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Katharine Maher
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Reactive transport modeling of soil-based carbon removal: from reactive interfaces to objective limits
Achieving the temperature goals of the Paris Agreement will require 100 to 300 gigatons of carbon dioxide removal (CDR) this century. As large-scale interventions become central to climate planning, distinguishing between temporary carbon fluxes and durable atmospheric removals is essential. Yet the absence of robust and efficient monitoring, reporting and verification (MRV) frameworks remains a critical barrier for investment, policy progress and market development. Reactive transport models (RTMs) are often viewed as too complex, uncertain or immature to underpin MRV, despite their unique potential to enable uncertainty quantification, data assimilation and harmonization of discrepant fluxes. This tension highlights a broader challenge in carbon markets: how should scientific models be incentivized, governed and trusted as part of financial and regulatory infrastructure?
Using enhanced weathering (EW) as a case study, this lecture examines how mechanistic models can illuminate the coupled physical and chemical processes that govern CDR. MRV for EW requires translating mineral dissolution into durable atmospheric drawdown, as a function of coupled gas and aqueous transport, surface pH buffering, and dissolution-precipitation processes in variably saturated porous media and over scales spanning soils to estuaries. For the soil zone, new frameworks for surface proton buffering and the development of “reaction tags” identify mechanistic limits to verifiable carbon sequestration that arise from inefficiencies in alkalinity generation and export. Model-based analysis also establishes a physical basis for reconciling discrepancies between feedstock dissolution inferred from solid-phase measurements and the lack of measurable aqueous carbon export, a harmonization critical for robust MRV. Together, these examples illustrate both the diagnostic power of mechanistic modeling and the current limitations in parameterization, data integration, and multiphysics representations that constrain the readiness of models for decision support.
The talk concludes by expanding to other soil-based CDR pathways and raising emerging questions around model governance: What constitutes “fit-for-purpose” modeling in carbon markets, and how should model-based evidence be evaluated when used to substantiate claims of durable CO₂ removal?
Interview with Katharine Maher
- Your research spans geochemistry and climate—how do porous media fit into that picture?
All carbon cycling takes place in porous media, including long-term chemical weathering and highly engineered carbon dioxide removal. Effectively, it is a critical interface between carbon in the atmosphere and the storage reservoirs of the biosphere and geosphere. As we move towards large-scale carbon dioxide removal, porous media is central.
- What new insights are we gaining about mineral-fluid interactions and the carbon cycle?
The need to quantify carbon fluxes with greater temporal and spatial resolution, and with defined uncertainty, is increasingly urgent as carbon policy and carbon markets expand. We are learning that measuring mineral-fluid interactions and corresponding carbon fluxes at the precision desired by the marketplace is challenging and expensive. This is motivating the development of new tools and approaches.
- What tools or approaches are reshaping research in your field?
Reactive transport models have long been an important tool for interrogating fluid-mineral interactions, but I am excited about integration with other approaches from data science to machine learning/AI that can help us to interrogate the knowledge encoded in increasingly complex models.
- How can the porous media community contribute to climate solutions?
Science and engineering expertise is critical to ensuring that carbon dioxide removal strategies achieve atmospheric outcomes. In addition to continued emphasis on the physics and chemistry problems, critical technical review of climate claims by companies and countries is increasingly urgent.
- What do you hope to gain from engaging with the InterPore audience?
The convergence of science with markets highlights the continued existence of grand challenges involving porous media, from understanding the discrepancies between laboratory and field rates, to the mixing of solutes in complex porous media, to the dynamics of protons and other ions at interfaces. I am excited to learn about continual advances that improve our understanding of these processes, as well as to learn about translational efforts that might enable these advances to transition into practice.
About Katharine Maher
Kate Maher is a Professor of Earth System Science at Stanford University and a Senior Fellow at the Woods Institute for the Environment. Dr. Maher’s work integrates field data, advanced computational models, and machine learning approaches to advance the sustainable engineering of earth systems, including soil-based carbon dioxide removal, water management, and carbon cycling in soil. Over two decades of research, she has developed methods to quantify enhanced weathering processes, greenhouse gas fluxes in soils, and subsurface carbon storage and mineralization, addressing global challenges in carbon and water management. Central to this work has been the creation of data science tools that combine scientific models with decision-making frameworks. She is a recipient of the James B. Macelwane Medal, a Fellow of the American Geophysical Union, and is recognized for her work on the carbon cycle in a permanent exhibit in the Smithsonian Museum of Natural History. Kate received her B.A. from Dartmouth College in Environmental Earth Science, an M.S. in Civil and Environmental Engineering from U.C. Berkeley, and a Ph.D. in Earth and Planetary Sciences also from U.C. Berkely. Prior to joining the faculty at Stanford, she was a Mendenhall Postdoctoral Fellow with the U.S. Geological Survey.
