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Jun 3, 2024, 4:28:17 PMJun 3
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Stratospheric transport and tropospheric sink of solar geoengineering aerosol: a Lagrangian analysis

Sun, H., Bourguet, S., Luan, L., & Keith, D. (2024). Stratospheric transport and tropospheric sink of solar geoengineering aerosol: a Lagrangian analysis. npj Climate and Atmospheric Science, 7(1), 115.


Stratospheric aerosol injection (SAI) aims to reflect solar radiation by increasing the stratospheric aerosol burden. To understand how the background circulation influences stratospheric transport of injected particles, we use a Lagrangian trajectory model (lacking numerical diffusion) to quantify particles’ number, flux, lifetime, and tropospheric sinks from a SAI injection strategy under present-day conditions. While particles are being injected, stratospheric particle number increases until reaching a steady-state. During the steady-state, the time series of particle number shows a dominant period of ~2 years (rather than a 1-year cycle), suggesting modulation by the quasi-biannual oscillation. More than half of particles, injected in the tropical lower stratosphere (15° S to 15° N, 65 hPa), undergo quasi-horizontal transport to the midlatitude. We find a zonal asymmetry of particles’ tropospheric sinks that are co-located with tropopause folding beneath the midlatitude jet stream, which can help predict tropospheric impacts of SAI (e.g., cirrus cloud thinning).

Abrupt reduction in shipping emission as an inadvertent geoengineering termination shock produces substantial radiative warming

Yuan, T., Song, H., Oreopoulos, L., Wood, R., Bian, H., Breen, K., ... & Platnick, S. (2024). Abrupt reduction in shipping emission as an inadvertent geoengineering termination shock produces substantial radiative warming. Communications Earth & Environment, 5(1), 281.


Human activities affect the Earth’s climate through modifying the composition of the atmosphere, which then creates radiative forcing that drives climate change. The warming effect of anthropogenic greenhouse gases has been partially balanced by the cooling effect of anthropogenic aerosols. In 2020, fuel regulations abruptly reduced the emission of sulfur dioxide from international shipping by about 80% and created an inadvertent geoengineering termination shock with global impact. Here we estimate the regulation leads to a radiative forcing of Wm−2 averaged over the global ocean. The amount of radiative forcing could lead to a doubling (or more) of the warming rate in the 2020 s compared with the rate since 1980 with strong spatiotemporal heterogeneity. The warming effect is consistent with the recent observed strong warming in 2023 and expected to make the 2020 s anomalously warm. The forcing is equivalent in magnitude to 80% of the measured increase in planetary heat uptake since 2020. The radiative forcing also has strong hemispheric contrast, which has important implications for precipitation pattern changes. Our result suggests marine cloud brightening may be a viable geoengineering method in temporarily cooling the climate that has its unique challenges due to inherent spatiotemporal heterogeneity.

Response of the Southern Hemisphere extratropical cyclone climatology to climate intervention with stratospheric aerosol injection

Reboita, M. S., Gabriel Martins Ribeiro, J., Machado Crespo, N., da Rocha, R. P., Odoulami, R. C., Sawadogo, W., & Moore, J. C. (2024). Response of the Southern Hemisphere extratropical cyclone climatology to climate intervention with stratospheric aerosol injection. Environmental Research: Climate.


Little is known about how climate intervention through stratospheric aerosol injection (SAI) may affect the climatology of the Southern Hemisphere extratropical cyclones under warming scenarios. To address this knowledge gap, we tracked extratropical cyclones from 2015 to 2099 in a set of projections of three international projects: the Assessing Responses and Impacts of Solar Climate Intervention on the Earth System with Stratospheric Aerosol Injection (ARISE), the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS), and the Geoengineering Model Intercomparison Project (GeoMIP/G6sulfur). Comparisons were performed between no-SAI and SAI scenarios as well as between different timeslices and their reference period (2015-2024). Among the findings, both no-SAI and SAI project a decrease in cyclone frequency towards the end of the century although weaker under SAI scenarios. On the other hand, cyclones tend to be stronger under no-SAI scenarios while keeping their intensity more similar to the reference period under SAI scenarios. This means that under SAI scenarios the climatology of cyclones is less affected by global warming than under no-SAI. Other features of these systems, such as travelling distance, lifetime, and mean velocity show small differences between no-SAI and SAI scenarios and between reference and future periods.

