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Abstract Sea level rise (SLR) is a global concern in the era of climate change, prompting the exploration of interventions such as solar radiation modification through stratospheric aerosol injection (SAI). This intervention could affect the physical system in various ways. The present study analyzes the global and regional impacts of SAI using ARISE-SAI-1.5 (SAI-1.5) simulations with the Community Earth System Model 2. We calculated the regional thermosteric sea level under different scenarios. After validating our methodology for sea level components over the period 1995–2014, we determined changes in sea level variables under both SAI-1.5 and the underlying Shared Socioeconomic Pathway 2–4.5 (SSP2-4.5) relative to the reference period (1995–2014). In contrast to sea surface temperature, which under this SAI strategy should be maintained near 1.5 °C above preindustrial values, global SLR would continue increasing under SAI-1.5. However, SAI would significantly impact thermal expansion in SSP2-4.5 simulations, reducing the global long-term sea level trend from 3.7 ± 0.03 mm yr⁻¹for SSP2-4.5–1.9 ± 0.04 mm yr⁻¹for SAI-1.5, a 49% reduction. The associated ocean heat content is reduced from (2.0 ± 0.3) × 10²²J yr⁻¹under SSP2-4.5 to (1.17 ± 0.30) × 10²²J yr⁻¹under SAI, a 42% reduction. Additionally, SAI would impact the regional and global ocean by reducing the SLR rate. These findings underscore the potential of SAI as a climate intervention strategy with significant implications for sea level change. 

Abstract Solar radiation modification (SRM) is a climate intervention method that would reflect a portion of incoming solar radiation to cool the Earth and could be used to ameliorate the impacts of climate change, but that provokes strong reactions from experts and the public alike. Research has explored both the biophysical and human behavioral aspects of SRM but has not integrated these processes in a single framework. Our expectations for SRM development and deployment will be inaccurate until we integrate the feedbacks between human behavioral and cognitive processes and the biophysical and climate system. We propose a framework for describing these feedbacks and how they may mediate transitions in the development and operationalization of SRM as a climate intervention. We consider components such as public trust in SRM, moral hazard concerns, climate risk perceptions, and societal disruptions, and illustrate how the driving processes could change across the pre-development, post-development, and post-deployment phases of SRM operationalization to affect outcomes around SRM deployment and climate change. Our framework illustrates the importance of feedbacks between climate change, risk perceptions, and the human response and the necessity to integrate such feedbacks in the development of future scenarios for SRM. 

The Geoengineering Model Intercomparison Project (GeoMIP) held its 14th annual workshop, with almost 70 in-person participants and 15 remote participants for a robust discussion about future experiments and community needs in light of phase 7 of the Coupled Model Intercomparison Project (CMIP7). 

ABSTRACT Methane emissions by global wetlands are anticipated to increase due to climate warming. The increase in methane represents a sizable emissions source (32–68 Tg CH₄year⁻¹greater in 2099 than 2010, for RCP2.6–4.5) that threatens long‐term climate stability and poses a significant positive feedback that magnifies climate warming. However, management of this feedback, which is ultimately driven by human‐caused warming and thus “indirectly” anthropogenic, has been largely unexplored. Here, we review the known range of options for direct management of rising wetland methane emissions, outline contexts for their application, and explore a global scale thought experiment to gauge their potential impact. Among potential management options for methane emissions from wetlands, substrate amendments, particularly sulfate, are the most well studied, although the majority have only been tested in laboratory settings and without considering potential environmental externalities. Using published models, we find that the bulk (64%–80%) of additional wetland methane will arise from hotspots making up only about 8% of global wetland extent, primarily occurring in the tropics and subtropics. If applied to these hotspots, sulfate might suppress 10%–21% of the total additional wetland methane emissions, but this treatment comes with considerable negative consequences for the environment. This thought experiment leverages results from experimental simulations of sulfate from acid rain, as there is essentially no research on the use of sulfate for intentional suppression of additional wetland methane emissions. Given the magnitude of the potential climate forcing feedback of methane from wetlands, it is critical to explore management options and their impacts to ensure that decisions made to directly manage—or not manage—this process be made with the best available science. 

Abstract Stratospheric aerosol injection (SAI) would involve the addition of sulfate aerosols in the stratosphere to reflect part of the incoming solar radiation, thereby cooling the climate. Studies trying to explore the impacts of SAI have often focused on idealized scenarios without explicitly introducing what we call ‘inconsistencies’ in a deployment. A concern often discussed is what would happen to the climate system after an abrupt termination of its deployment, whether inadvertent or deliberate. However, there is a much wider range of plausible inconsistencies in deployment than termination that should be evaluated to better understand associated risks. In this work, we simulate a few representative inconsistencies in a pre-existing SAI scenario: an abrupt termination, a decade-long gradual phase-out, and 1 year and 2 year temporary interruptions of deployment. After examining their climate impacts, we use these simulations to train an emulator, and use this to project global mean temperature response for a broader set of inconsistencies in deployment. Our work highlights the capacity of a finite set of explicitly simulated scenarios that include inconsistencies to inform an emulator that is capable of expanding the space of scenarios that one might want to explore far more quickly and efficiently. 

Abstract Climate change is a prevalent threat, and it is unlikely that current mitigation efforts will be enough to avoid unwanted impacts. One potential option to reduce climate change impacts is the use of stratospheric aerosol injection (SAI). Even if SAI is ultimately deployed, it might be initiated only after some temperature target is exceeded. The consequences of such a delay are assessed herein. This study compares two cases, with the same target global mean temperature of ∼1.5° C above preindustrial, but start dates of 2035 or a ‘delayed’ start in 2045. We make use of simulations in the Community Earth System Model version 2 with the Whole Atmosphere Coupled Chemistry Model version 6 (CESM2-WACCM6), using SAI under the SSP2-4.5 emissions pathway. We find that delaying the start of deployment (relative to the target temperature) necessitates lower net radiative forcing (−30%) and thus larger sulfur dioxide injection rates (+20%), even after surface temperatures converge, to compensate for the extra energy absorbed by the Earth system. Southern hemisphere ozone is higher from 2035 to 2050 in the delayed start scenario, but converges to the same value later in the century. However, many of the surface climate differences between the 2035 and 2045 start simulations appear to be small during the 10–25 years following the delayed SAI start, although longer simulations would be needed to assess any longer-term impacts in this model. In addition, irreversibilities and tipping points that might be triggered during the period of increased warming may not be adequately represented in the model but could change this conclusion in the real world.