestation, enhanced weathering (EW), soil carbon sequestration (SCS), biochar, direct air capture with carbon storage (DACCS) and bioenergy with carbon capture and storage (BECCS) were accessed with the aim of identifying the conditions and requirements necessary for their optimum performance. The extent of influence of these factors on the performance of the various GGR methods was discussed and quantified on a scale of 0-5. The key conditions necessary for optimum performance were identified with forestation, EW, SCS and biochar found to be best deployed within the tropical and temperate climatic zones. The CCS technologies (BECCS and DACCS) which have been largely projected as major contributors to the attainment of the emission mitigation targets were found to have a larger locational flexibility. However, the need for cost optimal siting of the CCS plant is necessary and dependent on the presence of appropriate storage facilities, preferably geological. The need for global and regional cooperation as well as some current efforts at accelerating the development and deployment of these GGR methods were also highlighted.

Exploring cross-national public support for the use of enhanced weathering as a land-based carbon dioxide removal strategy

This study explores how public attitudes across three countries influence support towards terrestrial enhanced weathering, whereby silicate minerals are applied to agricultural land to remove carbon dioxide from the atmosphere. An online survey was administered in Australia (N = 1000), the UK (N = 1000), and the USA (N = 1026) where there are ongoing field trials of this technique. Findings are similar across all three countries with many participants unfamiliar with enhanced weathering and unsure about supporting the use of enhanced weathering. Results show that positive affect is the main predictor for support of this technique, along with perceived benefits and level of concern about climate change. Open-ended questions asking why respondents would or would not support the use of enhanced weathering elicit mainly affective concepts, with enhanced weathering seen by individual respondents as either something mainly positive or mainly negative, with others saying it sounds risky and/or would have impacts on the environment. The way in which enhanced weathering is communicated is likely to influence support of the use of this strategy so must be undertaken carefully. Overall, our findings show that it is imperative to continue to engage the public, thereby allowing their views to be incorporated as enhanced weathering technology develops over time.

Contrasting bacterial communities and their assembly processes in karst soils under different land use

Structure and assembly processes of soil bacterial communities under different land use at karst areas remained poorly understood to date. To address this issue, soil samples from arable land and pristine forest over a karst cave, located in the acid rain impacted area, Hubei province, were collected and subjected to high-throughput sequencing and multivariate statistical analysis. Bacterial communities and functions remarkably distinguished between soils under different land use. Both edaphic properties (the content of SO₄^2-, C/N, pH, TN) and weathering processes, such as Si concentration, Mg/Al and Ca/Al, significantly impacted on soil bacterial community structures. Variable selections were predominant ecological processes, and pH and SO₄^2- concentration were of significance in community assembly. Random molecular ecological network analysis revealed a more stable and complex microbial network in the forest ecosystem, which can quickly response to environmental change. Forest soil bacteria were mainly phototrophs, involving in C and N cycles, whereas those in arable soils were mainly chemoheterotrophs, capable of degrading organic fertilizers due to anthropogenic activities as confirmed by the analysis of keystone taxa, indicators and functional prediction. These results reveal that land use constructed soil bacterial communities in different aspects such as the structure, potential functions, microbial interactions and correlations with environmental variables. To our knowledge, this is the first report on bacterial community assembly in karst soils under different land use which enhances our understanding about how land use impact on microbial interaction and community assembly processes.

Increased yield and CO2 sequestration potential with the C4 cereal Sorghum bicolor cultivated in basaltic rock dust-amended agricultural soil

