Solar Geoengineering Weekly Summary (24 February - 02 March 2025)

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Mar 3, 2025, 2:37:32 PM3/3/25
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Here’s is your weekly roundup of SRM updates from the past week (24 February - 02 March 2025):

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1. Research Papers
2. Web Posts
3. SRM Books
4. YouTube Videos
5. Upcoming Events

The Big Green Button: Stratospheric Aerosol Injection as a Geopolitical Dilemma During Strategic Competition Between the United States and China, and Implications for Expanding Aerosol Injection Near-term Research

Nielsen, J. (2025). The Big Green Button: Stratospheric Aerosol Injection as a Geopolitical Dilemma During Strategic Competition Between the United States and China, and Implications for Expanding Aerosol Injection Near-term Research. Oxford Open Climate Change, kgaf009.
Abstract: This research examines SAI policy options through a dyadic international relations framework between the United States and China. Deploying large-scale SAI to manage solar radiation presents states with a novel source of geopolitical influence through influencing global climate systems. While multiple political bodies like the United Nations, European Union, United States, China, and India could feasibly deploy SAI without full global consent, the United States and China are powerful enough to deploy large-scale SAI unilaterally. The United States and China currently perceive themselves as locked in “great power competition” with each other which exposes a mutual SAI national security gap and accompanying policy dilemma. Given their divergent global power strategies but mutual global climate interests, this research assesses how the United States and China could compete or cooperate on SAI strategies. This research’s dyadic analysis of four policy scenarios provides three conclusions. First, the United States and China could each benefit from SAI cooperation whether they are cooperating to deter or deploy SAI. Second, SAI cooperation presents a potential political off-ramp from great power competition that aligns with each state’s mutual climate security interests. Third, expanding SAI research and conventional mitigation could support near-term United States and China policymaking regardless of whether they ultimately pursue SAI deployment or deterrence strategies. SAI advocates and critics alike can use these scenarios and conclusions to better discuss SAI as a geopolitical security dilemma.

The effectiveness of solar radiation management using fine sea spray across multiple climatic regions

Song, Z., Yu, S., Li, P., Yao, N., Chen, L., Sun, Y., ... & Rosenfeld, D. (2025). The effectiveness of solar radiation management using fine sea spray across multiple climatic regions. Atmospheric Chemistry and Physics, 25(4), 2473-2494.
Abstract: MCB geoengineering aims to inject aerosols over oceans to brighten clouds and reflect more sunlight in order to offset the impacts of global warming or to achieve localized climate cooling. The relative contributions of direct and indirect effects in MCB implementations remain uncertain. Here, we quantify both effects by designing model simulations to simulate MCB for five open-ocean regions around the globe. Our results show that a uniform injection strategy that does not depend on wind speed captured the sensitive areas of the regions that produced the largest radiative perturbations during the implementation of MCB. When the injection amounts are low, the sea salt aerosol effect on shortwave radiation is dominated by the indirect effect via brightening clouds, showing obvious spatial heterogeneity. As the indirect effect of aerosols saturates with increasing injection rates, the direct effect increases linearly and exceeds the indirect effects, producing a consistent increase in the spatial distributions of top-of-atmosphere upward shortwave radiation. This study provides quantifiable radiation and cloud variability data for multiple regional MCB implementations and suggests that injection strategies can be optimized by adjusting injection amounts and selecting areas sensitive to injections.

