What could be more festive than carbon storage in snowy evergreen forests?

@geoengineering1 interviews Kevin Bradley D'Souza, a postdoctoral researcher at the University of Waterloo, about the real climate potential of reforesting Boreal forests. Kevin explains the crucial role these forests play in carbon storage, biodiversity, and permafrost protection, while noting that reforestation in the Boreal comes with important challenges. The conversation explores key factors such as albedo effects, wildfire risks, and the importance of Indigenous perspectives in forest management. Kevin also stresses the need for careful, multi-dimensional approaches to reforestation and urges caution around commercial forest-based carbon credits, given the scientific uncertainties that still remain.

Papers discussed:

Dsouza, K. B., Ofosu, E., Salkeld, J., Boudreault, R., Moreno-Cruz, J., & Leonenko, Y. (2025). Assessing the climate benefits of afforestation in the Canadian Northern Boreal and Southern Arctic. Nature Communications, 16(1), 1964. https://doi.org/10.1038/s41467-025-56699-9

Dsouza, K. B., Ofosu, E., Boudreault, R., Moreno-Cruz, J., & Leonenko, Y. (2025). Substantial carbon removal capacity of Taiga reforestation and afforestation at Canada’s boreal edge. Communications Earth & Environment, 6(1), 893. https://doi.org/10.1038/s43247-025-02822-z

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Miranda Hack provides an in-depth look at the often-overlooked engineering and logistical barriers to large-scale deployment of solid particles for stratospheric aerosol injection (SAI). She explains how dispersing sub-micron mineral particles at altitude, including challenges like agglomeration, complex nozzle flows, and supply-chain constraints, introduces significant uncertainties and costs. These challenges may reduce cooling efficiency and narrow the design space for “low-risk” SAI strategies, suggesting that solid aerosols could be far less viable than existing models assume.

Paper: Hack, M., McNeill, V. F., Steingart, D., & Wagner, G. (2025). Engineering and logistical concerns add practical limitations to stratospheric aerosol injection strategies. Scientific Reports, 15(1), 34635. https://doi.org/10.1038/s41598-025-20447-2

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Roderick Hyde discusses his recent paper on using high-altitude hoses for solar geoengineering. While most proposals focus on aircraft delivery, Hyde revisits an older but largely dismissed concept. He describes suspending a 20 km hose by balloons to continuously pump sulfur-bearing fluids into the stratosphere, and argues that advances in modern materials and engineering may overcome past barriers.

The conversation covers the technical hurdles such as wind dynamics, hose stability, extreme pressures, and material stress, as well as design variations for pumping H₂S as liquid or gas. Hyde explains how streamlining, intermediate pumps, and lightweight aero-shrouds could make the system viable.

The discussion also highlights the potential advantages of this approach, including affordability, continuous operation, and scalability. While a single hose could not halt global warming, Hyde suggests that a distributed network of ~20 installations could offset warming from CO₂, offering a near-term, low-cost option to buy time while longer-term climate solutions take effect.

Paper: Hyde, R. A. (2025). A Planetary Cooling Hose. arXiv preprint arXiv:2509.07985. https://doi.org/10.48550/arXiv.2509.07985

John Moore joins the podcast to discuss his recent Viewpoint article responding to Siegert et al.’s paper on polar geoengineering. While Siegert and colleagues argue that proposed interventions are infeasible, environmentally dangerous, and a distraction from decarbonization, Moore contrasts the prevailing “consequences-based paradigm” (raising alarms to spur actions) with a new “compassionate harm reduction paradigm” that calls for exploring all potential tools including geoengineering rather than rejecting them outright, so humanity has options to reduce harm if warming overshoots.

The conversation covers the risks of melting glaciers and sea-level rise, and specific concepts such as stratospheric aerosol injection. Moore also stresses the importance of Arctic Indigenous leadership, pointing to Saami Council-led review processes as a model for rights-based and knowledge co-produced governance.

The discussion also highlights the sharp divides in the climate community over polar geoengineering and raises fundamental questions about the responsibilities of scientists in an era of accelerating climate risk.

Papers:

Lead Article: Siegert, M., Sevestre, H., Bentley, M. J., Brigham-Grette, J., Burgess, H., Buzzard, S., ... & Truffer, M. (2025). Safeguarding the polar regions from dangerous geoengineering: a critical assessment of proposed concepts and future prospects. Frontiers in Science, 3, 1527393. https://doi.org/10.3389/fsci.2025.1527393

Viewpoint: Moore, J. C., Macias-Fauria, M., & Wolovick, M. (2025). A new paradigm from the Arctic. Frontiers in Science, 3, 1657323. https://doi.org/10.3389/fsci.2025.1657323

Jacob Bronsther & Yangyang Xu discuss their recent paper on the socioeconomic costs of Solar Radiation Modification. While SRM’s direct technical costs appear modest (~$18B/°C cooling), the authors argue that its broader costs are far greater. They estimate that Stratospheric Aerosol Injection could generate between $0 and $809 billion annually in side-effect harms, with potentially higher figures for Marine Cloud Brightening.

The conversation also explores SRM’s reliance on unprecedented global cooperation, the political risks of weather accountability, and the dangers of termination, which could impose major financial costs. They contrast these challenges with large-scale Carbon Dioxide Removal, noting that although CDR entails immense technical expenses, it avoids some of SRM’s political and termination risks.

The discussion highlights the complexity of weighing the full spectrum of costs and benefits when evaluating climate-engineering strategies.

Paper: Bronsther, J., & Xu, Y. (2025). The social costs of solar radiation management. npj Climate Action, 4(1), 69. https://doi.org/10.1038/s44168-025-00273-y

Brian Soden discusses his recent study on injecting absorptive aerosols, such as black carbon, into the upper stratosphere to weaken the CO₂ greenhouse effect.

The conversation addresses the radiative physics underpinning this concept, its potential cooling efficiency relative to conventional scattering aerosols, and associated environmental risks. While model results indicate the method could theoretically be effective, Soden remains sceptical about its practical viability.

Paper: He, H., Soden, B. J., Vecchi, G. A., & Yang, W. (2025). Stratospheric aerosol injection can weaken the carbon dioxide greenhouse effect. Communications earth & environment, 6(1), 485. https://doi.org/10.1038/s43247-025-02466-z

Daniel Bodansky discusses his recent article on the drawbacks of a global moratorium on solar radiation management deployment.

The conversation critiques whether a moratorium is feasible or effective, arguing it could hinder critical research, be difficult to enforce, and unintentionally become a proxy for a permanent ban. Instead, the discussion highlights the need for more research and stronger governance frameworks to better understand and responsibly manage geoengineering.

Article: Biniaz, S., & Bodansky, D. (2025, May 13). Why a global “moratorium” on solar radiation management deployment should get a chilly reception. Just Security. https://www.justsecurity.org/113295/moratorium-srm-deployment-chilly-reception/

Diego Villanueva discusses his paper on mixed-phase regime cloud thinning (MCT). This geoengineering approach involves using ice-nucleating particles to reduce the heat-trapping effects of polar clouds.

Using climate and cloud-resolving models, the study finds MCT could offset up to 25% of polar ocean warming from CO₂ doubling and increase sea ice by 8% in the Arctic and 14% in Antarctica. In the podcast, we discuss the science behind this method, its potential benefits, limitations, and broader implications.

Paper: Villanueva, D., Possner, A., Neubauer, D., Gasparini, B., Lohmann, U., & Tesche, M. (2022). Mixed-phase regime cloud thinning could help restore sea ice. Environmental Research Letters, 17(11), 114057. https://doi.org/10.1088/1748-9326/aca16d