| SOLAR GEOENGINEERING WEEKLY SUMMARY (13 JANUARY 2024 - 19 JANUARY 2024)
DEADLINES
RESEARCH PAPERSDommo, A., Nkrumah, F., Quagraine, K, A., Klutse, N. A. B., Quenum, G, M, L, D. (2025). Assessing the response of surface cloud radiative effects to Stratospheric Aerosol Injection over West and Central Africa. ESS Open ArchiveAbstractSolar radiation management with stratospheric aerosol injection has been proposed as a potential mechanism to mitigate global warming and prevent it from reaching the tipping point. This study investigates the response of surface cloud radiative effects (CREs) to stratospheric aerosol injection (SAI) relative to Shared Socio-Economic Pathways (SSP2-4.5) across three regions: southern West Africa (SWA), Central Africa (CA) and the Sahara (SA). We utilize simulations from the Community Earth System Model version 2 (CESM2) with the Whole Atmosphere Community Climate Model version 6 (WACCM6) under SAI deployment, comparing the outputs to those from the SSP2.4-5 scenario, which aligns with current climate policy scenarios. The findings indicate that SAI has the potential to mitigate the decreasing trend of shortwave cloud cooling by -0.7W/m², -0.81W/m², -0.17W/m², while enhancing the longwave warming by +1.11W/m², +0.65W/m² and +0.31W/m², over CA, SWA, and SA, respectively. However, it is important to note that these observed changes may be attributable to natural variability rather than the direct effects of SAI, and should be taken with caution. An exception is the longwave cloud warming, which exhibits robust changes over CA. The results also reveal that changes in shortwave cloud cooling effect demonstrate high sensitivity to changes in liquid water path whereas changes in longwave cloud warming tend to exhibit greater sensitivity to variations in cloud fraction. It is noteworthy that current simulations involving SAI lack sufficient variables to facilitate comprehensive comparisons among different outputs.
Talati, S., Buck, H. J., & Kravitz, B. (2025). How to address solar geoengineering’s transparency problem. Proceedings of the National Academy of Sciences, 122(3), e2419587122.AbstractIn 2010, climate scientists gathered at the Asilomar Conference Center in California, in a convening that echoed a legendary 1975 meeting in which a scientific committee came together in a exercise of self-governance to create guidelines for recombinant DNA, which many at the time feared could have unintended negative impacts on the environment and possibly on human health. The climate scientists 15 years ago had a similar ethical challenge: to provide research principles for solar geoengineering. They realized that the idea of deliberately reflecting a small fraction of incoming sunlight to cool Earth would require higher levels of trust and governance than other kinds of climate research. Climate journalist Jeff Goodell, who attended the 2010 meeting, noted that he may have “witnessed the birth of something new—call it the conscience of a geoengineer”.Despite the consensus of the scholarly literature (see SI Appendix, Table S1 for a summary of the numerous discussions on principles and codes of conduct in geoengineering), there are still no established practices around transparency, let alone regulations demanding it. Rather, we have the opposite: private companies such as Make Sunsets, a US-based company that sells “cooling credits” and has been releasing toxic sulfur balloons (2) since 2022, or Stardust, the Israeli startup with $15 million of venture capital funding (3). Few seem to know quite what they are doing. What happened to the conscience of the geoengineer?Decision-makers and members of the general public need to know that geoengineering research is legitimate, which means that findings are robust, contrary results aren’t hidden, and investigations are free from conflicts of interest. This applies as much to “outdoor” research as it does to modeling and laboratory work, where the idea of geoengineering is shaped. If people are going to evaluate whether to support research or even deployment, they want to know where the idea came from, who funded it, and who was or wasn’t at the table. This is how trust is built.
Brody, E., Zhang, Y., MacMartin, D. G., Visioni, D., Kravitz, B., & Bednarz, E. M. (2025). Using Optimization Tools to Explore Stratospheric Aerosol Injection Strategies. EGUsphere, 2025, 1-26.AbstractStratospheric aerosol injection (SAI), as a possible supplement to emission reduction, has the potential to reduce some of the impacts associated with climate change. However, the outcomes will depend on how it is deployed: not just how much, but the latitudes of injection and the distribution of injection rates across those latitudes. Different such strategies have been proposed, managing up to three climate metrics simultaneously by injecting at multiple latitudes. Nonetheless, these strategies still do not fully compensate for the pattern of climate changes caused by increased greenhouse gas concentrations, creating a novel climate state. To date there has not been a systematic assessment of whether there are strategies that could do a better job of managing some specific climate goals, nor an assessment of any underlying trade-offs between managing different sets of climate goals. Herein we use existing climate model simulations of the response to injection at 7 different latitudes, and apply optimization tools to explore the limitations and trade-offs when designing strategies that combine injection across these latitudes. This relies on linearity being a sufficiently good assumption, which we first validate. The resulting "best"' strategy of course depends on what goals are being optimized for. For example, at 1 degree Celsius of cooling, we predict that there exist strategies that do a better job than those simulated to date at simultaneously balancing regional temperature and precipitation responses, but the differences may be too small to detect at lower levels of cooling.
