*WEEKLY SUMMARY (18 SEPTEMBER - 24 SEPTEMBER 2023)* <https://www.scientificamerican.com/article/its-time-to-engineer-the-sky/> ------------------------------ RESEARCH PAPERSClimate, Variability, and Climate Sensitivity of “Middle Atmosphere” Chemistry Configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)) <https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022MS003579>
N. A. Davis, D. Visioni, R. R. Garcia, D. E. Kinnison, D. R. Marsh, M. Mills, J. H. Richter, S. Tilmes, C. G. Bardeen, A. Gettelman, A. A. Glanville, D. G. MacMartin, A. K. Smith, F. Vitt. Climate, Variability, and Climate Sensitivity of “Middle Atmosphere” Chemistry Configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)), Advancing Earth & Space Sciences, https://doi.org/10.1029/2022MS003579, 2021.AbstractSimulating whole atmosphere dynamics, chemistry, and physics is computationally expensive. It can require high vertical resolution throughout the middle and upper atmosphere, as well as a comprehensive chemistry and aerosol scheme coupled to radiation physics. An unintentional outcome of the development of one of the most sophisticated and hence computationally expensive model configurations is that it often excludes a broad community of users with limited computational resources. Here, we analyze two configurations of the Community Earth System Model Version 2, Whole Atmosphere Community Climate Model Version 6 (CESM2(WACCM6)) with simplified “middle atmosphere” chemistry at nominal 1 and 2° horizontal resolutions. Using observations, a reanalysis, and direct model comparisons, we find that these configurations generally reproduce the climate, variability, and climate sensitivity of the 1° nominal horizontal resolution configuration with comprehensive chemistry. While the background stratospheric aerosol optical depth is elevated in the middle atmosphere configurations as compared to the comprehensive chemistry configuration, it is comparable among all configurations during volcanic eruptions. For any purposes other than those needing an accurate representation of tropospheric organic chemistry and secondary organic aerosols, these simplified chemistry configurations deliver reliable simulations of the whole atmosphere that require 35% and 86% fewer computational resources at nominal 1 and 2° horizontal resolution, respectively. CO2-equivalence metrics for surface albedo change based on the radiative forcing concept: a critical review <https://doi.org/10.5194/acp-21-9887-2021> Ryan M. Bright and Marianne T. Lund, Atmos. Chem. Phys., 21, 9887–9907, https://doi.org/10.5194/acp-21-9887-2021, *2021*.*Abstract*Management of Earth's surface albedo is increasingly viewed as an important climate change mitigation strategy both on (Seneviratne et al., 2018) and off (Field et al., 2018; Kravitz et al., 2018) the land. Assessing the impact of a surface albedo change involves employing a measure like radiative forcing (RF) which can be challenging to digest for decision-makers who deal in the currency of CO2-equivalent emissions. As a result, many researchers express albedo change (Δ*α*) RFs in terms of their CO2-equivalent effects, despite the lack of a standard method for doing so, such as there is for emissions of well-mixed greenhouse gases (WMGHGs; e.g., IPCC AR5, Myhre et al., 2013). A major challenge for converting Δ*α* RFs into their CO 2-equivalent effects in a manner consistent with current IPCC emission metric approaches stems from the lack of a universal time dependency following the perturbation (perturbation “lifetime”). Here, we review existing methodologies based on the RF concept with the goal of highlighting the context(s) in which the resulting CO2-equivalent metrics may or may not have merit. To our knowledge this is the first review dedicated entirely to the topic since the first CO2-eq. metric for Δ*α* surfaced 20 years ago. We find that, although there are some methods that sufficiently address the time-dependency issue, none address or sufficiently account for the spatial disparity between the climate response to CO2 emissions and Δ*α* – a major critique of Δ*α* metrics based on the RF concept (Jones et al., 2013). We conclude that considerable research efforts are needed to build consensus surrounding the RF “efficacy” of various surface forcing types associated with Δ*α* (e.g., crop change, forest harvest), and the degree to which these are sensitive to the spatial pattern, extent, and magnitude of the underlying surface forcings. Overlooked Long-Term Atmospheric Chemical Feedbacks Alter the Impact of Solar Geoengineering: Implications for Tropospheric Oxidative Capacity <https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023AV000911> Jonathan M. Moch, Loretta J. Mickley, Sebastian D. Eastham, Elizabeth W. Lundgren, Viral Shah, Jonathan J. Buonocore, Jacky Y. S. Pang, Mehliyar Sadiq, Amos P. K. Tai. *Advancing Earth & Space Sciences*, https://doi.org/10.1029/2023AV000911, *2023.