Toward an evidence-informed, responsible, and inclusive debate on solar geoengineering: A response to the proposed non-use agreement

Parson, E. A., Buck, H. J., Jinnah, S., Moreno‐Cruz, J., & Nicholson, S. (2024). Toward an evidence‐informed, responsible, and inclusive debate on solar geoengineering: A response to the proposed non‐use agreement. Wiley Interdisciplinary Reviews: Climate Change, e903.


A prominent recent perspective article in this journal and accompanying open letter propose a broad international “non-use agreement” (NUA) on activities related to solar geoengineering (SG). The NUA calls on governments to renounce large-scale use of SG, and also to refuse to fund SG research, ban outdoor experiments, decline to grant IP rights, and reject discussions of SG in international organizations. We argue that such pre-emptive rejection of public research and consultation would deprive future policy-makers of knowledge and capability that would support informed decisions to safely and equitably limit climate risk, sustain human welfare, and protect threatened ecosystems. In contrast to the broad prohibitions of the NUA, we propose an alternative near-term pathway with five elements: assess SG risks and benefits in the context of related climate risks and responses; distinguish the risks and governance needs of SG research and deployment; pursue research that treats uncertainties and divergent results even-handedly; harness normalization of SG as a path to effective assessment and governance; and build a more globally inclusive conversation on SG and its governance. These principles would support a more informed, responsible, and inclusive approach to limiting climate risks, including judgments on the potential role or rejection of SG, than the prohibitory approach of the NUA.

Chinese public’s perceptions and understanding of the potential roles of solar climate engineering for reducing climate change risks

Zhang, Z., Huisingh, D., & Crabbe, M. J. C. (2024). Chinese public’s perceptions and understanding of the potential roles of solar climate engineering for reducing climate change risks. Environment, Development and Sustainability, 1-20.


Limiting global temperature increases appear to be an exceedingly challenging task due to great difficulty in advancing carbon reduction emission negotiation. Solar climate engineering is emerging as an emergency shield for climate risks. Except for its technical feasibility and reasonable costs, public understanding is essential for future implementation. Compared with wide studies in Europe and North America, our study was the first large-scale survey to comprehensively investigate the Chinese public’s attitude toward solar climate engineering. Moreover, our study was the first to focus on combined solar climate engineering schemes and investigate Public attitude toward international governance and regulatory structures. Our survey revealed that: The surveyed Chinese participants perceived a high level of its deployment costs and a middle level of its effectiveness, technical readiness and side effects. A majority of surveyed participants supported China’s active role in international governance and regulatory structures for solar climate engineering. About a half of the surveyed participants were willing to pay taxes to support related research and possible future deployment. However, when solar climate engineering was compared with seven mainstream climate change mitigation schemes, Chinese participants favored less priority and less funding for solar climate engineering. This means that Chinese participants viewed it as only a backup option in climate strategies.

Africa's Climate Response to Marine Cloud Brightening

Odoulami, R. C., Hirasawa, H., Kouadio, K., Patel, T. D., Quagraine, K. A., Pinto, I., ... & New, M. G. (2024). Africa's Climate Response to Marine Cloud Brightening (No. EGU24-6419). Copernicus Meetings.


Climate intervention through solar radiation modification is one proposed method for reducing climate risks from anthropogenic warming. Marine Cloud Brightening (MCB), one such approach, proposes to inject sea salt aerosol into a regional marine boundary layer to increase marine clouds' reflectivity. This study assessed the potential influence of four MCB experiments on the climate in Africa using simulations from the Community Earth System Model (CESM2) with the Community Atmospheric Model (CAM6). Four idealised MCB experiments were performed with the CESM2(CAM6) model under a medium-range background forcing scenario (SSP2-4.5) by setting cloud droplet number concentrations to 600 cm-3 over three subtropical ocean regions: (a) Northeast Pacific (MCBNEP); (b) Southeast Pacific (MCBSEP); (c) Southeast Atlantic (MCBSEA); and (d) the combination of these three regions (MCBALL). The CESM2(CAM6) model reproduces the observed spatial distribution and seasonal cycle of precipitation and minimum and maximum temperatures over Africa and its climatic zones well. The results suggest that MCBSEP would induce the strongest global cooling effect and thus could be the most effective in decreasing (increasing) temperatures (precipitation) and associated extremes across most parts of the continent, especially over West Africa, in the future (2035-2054) while other regions could remain warmer or dryer compared to the historical climate (1995-2014). While the projected changes under MCBALL are similar to those of MCBSEP, MCBNEP and MCBSEA could result in more warming and, in some regions of Africa, create a warmer future than under SSP2-4.5. Also, all MCB experiments are more effective in cooling maximum temperature and related extremes than minimum temperature and related extremes. These findings further suggest that the climate impacts of MCB in Africa are highly sensitive to the deployment region.