Zhang, J., Chen, Y.-S., Gryspeerdt, E., Yamaguchi, T., & Feingold, G. (2020). Radiative forcing from the 2020 shipping fuel regulation is large but hard to detect. Communications Earth & Environment.AbstractReduction in aerosol cooling unmasks greenhouse gas warming, exacerbating the rate of future warming. The strict sulfur regulation on shipping fuel implemented in 2020 (IMO2020) presents an opportunity to assess the potential impacts of such emission regulations and the detectability of deliberate aerosol perturbations for climate intervention. Here we employ machine learning to capture cloud natural variability and estimate a radiative forcing of +0.074 ±0.005 W m−2 related to IMO2020 associated with changes in shortwave cloud radiative effect over three low-cloud regions where shipping routes prevail. We find low detectability of the cloud radiative effect of this event, attributed to strong natural variability in cloud albedo and cloud cover. Regionally, detectability is higher for the southeastern Atlantic stratocumulus deck. These results raise concerns that future reductions in aerosol emissions will accelerate warming and that proposed deliberate aerosol perturbations such as marine cloud brightening will need to be substantial in order to overcome the low detectability.
Chile Baldoni, T., Reboita, M. S., Machado Crespo, N., Ribeiro, J. G. M., & da Rocha, R. P. (2025). South Atlantic subtropical anticyclone responses to stratospheric aerosol injection. Environmental Research: Climate.AbstractThe South Atlantic Subtropical Anticyclone (SASA) is a key component of large-scale atmospheric circulation and is responsible for driving the climate in eastern Brazil and western Africa. Climate projections under warming scenarios suggest a strengthening, as well as a westward and southward expansion of this system. However, little is known about how the combination of global warming and climate intervention affects this system. To address this, SASA was identified from 2015 to 2099 in a set of projections with and without stratospheric aerosol injection (SAI). Projections were obtained from different initiatives: the Assessing Responses and Impacts of Solar Climate Intervention on the Earth System with Stratospheric Aerosol Injection (ARISE) using CESM2 global climate model, the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) using CESM1, and the Geoengineering Model Intercomparison Project (GeoMIP/G6sulfur) using MPI-ESM1-2-LR. As each project has its own specific model, scenario, SAI location, etc., no intercomparison was carried out among them. Instead, there is an indication of what occurs in each project when comparing the near (2040–2059) and the far future (2080–2099) projections under SAI and no-SAI scenarios. SASA under no-SAI scenarios, compared to the reference period (2015-2024), follows the pattern described in the literature, i.e., a tendency to be stronger and wider. However, these features are more evident in the GLENS project. This same project suggests that SAI scenarios contribute to reducing the impact of global warming on the SASA climatology, as SASA in the future acquires characteristics similar to those of the reference period. One of the possibilities for it is that GLENS has the largest SAI forcing, given that the goal was to cancel out the strong greenhouse gas-induced warming in RCP8.5.
REPORTS
WEB POSTS
UPCOMING EVENTSSolar Geoengineering Events Calendar
PODCASTSWhat is Stratospheric Aerosol Injection (SAI)? | Climate Reflections: The SRM360 Podcast | What is Stratospheric Aerosol Injection (SAI)? Climate Reflections: The SRM360 Podcast 22:09 |
"On June 15th, 1991, the densely populated island of Luzon in the Philippines awoke to an explosion that would turn out to be the second largest volcanic eruption of the 20th century. Mount Pinatubo had erupted, releasing a huge cloud of volcanic ash, hundreds of kilometers across and 40 kilometers high. As satellites tracked the ash cloud spread around the globe several times over, atmospheric scientists noted that over the next year, the Earth's global temperature had decreased by as much as half a degree Celsius. The eruption had added around 17 million tons of sulfur dioxide into the stratosphere, a layer of the atmosphere between 10 and 50 kilometers above the surface. And this sulfur had gone on to form countless tiny aerosol particles. In the lower atmosphere, these particles would have been washed out in days, but because the stratosphere is dry and stable, these particles lasted for several years, reflecting light, and cooling the Earth.Could the climate cooling effect of this eruption be replicated as a way to help tackle climate change? In this episode, we focus on the basics of the sunlight reflection method known as Stratospheric Aerosol Injection, or SAI, an SRM idea that looks like it could offer a practical means of halting or even reversing global warming within a few years. What is SAI? What would it take to cool the planet? And who could do it?Featuring Dr. Daniele Visioni, an Assistant Professor of Earth and Atmospheric Sciences at Cornell University and Dr. Joshua Horton, a Senior Program Fellow at the John F. Kennedy School of Government at Harvard University."
Can solar geoengineering fix the climate? | Storylines | Can solar geoengineering fix the climate? Storylines 26:48 |
"In an empty parking lot somewhere in northern California, Andrew Song and Luke Iseman inflate a balloon the size of a small car, full of sulfur dioxide. They will then launch the balloon high up into the stratosphere where it will pop, releasing its sulfur dioxide contents.Song and Iseman are the co-founders of Make Sunsets, a geoengineering startup that sells cooling credits. For a price, you can purchase a bit of the sulfur dioxide they’re pumping into these balloons and launching into the stratosphere, with the belief it will offset the warming effects of CO2.Because if you send enough sulfur dioxide into the stratosphere --- we’re talking a million tonnes a year --- it’ll significantly cool our warming planet. But the idea raises scores of complicated scientific and moral dilemmas.In this documentary, John Chipman goes to California to learn about the potential risks and benefits of solar geoengineering."
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