| SOLAR GEOENGINEERING WEEKLY SUMMARY (03 FEBRUARY 2024 - 09 FEBRUARY 2025)Subscribe to receive the monthly updates:
TABLE OF CONTENTS1. Research Papers2. Web Posts3. Reports4. Resources5. Upcoming Events6. Podcasts7. YouTube Videos
RESEARCH PAPERSFoster, R., Shumway, N., Harrison, D., & Fidelman, P. (2025). Governing marine cloud brightening for ecosystem conservation under a warming climate. Earth System Governance, 23, 100240.Abstract: Marine Cloud Brightening (MCB) is an emerging technology designed to mitigate the impacts of climate change by increasing the reflectivity of low-lying marine clouds. As research into this technology advances, the question of how to govern its trials and deployment becomes increasingly important. This paper identifies 12 challenges and 13 recommendations for governance of MCB, based on a systematic review of 27 publications. These findings are explored in relation to the design of effective MCB governance, with a particular focus on potential small-scale applications for ecosystem conservation purposes, like coral bleaching mitigation. The paper underscores the existing knowledge gaps and potential avenues for future MCB governance research, contributing to the burgeoning literature on the governance of innovative technologies aimed at addressing global environmental challenges. To manage potential risks and maximise potential benefits, it is crucial to understand the governance challenges MCB presents and explore options to address these challenges.
Hansen, J. E., Kharecha, P., Sato, M., Tselioudis, G., Kelly, J., Bauer, S. E., ... & Pokela, A. (2025). Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?. Environment: Science and Policy for Sustainable Development, 67(1), 6-44.Abstract: Global temperature leaped more than 0.4°C (0.7°F) during the past two years, the 12-month average peaking in August 2024 at +1.6°C relative to the temperature at the beginning of last century (the 1880-1920 average). This temperature jump was spurred by one of the periodic tropical El Niño warming events, but many Earth scientists were baffled by the magnitude of the global warming, which was twice as large as expected for the weak 2023-2024 El Niño. We find that most of the other half of the warming was caused by a restriction on aerosol emissions by ships, which was imposed in 2020 by the International Maritime Organization to combat the effect of aerosol pollutants on human health. Aerosols are small particles that serve as cloud formation nuclei. Their most important effect is to increase the extent and brightness of clouds, which reflect sunlight and have a cooling effect on Earth. When aerosols – and thus clouds – are reduced, Earth is darker and absorbs more sunlight, thus enhancing global warming. Ships are the main aerosol source in the North Pacific and North Atlantic Oceans. We quantify the aerosol effect from the geographical distribution of sunlight reflected by Earth as measured by satellites, with the largest expected and observed effects in the North Pacific and North Atlantic Oceans. We find that aerosol cooling, and thus climate sensitivity, are understated in the best estimate of the United Nations Intergovernmental Panel on Climate Change (IPCC).Global warming caused by reduced ship aerosols will not go away as tropical climate moves into its cool La Niña phase. Therefore, we expect that global temperature will not fall much below +1.5°C level, instead oscillating near or above that level for the next few years, which will help confirm our interpretation of the sudden global warming. High sea surface temperatures and increasing ocean hotspots will continue, with harmful effects on coral reefs and other ocean life. The largest practical effect on humans today is increase of the frequency and severity of climate extremes. More powerful tropical storms, tornadoes, and thunderstorms, and thus more extreme floods, are driven by high sea surface temperature and a warmer atmosphere that holds more water vapor. Higher global temperature also increases the intensity of heat waves and – at the times and places of dry weather – high temperature increases drought intensity, including “flash droughts” that develop rapidly, even in regions with adequate average rainfall.Polar climate change has the greatest long-term effect on humanity, with impacts accelerated by the jump in global temperature. We find that polar ice melt and freshwater injection onto the North Atlantic Ocean exceed prior estimates and, because of accelerated global warming, the melt will increase. As a result, shutdown of the Atlantic Meridional Overturning Circulation (AMOC) is likely within the next 20-30 years, unless actions are taken to reduce global warming – in contradiction to conclusions of IPCC. If AMOC is allowed to shut down, it will lock in major problems including sea level rise of several meters – thus, we describe AMOC shutdown as the “point of no return.”We suggest that an alternative perspective – a complement to the IPCC approach – is needed to assess these issues and actions that are needed to avoid handing young people a dire situation that is out of their control. This alternative approach will make more use of ongoing observations to drive modeling and more use of paleoclimate to test modeling and test our understanding. As of today, the threats of AMOC shutdown and sea level rise are poorly understood, but better observations of polar ocean and ice changes in response to the present accelerated global warming have the potential to greatly improve our understanding.