A Living Assessment of Different Materials for Stratospheric Aerosol Injection—Building Bridges Between Model World and the Messiness of Reality

Visioni, D., Quaglia, I., & Steinke, I. (2024). A living assessment of different materials for stratospheric aerosol injection—Building bridges between model world and the messiness of reality. Geophysical Research Letters, 51(10), e2024GL108314.


There are obstacles in better understanding the climate impacts associated with new materials that could be used for Stratospheric Aerosol Injections (SAI), like the lack of an integrated framework that combines climate modeling across scales, laboratory studies and small-scale field experiments. Vattioni et al. (2023, explored one aspect of using alternative, non-sulfate materials for SAI. They investigated how uncertain the response of stratospheric ozone would be to alumina injections for SAI. In their study, they quantify chlorine activation rates in the presence of alumina, and then cascade these uncertainties into estimates of ozone depletion, concluding that alumina might have less detrimental impacts on stratospheric chemistry than sulfate, but with large uncertainties. Their results provide a useful basis upon which future research endeavors combining indoor and outdoor experiments and modeling may be structured to produce robust assessments of SAI impacts, benefits and uncertainties, together with clarifying what kind of research needs to be prioritized.


The Need for Geoengineering (HPAC)
Honest dialogue is needed to help build consensus around solar radiation modification technology (The Conversation)


Postdoc High-fidelity Computations of Aerosol Dynamics in Stratospheric Aircraft Wakes at TU Delft University of Technology

"In this postdoc position, you will form part of a consortium of researchers at ETH Zurich, the Paul Scherrer institute, the Physical Meteorological Observatory, the University of West Indies and ITS Indonesia with the goal of accurately quantifying the physics and effects of SAI. Your role will be to combine large-eddy simulations with particle evolution models to initially examine near-wake aerosol dynamics, then to study long-term aerosol wake evolution. This will provide input to predictions of large-scale aerosol properties which will be employed in global climate simulations. The results of these simulations will be used in case studies quantifying local impacts, with detailed studies to be performed for the West Indies and Indonesia. The anticipated outputs of this consortium are crucial for decision makers, who should have realistic assessments of the risks associated with SAI techniques before considering their incorporation into global warming management strategies."


re:publica 2024: Thomas Ramge - Solar Geoengineering – Why we must dim the sun before | re:publica

"Solar Geoengineering – Why we must dim the sun before entering the post-fossil age

Humanity is not decarbonizing decisively enough. In a few decades from now, we will likely live on a planet with 2 degrees of global warming. Without solar geoengineering, billions of people will suffer unbearable consequences. Reflecting sunlight into space will be our best option to gain time." 

Is this the cheapest Solar Radiation Modification method? | Neofizix

"Solar radiation modification is one of the prominent ideas considered for reducing global warming. Injecting aerosol particles into the atmosphere is thought to be the cheapest radiation modification approach. It costs about $18 billion/yr over 66 years to reduce the global mean temperature by 1 degree Celsius. We describe a method which could cost as low as $1.6 billion/yr to reduce the global mean temperature by 1 degree Celsius. Perhaps we can engineer a better Earth together using this approach."

NOAC meeting - 13th May 2024 | Clive Elsworth


•Greg – Gwyne Dyer’s book

John M – MCB study put on hold – Alameda

•Greg – how much SO2 is needed for SAI to cool Earth by 0.1C?

•Sev – Theses e.g.:- Mitigation – oil/gas good for future"

HPAC Meeting with Hans Van Der Loo and Wouter von Dieren 30 May 2024 | Robbie Tulip

"The Healthy Planet Action Coalition in conversation with two very special guests. Wouter van Dieren and Hans van der Loo are long time highly accomplished change-makers and climate advocates from the Netherlands. They cofounded the Blue Cooling Initiative,, an NGO committed to “buying time for survival of humanity by temporarily cooling the planet.” They are now actively engaged in establishing the International Climate Cooling Coalition, an NGO whose goal is to advance the need for DCC - Direct Climate Cooling - or Active Cooling as they call it."

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