**Abstract*Studies of the impacts of solar geoengineering have mostly ignored tropospheric chemistry. By decreasing the sunlight reaching Earth's surface, geoengineering may help mitigate anthropogenic climate change, but changing sunlight also alters the rates of chemical reactions throughout the troposphere. Using the GEOS-Chem atmospheric chemistry model, we show that stratospheric aerosol injection (SAI) with sulfate, a frequently studied solar geoengineering method, can perturb tropospheric composition over a span of 10 years, increasing tropospheric oxidative capacity by 9% and reducing methane lifetime. SAI decreases the overall flux of shortwave radiation into the troposphere, but increases flux at certain UV wavelengths due to stratospheric ozone depletion. These radiative changes, in turn, perturb tropospheric photochemistry, driving chemical feedbacks that can substantially influence the seasonal and spatial patterns of radiative forcing beyond what is caused by enhanced stratospheric aerosol concentrations alone. For example, chemical feedbacks decrease the radiative effectiveness of geoengineering in northern high latitude summer by 20%. Atmospheric chemical feedbacks also imply the potential for net global public health benefits associated with stratospheric ozone depletion, as the decreases in mortality resulting from SAI-induced improvements in air quality outweigh the increases in mortality due to increased UV radiation exposure. Such chemical feedbacks also lead to improved plant growth. Our results show the importance of including fuller representations of atmospheric chemistry in studies of solar geoengineering and underscore the risk of surprises from this technology that could carry unexpected consequences for Earth's climate, the biosphere, and human health. Thermosteric and dynamic sea level under solar geoengineering <https://www.nature.com/articles/s41612-023-00466-4> Yue, C., Jevrejeva, S., Qu, Y., Zhao, L., & Moore, J. C. (2023). Thermosteric and dynamic sea level under solar geoengineering. *npj Climate and Atmospheric Science*, *6*(1), 135.*Abstract*The IPCC sixth assessment report forecasts sea level rise (SLR) of up to 2 m along coasts by 2100 relative to 1995–2014 following business as usual (SSP585) scenarios. Geoengineering may reduce this threat. We use five Earth System Models simulations of two different solar geoengineering methods (solar dimming and stratospheric sulfate aerosol injection), that offset radiative forcing differences between SSP585 “no-mitigation” and the modest mitigation SSP245 greenhouse gas scenarios, to analyze the impact on global mean thermosteric and dynamic regional sea levels. By 2080–2099, both forms of geoengineering reduce global mean thermosteric sea level by 36–41% (11.2–12.6 cm) relative to SSP585, bringing the global mean SLR under SSP585 in line with that under SSP245, but do not perfectly restore regional SLR patterns. Some of the largest reductions (∼18 cm) are on densely populated coasts of eastern Northern America and Japan and along vulnerable Arctic coastal permafrost. Unexpected failure of regional marine cloud brightening in a warmer world <https://www.researchsquare.com/article/rs-3250111/v1> Ricke, K., Wan, J., Chen, C. C. J., Tilmes, S., Luongo, M., & Richter, J. (2023). Unexpected failure of regional marine cloud brightening in a warmer world.Abstract Marine cloud brightening is a solar geoengineering1–3 proposal to cool atmospheric temperatures and reduce some impacts of climate change. To-date, modeling studies of solar geoengineering have primarily focused on large-scale schemes with objectives of stabilizing or mediating changes in global mean temperature4–7. However, these global proposals pose substantial governance challenges8–10, making regional interventions tailored toward targeted climate outcomes potentially more attractive in the near-term. In this study, we investigate the efficacy of regional marine cloud brightening in the North Pacific designed to mitigate extreme heat in the Western United States. We find cloud brightening in a remote mid-latitude region cools our target region more than brightening in a proximate subtropical region, but both schemes reduce the relative risk of dangerous summer heat exposure under present-day conditions, by 39% and 25% respectively. However, the same cloud brightening interventions under mid-century warming produce significantly hotter rather than cooler summers, both in the Western U.S. and other areas of the world. We trace this loss of efficacy to a nonlinear response of the Atlantic Meridional Overturning Circulation to the combination of greenhouse gas driven warming and regional cloud brightening. Our result demonstrates a risk in assuming that regional interventions that are effective under certain conditions will remain effective as the climate continues to change. ------------------------------ WORKING PAPERSUncertain Remedies to Fight Uncertain Consequences: The Case of Solar Geoengineering <https://www.rff.org/publications/working-papers/uncertain-remedies-to-fight-uncertain-consequences-the-case-of-solar-geoengineering/> *Abstract*Solar geoengineering can cool our planet and counteract the warming caused by greenhouse gas emissions. Given current emission trajectories, solar geoengineering has the potential to save lives, reduce severe impacts on economic production, and save ecosystems and island states. Deterministic integrated assessment models tend to show major benefits from solar geoengineering, but are highly sensitive to the assumed and highly uncertain damages from solar geoengineering as well as the effectiveness of cooling the planet. We analyze how uncertainties and the anticipation of learning change the case for solar geoengineering in a world with an uncertain