Land-based enhanced rock weathering (ERW) is a biogeochemical carbon dioxide removal (CDR) strategy aiming to accelerate natural geological processes of carbon sequestration through application of crushed silicate rocks, such as basalt, to croplands and forested landscapes. However, the efficacy of the approach when undertaken with basalt, and its potential co-benefits for agriculture, require experimental and field evaluation. Here we report that amending a UK clay-loam agricultural soil with a high loading (10 kg/m² ) of relatively coarse-grained crushed basalt significantly increased the yield (21 ± 9.4%, SE) of the important C₄ cereal Sorghum bicolor under controlled environmental conditions, without accumulation of potentially toxic trace elements in the seeds. Yield increases resulted from the basalt treatment after 120 days without P- and K-fertilizer addition. Shoot silicon concentrations also increased significantly (26 ± 5.4%, SE), with potential benefits for crop resistance to biotic and abiotic stress. Elemental budgets indicate substantial release of base cations important for inorganic carbon removal and their accumulation mainly in the soil exchangeable pools. Geochemical reactive transport modelling, constrained by elemental budgets, indicated CO₂ sequestration rates of 2-4 t CO₂ /ha, 1-5 years after a single application of basaltic rock dust, including via newly formed soil carbonate minerals whose long-term fate requires assessment through field trials. This represents an approximately fourfold increase in carbon capture compared to control plant-soil systems without basalt. Our results build support for ERW deployment as a CDR technique compatible with spreading basalt powder on acidic loamy soils common across millions of hectares of western European and North American agriculture.

Negative emissions technologies: A complementary solution for climate change mitigation

Carbon dioxide (CO₂) is the main greenhouse gas (GHG) and its atmospheric concentration is currently 50% higher than pre-industrial levels. The continuous GHGs emissions may lead to severe and irreversible consequences in the climate system. The reduction of GHG emissions may be not enough to mitigate climate change. Consequently, besides carbon capture from large emission sources, atmospheric CO₂ capture may be also required. To meet the target defined for climate change mitigation, the removal of 10 Gt·yr^-1 of CO₂ globally by mid-century and 20 Gt·yr^-1 of CO₂ globally by the end of century. The technologies applied with this aim are known as negative emission technologies (NETs), as they lead to achieve a negative balance of carbon in atmosphere. This paper aims to present the recent research works regarding NETs, focusing the research findings achieved by academic groups and projects. Besides several advantages, NETs present high operational cost and its scale-up should be tested to know the real effect on climate change mitigation. With current knowledge, no single process should be seen as a solution. Research efforts should be performed to evaluate and reduce NETs costs and environmental impact.

Farming with crops and rocks to address global climate, food and soil security

The magnitude of future climate change could be moderated by immediately reducing the amount of CO₂ entering the atmosphere as a result of energy generation and by adopting strategies that actively remove CO₂ from it. Biogeochemical improvement of soils by adding crushed, fast-reacting silicate rocks to croplands is one such CO₂-removal strategy. This approach has the potential to improve crop production, increase protection from pests and diseases, and restore soil fertility and structure. Managed croplands worldwide are already equipped for frequent rock dust additions to soils, making rapid adoption at scale feasible, and the potential benefits could generate financial incentives for widespread adoption in the agricultural sector. However, there are still obstacles to be surmounted. Audited field-scale assessments of the efficacy of CO₂ capture are urgently required together with detailed environmental monitoring. A cost-effective way to meet the rock requirements for CO₂ removal must be found, possibly involving the recycling of silicate waste materials. Finally, issues of public perception, trust and acceptance must also be addressed.

Simulating carbon capture by enhanced weathering with croplands: an overview of key processes highlighting areas of future model development

Enhanced weathering (EW) aims to amplify a natural sink for CO2 by incorporating powdered silicate rock with high reactive surface area into agricultural soils. The goal is to achieve rapid dissolution of minerals and release of alkalinity with accompanying dissolution of CO2 into soils and drainage waters. EW could counteract phosphorus limitation and greenhouse gas (GHG) emissions in tropical soils, and soil acidification, a common agricultural problem studied with numerical process models over several decades. Here, we review the processes leading to soil acidification in croplands and how the soil weathering CO2 sink is represented in models. Mathematical models capturing the dominant processes and human interventions governing cropland soil chemistry and GHG emissions neglect weathering, while most weathering models neglect agricultural processes. We discuss current approaches to modelling EW and highlight several classes of model having the potential to simulate EW in croplands. Finally, we argue for further integration of process knowledge in mathematical models to capture feedbacks affecting both longer-term CO2 consumption and crop growth and yields.