Lemon, A., Keith, D. W., & Albers, S. C. (2024). Under a not so white sky: visual impacts of stratospheric aerosol injection. Environmental Research Letters.Abstract: Stratospheric aerosol injection (SAI) could change the sky's appearance. This could play a role in shaping public perception of SAI. Noticeability depends strongly on tropospheric aerosol optical depth (AOD) and the amount of SAI used. We aim to quantify the noticeability of changes in sky color and brightness due to SAI. We use a 3D visible light radiative transfer package to generate cloudless sky images during high sun, sunset, and twilight under SAI from the reference point of a ground observer. We consider three aerosol types: H2SO4, CaCO3, and diamond. We consider stratospheric aerosol loadings required to produce radiative forcings of −1, −2, and −4 W m−2. We use population density and AOD data to compute the distribution of AODs people experience and then simulate sky images for the 10th, 50th, and 90th percentiles of that distribution. We compare the simulated changes in color and brightness to experimental measurements of minimum thresholds humans can detect. The three aerosol types cause similar changes, except most notably the diamond aerosol increases brightness of the solar aureole by roughly three to five times less than do H2SO4 or CaCO3. During high sun, sky whitening from sulfate SAI at −2 W m−2 is undetectable for roughly half of observers chosen randomly from the global population. For the remainder of the population, we expect whitening to still be unnoticeable for all but perhaps the most astute observers aided by color samples. Brightening and enlargement of the solar aureole is the most visible feature during high sun for H2SO4 and CaCO3, while changes near twilight would be the most noticeable impact of SAI. We cannot evaluate the fraction of the population who would notice these changes.
McLaren, D. (2024). “It's Not the Climate, Stupid”: Exploring Nonideal Scenarios for Solar Geoengineering Development. Ethics & International Affairs, 38(3), 255-274.Abstract: As part of the “Solar Geoengineering: Ethics, Governance, and International Politics” roundtable, this essay examines dilemmas arising in exploring nonideal scenarios of solar geoengineering deployment. Model-based knowledge about solar geoengineering tells us little about possible climatic responses to malicious, self-interested, or competing deployments, and even less about political or cultural responses outside of the climate system. The essay argues that policy for governing solar geoengineering in a world of multiple states and uneven power relations requires a broader base for solar geoengineering knowledge, beyond that offered by modeling, and a better understanding of nonideal scenarios, especially those motivated by logics beyond reducing climate impacts. It highlights the interests of military and security actors in such knowledge, and the potential for it to facilitate securitization and further reduce the prospect of multilateral collaborative governance of geoengineering in the public interest. The essay concludes that further research can be ethically justified but must be comprehensively governed.
Yan, X., Peng, S., Yang, M., Duan, W., & Cui, H. (2025). Carbonation of BaSO4 NPs Modified Alkali-Activated GGBS for Passive Daytime Radiative Cooling. ACS Sustainable Chemistry & Engineering.Abstract: In this study, alkali-activated granulated blast furnace slag (AAS) was selected as a low-carbon precursor for fabricating an inorganic radiative cooler via accelerated carbonation and BaSO4 nanoparticles (NPs) modification. The influence of the accelerated carbonation and BaSO4 dosages on the solar reflectance and thermal emittance were experimentally investigated, along with multiple analytical characterizations that provide insights into the correlation between phase/microstructure transformation and optical properties. Additionally, small-scale field tests were conducted to validate the cooling performance of the as-fabricated sample in outdoor environments. An energy balance analysis was subsequently performed to calculate the corresponding net cooling power. The results revealed that the synergy of carbonation and BaSO4 NPs significantly improved the solar reflectance from 10.3 to 83.9% while having negligible impact on the thermal emittance. Mechanism analysis indicated that the whitening effect of BaSO4 NPs and its capability to promote the formation of calcite and capillary pore were responsible for the improved solar reflectance. Outdoor measurements demonstrated an excellent passive cooling performance compared to the plain sample, with an average temperature drop of ∼10 °C in the midday, corresponding to a net cooling power of 59 W/m2. This work paves the way for upcycling waste slag into a high-performance passive cooling material while also capturing CO2 for energy-efficient buildings.
Määttänen, A., Ravetta, F., Lurton, T., & Boucher, O. (2025). Idealized modeling of stratospheric aerosol injection deployment scenarios with two uncooperative actors.Abstract: We have coupled multiple Proportional-Integral-Derivative (PID) controllers to a simple climate model to investigate solar radiation management scenarios using stratospheric aerosol injection (SAI). The climate model describes the evolution of hemispheric temperatures and an Indian monsoon index in response to annual SAI at a range of locations. The stratospheric aerosol optical depth evolution after sulfur injections and the monsoon response are parameterized based on simulations with a global climate model. The controller models the behavior of an actor that deploys SAI to reach a certain climatic goal, such as an average temperature or a monsoon precipitation target. We have implemented different deployment scenarios with two actors. Continuous deployment by two actors that do not cooperate sometimes leads to the actors not fully reaching their targets. An experiment where one of the actors stops for a while and then resumes SAI leads to a free-riding situation with one actor doing most of the work. Intermittent SAI experiments, where actors halt deployment for a period due to perceived failure or decision-makers changing their minds, bring about oscillations of hemispheric and global mean temperatures, and the targets are missed. These results emphasize the need for global SRM governance. More complex experiments, including multi-target controllers and coalitions of actors, will be possible with a future version of the model.