temperature response to carbon dioxide emissions. International Climate Agreements under The Threat of Solar Geoengineering <https://www.rff.org/publications/working-papers/international-climate-agreements-under-the-threat-of-solar-geoengineering/> *Abstract*The possibility of overshooting global emissions targets has triggered a public debate about the role solar geoengineering (SGE) - using technologies to reflect solar radiation away from Earth - may play in managing climate change. One major concern is that SGE technologies are relatively cheap, and could potentially be deployed by a single nation (the “free driver”) that could effectively control the global climate. Another concern is that SGE opportunities may alter countries’ incentives to cooperate on abatement. Here we develop a game-theoretic model to analyze how opportunities to deploy SGE impact global abatement and the effectiveness of international environmental agreements (IEAs) on climate change. We show that non-cooperative abatement levels may increase or decrease under the threat of SGE, depending on how damaging the free-driver’s level of deployment is on others. We also show the stability of IEAs that govern abatement is challenged by two competing strategic incentives. One is a familiar free-rider incentive, which is the benefit a country earns by leaving an agreement and lowering its abatement. The other incentive is the benefit a country earns by joining an agreement and increasing abatement in order to motivate the free-driver to reduce its level of deployment. We introduce the term anti-driver to describe this second incentive. Ultimately, we find that if the anti-driver incentives are high enough, the threat of SGE can expand both the depth (i.e., abatement level) and breadth (i.e., participation level) of stable IEAs compared to a world without SGE. ------------------------------ WEB POSTS <https://www.rff.org/publications/working-papers/international-climate-agreements-under-the-threat-of-solar-geoengineering/>Chris Sacca's plan to salt the Earth <https://www.axios.com/pro/climate-deals/2023/09/21/chris-sacca-lowercarbon-al-gore-geoengineering>Geoengineering & Human Rights —Authoritative statements and language from recent human rights expert reports <https://www.ciel.org/news/media-brief-geoengineering-human-rights/>*Move Smoke to Cool Earth <https://makesunsets.com/blogs/news/move-smoke-to-cool-earth>*It’s Time to Engineer the Sky <https://www.scientificamerican.com/article/its-time-to-engineer-the-sky/> <https://www.scientificamerican.com/article/its-time-to-engineer-the-sky/> ------------------------------ REPORTSGlobal status of activities relating to Solar Radiation Modification and its governance <http://carnegiecouncil.co/44YaJ2n> ------------------------------ PODCASTSBlot Out the Sun? / Luke Iseman & Andrew Song | Tallberg Foundation <https://tallbergfoundation.org/podcasts/blot-out-the-sun/> *“Luke Iseman and Andrew Song explain how they think they can cool the planet.”* Does SRM's location affect global temperature? Zhang | Reviewer 2 does geoengineering Does SRM's location affect global temperature? Zhang Reviewer 2 does geoengineering 1:05:52 <https://podcasts.apple.com/us/podcast/does-srms-location-affect-global-temperature-zhang/id1529459393?i=1000629046782&uo=4> “The Radiative Forcing Pattern Effect on Climate Sensitivity*https://essopenarchive.org/users/535851/articles/655683-the-radiative-forcing-pattern-effect-on-climate-sensitivity <https://essopenarchive.org/users/535851/articles/655683-the-radiative-forcing-pattern-effect-on-climate-sensitivity>”* ------------------------------ *UPCOMING EVENTS**Making well-informed decisions about solar radiation modification by Carnegie Climate Governance Initiative (C2G), UNESCO, The Energy and Resources Institute (TERI), The Degrees Initiative <https://sciencesummitunga78.sched.com/event/1O4is> | 26 September 2023**Solar Geoengineering Futures: Interdisciplinary Research to Inform Decisionmaking by Resources for Future <https://www.rff.org/events/conferences/solar-geoengineering-futures-current-research-and-uncertainties/> | 28-29 September 2023**Conference—Solar Geoengineering Futures: Current Research and Uncertainties by Resources for the Future (RFF) <https://www.rff.org/events/conferences/solar-geoengineering-futures-current-research-and-uncertainties/>| 28-29 September 2023**Perspectives on Solar Radiation Management Governance by Geneva Environment Network <https://www.genevaenvironmentnetwork.org/events/perspectives-on-solar-radiation-management-governance/> | 12 October 2023**Climate Engineering (GRS) <https://www.grc.org/climate-engineering-grs-conference/2024/>| 17-18 February 2024**GRC Climate Engineering 2024 <https://www.grc.org/climate-engineering-conference/2024/>| 18-23 February 2024* ------------------------------ *DEADLINES**PhD opportunity at University of Tasmania | Research Title: Solar Radiation Management in Antarctica: International Law and Policy Implications <https://www.utas.edu.au/research/degrees/available-projects/projects/law/antarctic-solar-radiation-management> | Deadline: 25 September 2023**The Climate Intervention Environmental Impact Fund <https://cieif.org/> | Application Deadline: 01 November 2023* ------------------------------ -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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