Design and Simulation of a Logistically Constrained High-Latitude, Low-Altitude Stratospheric Aerosol Injection Scenario in the Energy Exascale Earth System Model (E3SM)

Wheeler, L., Wagman, B., Smith, W., Davies, P., Cook, B., Brunell, S., ... & Zeitler, T. (2025). Design and Simulation of a Logistically Constrained High-Latitude, Low-Altitude Stratospheric Aerosol Injection Scenario in the Energy Exascale Earth System Model (E3SM). Environmental Research Letters.
Abstract: The Arctic is warming faster than the rest of the globe, posing risks to climate tipping elements such as the collapse of the Greenland Ice Sheet, winter Arctic sea ice loss, weakening of the Atlantic Meridional Overturning Circulation, and permafrost collapse. SAI has shown potential to ameliorate these effects by reducing surface temperatures. Due to the potential for an asymmetric hemispheric response in precipitation, Arctic-only SAI is not recommended. Given the challenges associated with an Antarctic SAI program, including the lack of nearby large airports, however, we designed and simulated an Arctic-only logistically constrained SAI scenario, considering limitations imposed by factors affecting the planning, execution, and management of operations. Our scenario is constrained by aircraft development and delivery timelines. SAI deployment begins in 2032 and increases to a maximum annual injection of 6.7 TgSO2 by 2053 through 2070. The scenario is simulated in a modified version of the Energy Exascale Earth System Model (E3SMv2). Results indicate that Arctic-only SAI can reduce Northern Hemisphere temperatures and slow sea ice loss, though the early years of deployment may show limited cooling due to low ramp-in injection magnitudes. The Arctic-only SAI introduces minimal impact on Southern Hemisphere temperatures but significant shifts in the hydrologic cycle, particularly around the equator. Southern Hemisphere changes are low within the first two decades, suggesting that asymmetries in Arctic-only SAI deployment could be sustained without severe adverse climate impacts for the first couple of decades. These asymmetries matter given the challenges associated with an Antarctic SAI program. Our findings underscore the necessity of incorporating logistical constraints on deployment and the need for multi-model assessments in the evaluation of polar SAI scenarios. This approach would ensure a strong scientific understanding of polar SAI and facilitates policy and decision-maker understanding of the risks and benefits of SAI.

Feedback Trends with ECS from Energy Rates: Feedback Doubling and the Vital Need for Solar Geoengineering

Feinberg, A. (2025). Feedback Trends with ECS from Energy Rates: Feedback Doubling and the Vital Need for Solar Geoengineering. Climate, 13(3), 43.
Abstract: This paper provides climate feedback trends, quantifies the feedback-doubling (FD) period, considers urbanization influences, and provides related equilibrium climate sensitivity (ECS) estimates using data from 1880 to 2024. Data modeling is accomplished by focusing on statistically significant stable normalized correlated rates (NCRs, i.e., normalized related slopes). Estimates indicate that the global warming NCR is increasing by a factor of 1.65 to 2.33 times faster than the energy consumption NCR, from 1975 to 2024. The reason is feedback amplification. This is supported by the fact that the NCR for forcing and energy consumption shows approximate equivalency in the period studied. Results provide feedback yearly trend estimates at the 95% confidence level that key results will fall within the IPCC AR6 likely range. The projected 2017–2024 feedback amplification estimates, using the EC approach, range from 2.0 to 2.16, respectively. A feedback amplification of 2.0 (approximately equal to −2.74 Wm−2 K−1) doubles the forcing, indicating that in 2024, more than half of global warming (53.7%) is likely due to feedback. Relative to the feedback-doubling (FD) threshold (i.e., the point where feedback exceeds forcing), the FD overage is 3.7% in 2024. This is the amount of feedback exceeding the forcing portion found to have a surprisingly aggressive 3.1% to 3.9% estimated overage growth rate per decade. We now ask, shouldn’t we try to mitigate feedback as well as GHG forcing, and if forcing could be removed, would global warming fully “self-mitigate”? Additionally, CO2 yearly increases are complex, with poor reduction progress. Therefore, this study’s risk assessment urgently recommends that supplementary “mild” annual solar geoengineering is necessary, to reduce the dominant aggressive feedback. SG reduces the primary solar warming source creating 62% higher mitigation efficiency than CDR. Urgency is enhanced since solar geoengineering must be timely and can take years to develop. This study also estimates that 75% to 90.5% (83% average) of the feedback problem is due to water vapor feedback (WVF). High WVF also plagues many cities needing local SG. Trend analysis indicates that by 2047, the earliest we may reach 10 billion people, feedback amplification could reach a value of 2.4 to 2.8. Furthermore, by 2082, the year estimated for 2× CO2, at the current rate, feedback amplification could range from 2.88 to 3.71. This yields an ECS range from 2.4 °C to 3.07 °C, in reasonable agreement with the reported estimated range in AR6. An overview of recent urbanization forcing attribution indicates the ECS value may be lower by 10.7% if this forcing is considered. For numerous reasons, the lack of albedo urbanization Earth brightening requirements in the Paris Agreement, is unsettling. In addition, a model assesses effective forced feedback (EFF) temperature characteristics of up to 1.9 °C, providing interesting feedback insights that may relate to high GW land and pipeline temperature estimates. Lastly in addition to urbanization, solar geoengineering in the Arctic and Antarctic is advised. Worldwide efforts in GHG mitigation, with no significant work in SG, appears highly misdirected.