Eastham, S. D., Butler, A. H., Doherty, S. J., Gasparini, B., Tilmes, S., Bednarz, E. M., ... & Yu21, P. (2025). Addressing Gaps in Scientific Knowledge Could Improve Accuracy of Climate Intervention Assessments.Abstract: Solar radiation modification (SRM) is increasingly discussed as a potential method to ameliorate some negative effects of climate change. However, unquantified uncertainties in the physical and environmental impacts of SRM impede informed debate and decision making. Some uncertainties are due to a lack of understanding of processes determining the atmospheric effects of SRM and/or a lag in development of their representation in models, meaning that even high-quality model intercomparisons will not necessarily reveal or address them. Although climate models at multiple scales are advancing in complexity, there are specific areas of uncertainty where additional model development – often requiring new observational data - could significantly advance our understanding of SRM’s likely effects, and therefore improve our ability to assess and weigh its potential risks against those of choosing to not use SRM. We convene expert panels in the areas of atmospheric science most critical to understanding the three most widely-discussed forms of SRM. Each identifies three key modeling gap relevant to either stratospheric aerosols, cirrus clouds, or low-altitude marine clouds. In addition to arguing for more observations, the panels argue that model development work to either leverage different capabilities of existing models, bridge the scales across which relevant processes operate, or address specific, known modeling gaps could yield benefits in understanding. By focusing effort on addressing these knowledge gaps, we believe that themodeling community could advance our understanding of SRM’s physical risks as well as its potential benefits, allowing better-informed decision-making about whether and how to use SRM.
WEB POSTS
REPORTS
RESOURCE
UPCOMING EVENTSSolar Geoengineering Events Calendar
PODCASTSSky whitening - Lemon | Reviewer 2 does geoengineering | Sky whitening - Lemon Reviewer 2 does geoengineering 1:13:09 |
"Would a whiter sky be noticeable, under SAI geoengineering? Ansar Lemon discusses what humans and animals could see. Paper: Under a not so white sky: visual impacts of stratospheric aerosol injection - Ansar Lemon et al 2025 Environ. Res. Lett. 20 024060 DOI 10.1088/1748-9326/ada2ae A link to his music is here"
The Geopolitics of SRM | Climate Reflections: The SRM360 Podcast | The Geopolitics of SRM Climate Reflections: The SRM360 Podcast 18:36 |
"Climate change will disrupt the geopolitical landscape. So will Sunlight Reflection Methods (SRM). But might SRM help reduce international tensions by reducing the impacts of climate change? Or will these methods cause more or worse disruptions? For this episode of Climate Reflections, host Pete Irvine speaks with geopolitical experts to explore the current geopolitical landscape and how SRM might interact with it to impact international relations."
We have to talk about solar geoengineering, part 1 with Kelly Wasner | Wicked Problems Wicked ProblemsI’m not sleeping too well at the moment. My current wine/blood/caffeine ratio is not sustainable. Yeats’ over-quoted “Second Coming” feels like a cheery pep talk. The “Doomsday Clock” of the Bulletin of Atomic Scientists has been set at 89 seconds to midnight. But I was raised to believe despair is a sin, so while I’m going to just do what it takes to get through this week, and the next one, and the next one, I also reserve the right to just take a moment to appreciate the absurdity of this horror show… 6 days ago · 1 like · Richard Delevan and Kelly Wanser Degrees Initiative, Centering the Global South - interview with Andy Parker | Wicked ProblemsWicked Problems It’s the best of times, it’s the worst of times. I don't know about you, but the whipsaw between good news, bad news and really, really dire news is…a lot. And it’s not going to get any better any time soon… 3 hours ago · 1 like · Richard Delevan
YOUTUBE VIDEOSSAM webinar - Solar Radiation Modification: What’s at stake for society? | Academia Europaea Cardiff Knowledge Hub "Solar Radiation Modification (SRM) covers a range of technologies that have the potential to cool the Earth’s climate. SRM is therefore the subject of intense and controversial debate around whether it might provide a means to tackle global warming and the devastating impacts of climate change."
Global Warming Has Accelerated: An Intimate Conversation with Leading Climate Scientists | SDSN "An engaging discussion on groundbreaking research that reveals the unexpected drivers behind the recent unprecedented rise in global temperatures. Moderated by SDSN President Professor Jeffrey Sachs, this virtual event explored Dr. James Hansen and colleagues' findings in the latest publication, “Global Warming Has Accelerated,” their implications for climate sensitivity, and the urgent need for alternative approaches to mitigate the looming "point of no return."
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