Reviewer 2 does geoengineering

Cornell University geochemist Louis Derry joins @geoengineering1 to discuss a fundamental question for enhanced rock weathering: how much of the alkalinity generated in soils actually makes it through watersheds to the ocean? Derry argues that many studies and commercial MRV approaches focus on the top 10-30 cm of soil, potentially missing critical processes along the full flow path, including ion exchange in acidic soils, secondary clay formation, acidity generation and carbonate precipitation, which can reduce alkalinity export before it reaches streams. He highlights hydrological constraints, arguing that limited runoff and realistic alkalinity concentrations make proposed removal rates of 5-10 tonnes of CO₂ per hectare per year difficult to achieve across typical row-crop regions. Drawing on natural basaltic catchments and experimental systems, he points to estimates of global basalt weathering of ~0.1-0.2 Gt CO₂/yr, suggesting gigaton-scale enhanced weathering projections are overoptimistic, with co-benefits more credible than large-scale CDR. Paper Discussed: Derry, L. A., Maher, K., & Chadwick, O. A. (2026). Critical zone processes limit alkalinity export from natural basaltic systems. Nature, 1–6. https://doi.org/10.1038/s41586-026-10936-3 Related article: Limitations on carbon dioxide uptake by enhanced weathering - Springer Nature Research Communities https://communities.springernature.com/posts/limitations-on-carbon-dioxide-uptake-by-enhanced-weathering

@geoengineering1 interviews Claudia Elisabeth Wieners and Meike de Nooij about extratropical cyclones, the winter storm systems that drive much of the weather variability and many extreme wind and precipitation events in the midlatitudes, and how stratospheric aerosol injection (SAI) could alter their tracks and associated weather extremes. They discuss what makes extratropical cyclones different from tropical cyclones, why SAI could affect storm tracks, and what their high-resolution modelling reveals about changes in the North Atlantic and North Pacific. The conversation explores why SAI is not simply an “undo button” for global warming, with regional shifts in storm tracks and different responses in precipitation and wind extremes even when global temperatures are brought closer to present-day levels. Claudia and Meike also discuss the uncertainties surrounding their findings, the need for further high-resolution modelling, and the broader challenges of assessing and governing SAI. They argue that governments and policymakers need to take SAI seriously by supporting rigorous research and considering how any future deployment should be carefully governed. Paper discussed: de Nooij, M., de Jong, J., Baatsen, M. L., & Wieners, C. E. (2026). Extratropical Cyclone and Storm track Responses to Stratospheric Aerosol Injection in High-Resolution CESM Simulations. EGUsphere [preprint], 1-26. https://doi.org/10.5194/egusphere-2026-4133

Could reducing sunlight to cool the planet also affect mental health? @geoengineering1 interviews Shinsuke Tanaka about new research examining the link between sunlight and suicide and what it could mean for solar radiation management (SRM). Using nearly three decades of U.S. county-month data, Tanaka and colleagues find that sustained reductions in sunlight significantly increase suicide rates. They estimate that a 1.5°C SRM scenario could result in around 3,810 additional U.S. suicides between 2030 and 2100 from reduced sunlight alone, or 16,320 when temperature effects are included. The conversation also covers the difference between seasonal correlations and causal effects, possible biological and behavioral mechanisms, and the challenges of applying U.S.-based findings globally. Paper Discussed: Tanaka, S., & Matsubayashi, T. (2026). Clouding the mind? Assessing the suicide impacts of solar radiation management in the United States. The Japanese Economic Review, 1-21. https://link.springer.com/article/10.1007/s42973-026-00273-5

How much carbon can enhanced rock weathering actually remove? In this episode, @geoengineering1 talks with Tyler Kukla of CarbonPlan about how assumptions about rock surface roughness can dramatically change enhanced weathering estimates. They discuss why surface area is critical to weathering rates, how commonly used roughness calculations can overestimate available surface area, and what this means for modeled CO₂ removal. The conversation also explores the differences between surface-area- and water-transport-limited weathering, the challenges of scaling enhanced weathering, and why better measurements are needed to constrain models. The discussion is based on Tyler Kukla et al.’s CarbonPlan article, How Surface Roughness Scaling Can Mislead Enhanced Weathering Predictions. https://carbonplan.org/research/modeling-bytes-02-roughness

@geoengineering1 interviews Taveen Kapoor about his study [preprint] showing that purely scattering stratospheric aerosols can produce positive shortwave radiative forcing, and localized warming, over high-albedo surfaces such as snow, ice, and deserts. They discuss how diffuse light reflected from bright surfaces travels farther through the aerosol layer, increasing the likelihood of backscattering toward the surface. They also discuss why multi-angle radiative-transfer calculations reveal stronger positive forcing than the standard two-stream approximation, particularly in tropical and extratropical regions, while daily averages can obscure intense daytime forcing peaks. The conversation explores implications for SAI, including potential effects on snowmelt and regions such as the Tibetan Plateau and Sahel, as well as the growing burden of alumina aerosols from spacecraft reentry. They also discuss uncertainties and related research on alumina-based stratospheric aerosols. Paper Discussed: Zhang, L., Kapoor, T. S., Upadhyay, P., & Chakrabarty, R. K. (2026). Purely light-scattering aerosols could induce positive shortwave radiative forcing over high-albedo surfaces. EGUsphere, 2026, 1-17. https://doi.org/10.5194/egusphere-2026-3947