Simulated Terrestrial Climate and Carbon Cycle Response to Cloud Albedo Enhancement Over Ocean and Land - Preprint

Fang, Y., & Cao, L. Simulated Terrestrial Climate and Carbon Cycle Response to Cloud Albedo Enhancement Over Ocean and Land. Available at SSRN 5147439.
Abstract: Marine cloud brightening (MCB) has been proposed as a backup method to mitigate some impacts of global warming. Cloud albedo can be increased over ocean or land either intentionally or unintentionally. Our understanding of how the climate response differs between cloud albedo enhancement over ocean and land remains limited. In this study, we use the Community Earth System Model (CESM) to explore the impact of cloud albedo enhancement over either ocean or land on the terrestrial climate and carbon cycle. In our simulation design, both MCB and land cloud brightening (LCB) are applied over the latitude bands of 30ºS-30ºN under atmospheric CO2 concentration of 800 ppm to achieve a net negative radiative forcing of about -1 W m-2. Over large parts of the low latitude land, MCB increases precipitation by enhancing upward atmospheric motion, resulting in increased soil moisture. In contrast, LCB decreases precipitation by inducing subsidence, resulting in decreased soil moisture. Changes in climatic factors affect land gross primary productivity (GPP). Relative to the high CO2 world, LCB reduces GPP by 3.80 ± 0.09 GtC yr-1, which is about three times the reduction caused by MCB (1.34 ± 0.10 GtC yr-1). These differences in GPP responses are closely linked to changes in the hydrological cycle. In large parts of low-latitude regions, MCB increases soil moisture, which acts to enhance GPP. Conversely, LCB reduces soil moisture, which acts to suppress GPP. MCB and LCB-induced changes in temperature, sunlight, and vapor pressure deficit also play important roles in regulating GPP change. This study would help us to better understand terrestrial climate and carbon cycle consequences resulting from large-scale cloud albedo change over either ocean or land, as well as large scale albedo change over ocean and land surface.
Politics of Climate Tech: Billions spent on geo-engineering despite objections (Just the News)
Solar Geoengineering, Sovereignty, and the Case for Ecological Realism (SRM360)
Scientific advice on Solar Radiation Modification: An interview with Naki Nakićenović and Benjamin Sovacool (Academia Europaea)
No one is coming to save us. Time to cowboy up! (Keep Cool)
Solar Geoengineering: Risks and Geopolitical Challenges (Revista Cenarium)
International Law and Marine Geoengineering (by Robert C. Steenkamp)
Dimming the Sun: The Urgent Case for Solar Geoengineering (by Thomas Ramge)

Offstage: Debating Climate Interventions | Arctic Frontiers

"Geoengineering and large-scale climate interventions are controversial but increasingly discussed as the Arctic bears the brunt of climate change. This session examines the scientific, ethical, and governance dimensions of geoengineering and explores whether such solutions can complement existing climate strategies."

