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Following on from parts 1 and 2 of our Theme 1 summary, see some of the work our modellers got up to from mid-2021 to mid-2023, including the papers we published during this period. Check back soon for our 2024 update.

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2021-2022

Substantial carbon removal potential of enhanced rock weathering of UK croplands

2022-2023

Transforming U.S. agriculture with crushed rock for CO₂ sequestration and increased production

Model intercomparison and timescales of CDR

Air Quality and Atmospheric Composition Modelling Experiments

2021-2022

Substantial carbon removal potential of enhanced rock weathering of UK croplands

Our recent publication by Kantzas et al. (2022) presents a comprehensive analysis of deploying enhanced rock weathering (ERW) as a carbon removal strategy in UK croplands. This interdisciplinary endeavor engaged researchers from three LC3M research themes, highlighting the collaborative effort needed to tackle complex modelling challenges. The study garnered substantial attention, with coverage in 71 news outlets and widespread discussion on social media platforms.

Using dynamic carbon budget modelling, we evaluated the carbon dioxide removal potential, costs, and agricultural benefits associated with implementing ERW strategies across arable croplands in the UK. Our findings reveal that ERW holds significant promise, with the potential to remove 6–30 MtCO₂ per year by 2050. This amount represents up to 45% of the total atmospheric carbon removal required nationally to achieve net-zero emissions. These results underscore the pivotal role ERW could play in national climate mitigation strategies, provided it receives acceptance amongst society and stakeholders.

Beyond carbon removal, ERW offers a range of co-benefits. Notably, it can substantially mitigate emissions of nitrous oxide, the third most significant greenhouse gas, while also contributing to the widespread reversal of soil acidification. Thus, ERW implementation could lead to considerable cost savings through reduced fertiliser usage in agricultural practices.

Our analyses not only provide valuable insights for the UK but also serve as a guide for other nations seeking to pursue carbon dioxide removal initiatives and decarbonise their agricultural sectors. By embracing ERW as part of their climate strategies, countries can move closer to achieving their emissions reduction goals while simultaneously enhancing agricultural sustainability.

2022-2023

Transforming US agriculture with crushed rock for CO₂ sequestration and increased production

The United States is striving to achieve net-zero greenhouse gas emissions by 2050, a goal that involves decarbonising the energy sector and deploying carbon dioxide removal (CDR) technologies. Among these technologies, ERW emerges as a promising yet underexplored solution

Our USA study delves into the potential of EW across the continental United States, accounting for the sensitivity of CDR and ERW to rock feedstocks with different reactivities. To accomplish this, Lyla crafted mineralogies arising from thousands of geochemical samples, and Euripides developed novel clustering methods to determine the range of mineralogies which are likely to be delivered from mines to agricultural land. With this upgraded modelling framework, we estimated that ERW could sequester 0.2-0.3 billion metric tons of CO₂ annually, fulfilling 30-60% of the U.S.'s engineered CDR targets by 2050. The associated costs were approximated to be $100-150 per tonne of CO₂, making ERW economically viable in the next two decades.

This research extended beyond mere sequestration. Collaborating with US experts in river geochemistry, they demonstrated that rivers could safely transport weathered products without CO₂ re-release. Moreover, treating crops in the U. Corn Belt with basalt led to estimates of reduced emissions of the greenhouse gas N₂O and decreased tropospheric O₃ pollution, potentially resulting in enhanced crop yields.

We also assessed public acceptance of ERW and its social license to operate. In principle, EW deployment could bring significant economic and community benefits for both quarrying and agricultural states, especially in agricultural communities where crushed rocks like limestone are already applied to fields. This widespread practice demonstrates farmers' willingness to embrace soil pH management for enhanced productivity and soil health.

Transitioning to ERW presents a feasible option for large-scale farming innovation to combat climate change while bolstering food, soil, and biofuel security. The study concludes that with existing supply chains, ERW offers a straightforward technological pathway to permanent atmospheric carbon sequestration, aligning with US net-zero objectives.

Model intercomparison and timescales of CDR

Lyla's current focus is to unravel the dynamics of carbon export, aiming to quantify lag times accurately. Lag times arise when soil cation exchange processes temporarily delay the export of cations and bicarbonate ions to rivers, leading to longer timescales for CDR. This insight is crucial for improving the effectiveness of geochemical models designed to capture carbon through enhanced weathering. Preliminary work on this emerging topic was done for for the ERW-CDR Model Intercomparison Project (RockMIP), an initiative that Lyla is actively organising with collaborators at Yale and Georgia Tech. The goal of RockMIP is to evaluate the fitness of various models for their intended purpose, especially considering their integration into the Monitoring, Reporting, and Verification (MRV) process.

Benchmarking ERW models against diverse datasets is a core objective of RockMIP, aiding in understanding how different models compare and perform against one another. Early participants in this initiative include colleagues from Yale University and the Georgia Institute of Technology. By collaborating on this scale, we ensure that the models we develop are robust, reliable, and aligned with the rigorous standards required for accurate assessment and monitoring of enhanced rock weathering processes. Watch this space for a RockMIP website coming soon!

Air Quality and Atmospheric Composition Modelling Experiments

Maria conducted air quality simulations as part of the ERW modelling study in the US. Using an Earth system model (CESM2.2), she evaluated the potential unintended air quality impacts of basalt application in crops. ERW has been observed to increase soil pH, which could lead to increased emissions of ammonia (NH₃) due to ammonia volatilisation at higher pH levels. Although EW suppresses soil nitric oxide (NO) emissions, both NO and NH₃ contribute to the formation of fine particulate matter (particles < 2.5μm in diameter; PM2.5). NH₃ reacts with nitric acid to create secondary inorganic nitrate and ammonium aerosols, thereby contributing to PM2.5 production.

Her findings indicated that by 2070, ERW could increase soil NH₃ emissions by 4-6%.  However, the reduction in soil NO emissions limits the production of nitric acid, leading to a decrease in the formation of secondary inorganic nitrate and ammonium aerosols. As a result, this modelling exercise estimated a 5% reduction in spring and summertime PM2.5 levels by 2070. This suggested that ERW could effectively mitigate future PM2.5 formation in agricultural regions, aligning with efforts to reduce nitrogen oxide emissions and control PM2.5 levels, particularly in areas such as California.

In addition, her work found that widespread basalt application for ERW unintentionally reduces emissions of N₂O, a potent greenhouse gas and crucial component for stratospheric ozone. With chlorinated species declining in the stratosphere due to the Montreal Protocol, N₂O is projected to become the primary ozone-depleting substance after the mid-century. While the benefits of reducing N₂O emissions for climate and stratospheric ozone recovery are acknowledged, the specific impact remains uncertain, depending on the background atmospheric composition and climate conditions.

To address this uncertainty, James Weber, a postdoc working with Maria, initiated a series of Earth system model experiments to simulate sustained reductions in N₂O emissions achieved through ERW and other agriculture abatement strategies. These simulations considered various climate change mitigation scenarios and aimed to provide policy-relevant insights into the advantages of N₂O emissions reduction through ERW compared to idealised model experiments simulating abrupt changes in N₂O levels.

And there’s 8 years’ worth of modelling work summed up – do stay tuned for our (much shorter) annual update from Theme 1’s work over 2023-2024, coming soon!