Columbia Climate School’s Signature Speaker Series featuring Elizabeth Kolbert | Columbia Climate School

"In this video, Elizabeth Kolbert discusses new paper: Under a White Sky: Solar Geoengineering and other bright ideas"

Later is too late, we urgently need research on sunlight reflection | Dakota Gruener | TEDx Talks

"Imagine something that could slow down global warming, potentially saving ecosystems, and protecting millions of lives from climate-induced disasters— yet we hesitate to even study it. Why? Because it's controversial. Sunlight reflection, or SRM, has been painted as dangerous, unnatural, and even unethical. But what if not exploring it is the real ethical issue? Dakota Gruener is the CEO of Reflective, a philanthropically funded organization working to accelerate responsible sunlight reflection research. Before this, Dakota built and led ID2020, the world’s leading standards-setting organization for privacy-protecting and user-managed digital ID."

Stratospheric Aerosol Injection Solid Particles for Climate Mitigation | Remove and Reflect Podcast

"In this episode, Mr. Sun (AI character) & Ms. Remove (AI character) discuss a new study that investigates the potential of injecting solid alumina and calcite particles into the stratosphere as an alternative to sulfur dioxide for mitigating global warming. The researchers used a climate model to compare the effects of these materials on stratospheric warming, ozone depletion, and diffuse radiation. The results suggest that solid particles could reduce stratospheric warming and diffuse radiation compared to sulfur dioxide. However, the study emphasizes that considerable uncertainties remain, particularly regarding the impact of these particles on stratospheric ozone due to poorly understood chemical processes. The research underscores the need for further laboratory studies to better understand the behavior of these materials in the stratosphere and to refine climate models. Ultimately, this work contributes to a more comprehensive assessment of the risks and benefits of solar geoengineering approaches.
Paper: Vattioni, S., Peter, T., Weber, R. et al. Injecting solid particles into the stratosphere could mitigate global warming but currently entails great uncertainties. Commun Earth Environ 6, 132 (2025). DOI.org/10.1038/s43247-025-02038-1
Note: This audio is entirely AI-generated"

Feedback Trends with ECS from Energy Rates: Feedback Doubling & Vital Need for Solar Geoengineering | Remove and Reflect Podcast

"In this podcast episode, Mr. Sun (AI character) & Ms. Remove (AI character) discuss a new paper that explores the growing role of feedback loops in global warming, showing that in 2024, feedback-driven warming (54%) has surpassed direct forcing (46%). While reducing greenhouse gas (GHG) emissions remains important, the study argues that feedback effects—mainly from water vapor—are accelerating too rapidly for emission cuts alone to be effective. Instead, it highlights solar geoengineering (SG) as a faster, more efficient approach to stabilizing temperatures.
The paper suggests strategies like brightening surfaces and reflecting sunlight in the stratosphere, emphasizing the urgent need for global collaboration. With no strong SG efforts currently in place, the study calls for space agencies like NASA and SpaceX to take action.
Paper: Feinberg, A. (2025). Feedback Trends with ECS from Energy Rates: Feedback Doubling and the Vital Need for Solar Geoengineering. Climate, 13(3), 43.
Note: This audio is entirely AI-generated"
Solar radiation modification: What are the technologies, and what are the risks? by Scientific Advice Mechanism to the European Commission | 11 March 2025 | Online
International Conference on Arctic Research Planning IV Summit and Arctic Science Summit Week IASC | 20-28 March 2025 | Boulder, Colorado, USA
Climate Intervention: Distraction or Necessity? by Center for Climate Repair | 21 March 2025
2025 Solar Radiation Management Annual Meeting by Simons Foundation | 24-25 April 2025 | New York
The 2025 Degrees Global Forum | 12-16 May 2025 | Cape Town, South Africa
Consultative Workshop and Science-Policy Dialogue on Solar Radiation Modification by UNEP | 19-20 May 2025 | Switzerland
Artic Repair Conference 2025 by University of Cambridge & Center for Climate Repair | 26-28 June 2025 | Cambridge UK

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