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RESEARCH PAPERSHenry, M., Bednarz, E. M., & Haywood, J. (2024). How Does the Latitude of Stratospheric Aerosol Injection Affect the Climate in UKESM1?. EGUsphere, 2024, 1-23. Abstract Stratospheric Aerosol Injection (SAI) refers to a climate intervention method by which aerosols are intentionally added to the lower stratosphere to enhance sunlight reflection and offset some of the adverse effects of global warming. The climate outcomes of SAI depend on the location, amount, and timing of injection, as well as the material used. Here, we isolate the role of the latitude of SO2 injection by comparing different scenarios which have the same global-mean temperature target, altitude of injection, and hemispherically symmetric injection rates. These are: injection at the equator (EQ), and injection at 15° N and S (15N+15S), at 30° N and S (30N+30S), and at 60° N and S (60N+60S). We show that injection at the equator leads to many undesirable side effects, such as a residual Arctic warming, significant reduction in tropical precipitation, reductions in high-latitude ozone, tropical lower stratospheric heating, and strengthening of the stratospheric jets in both hemispheres. Additionally, we find that the most efficient injection locations are the subtropics (15 and 30° N and S), although the 60N+60S strategy only requires around 30 % more SO2 injection for the same amount of cooling; the latter also leads to much less stratospheric warming but only marginally increases high-latitude surface cooling. Finally, while all the SAI strategies come with trade-offs, we demonstrate that the 30N+30S strategy has, on balance, the least negative side effects and is easier to implement than a multi-latitude controller algorithm; thus it is a good candidate strategy for an inter-model comparison.
Williams, B. M., Shimamoto, M. & Graumlich, L. J., (2024) “An Ethical Framework for Climate Intervention Research: What It Is and Why You Should Care”, Zygon: Journal of Religion and Science 59(1), 82–96. Abstract Climate change poses significant threats to ecosystems, human health, and global stability. Despite international efforts to reduce greenhouse gas emissions, the Earth’s climate continues to warm, leading to extreme weather events, rising sea levels, and other detrimental impacts. In response to this crisis, scientists have begun exploring various strategies to mitigate climate change through geoengineering, which involves deliberate interventions in the Earth’s climate system. This article provides an overview of climate geoengineering research, focusing on key techniques, challenges, and ethical considerations, including actions being taken by the American Geophysical Union (AGU), a nonprofit professional scientific society, to develop an ethical framework to help guide research in this important area. AGU also is driving global engagement on this topic, including with leaders and members of faith communities.
Visioni, D., & Quaglia, I. (2024, January). Changes in shipping emissions as a natural analogue for Climate Intervention: detecting and attributing changes due to specific human activities as a testbed for future controversies. In 104th AMS Annual Meeting. AMS. Abstract In 2020, new regulations from the International Maritime Organization (IMO) have resulted in a substantial reduction in the amount of SO2 emitted by vessels crossing the oceans, particularly over the Atlantic and Pacific oceans (Watson-Parris et al., 2022). Studies published before the regulations went into effect had already postulated that they would have an effect on cloud formation and direct forcing from the lack of sulfate aerosols produced, with an overall small but non-zero global impact (Jin et al., 2018). In the meantime, greenhouse gases concentrations keep rising, and there is a growing perception amongst the general public and the climate community that the latest extreme events observed have grown over the last few years: 2023 has a high likelihood of being the warmest year ever on record, while there have been record fire seasons in both Canada and Hawaii and many regions in the Northern Hemisphere have observed anomalously high sea surface temperature (SSTs), coupled with (and partially driven by) a strong positive phase of ENSO. Discussions in the news about whether some particular factors have contributed to this extreme year are growing, and many have focused on the reduction in sunlight-reflecting aerosols as a potential culprit. Such questions are strongly tied with those around the opportunity to study Sunlight Reflection Methods (SRM) as a climate intervention strategy that may ameliorate the effects of climate change by reducing incoming sunlight, perhaps using a thin layer of aerosols in the stratosphere, where they last longer and are not as harmful to people. There is robust agreement over the cooling potential of aerosols in the climate system: at the same time, there is similar agreement over the health benefits of reducing aerosol concentrations near human centers to improve public health. SRM by means of stratospheric aerosol injections (SAI) might be a proposal that ties both considerations, but in order to consider it seriously far more research is needed to reduce uncertainties and understand how the climate system would respond. In this study, we use both a range of observation spanning surface air temperatures (SAT), sea surface temperatures (SST) and top-of-atmosphere Earth Energy Imbalance (EEI) and a large ensemble of simulations performed with the Community Earth System Model (CESM2) (Simpson et al., 2023). Firstly, we will use the CESM2 LENS to understand the detection of the global signal and to attribute specific changes in regional climate, coupling available simulations with new ones where the aerosol emissions from shipping are quickly removed, as the LENS uses the Shared Socioeconomic Pathway (SSP) 3-7.0, where shipping emissions continue. The comparison of the two scenarios will provide a needed counterfactual that a simple analysis of observational datasets, considering internal variability, does not allow. However, the comparison of multiple observational datasets (such as the Berkeley temperature record and various reanalysis products such as ERA5) will also allow for a discussion of statistical significance of the detected signal based on inherent uncertainties in our knowledge of the climate system and internal climate variability. Secondly, we will expand this by simulating similar scenarios, but in which the aerosols are not removed completely but moved to the stratosphere in order to understand the projected differences between tropospheric and stratospheric aerosols in terms of regional climatic impacts. This will allow us to make more generalized conclusion around the issue of Climate Intervention (CI), in particular the combined health and climatic benefits of both removing aerosols from the troposphere, but adding them in the stratosphere so that they can cool without impacting negatively on surface air quality. This way of thinking about climate intervention will highlight the concept that CI should be thought of not as an addiction but as a vertical re-distribution of a fraction of the tropospheric aerosols, so that they can keep their benefit and reduce their negative impacts, and will help the community gain a better understanding of the limits of detectability for CI, which can better inform future governance discussions around outdoor tests.
Zhao, M., Cao, L., Visioni, D., & MacMartin, D. G. (2024). Carbon cycle response to stratospheric aerosol injection with multiple temperature stabilization targets and strategies. Earth's Future, 12(6), e2024EF004474. Abstract We analyze the global carbon cycle response to a set of stratospheric aerosol injection (SAI) simulations performed by the CESM2(WACCM6-MA) model. The simulations are performed under the specified SSP2-4.5 CO2 concentration pathway. It is found that both the temperature stabilization target and the SO2 injection strategy have important effects on the global carbon sink. Relative to the SSP2-4.5 scenario, averaged over the last 20 years of our simulations (year 2050–2069), simultaneous multi-location SO2 injection causes an increase in cumulative land carbon uptake of 45 and 23 PgC, and an increase in cumulative ocean carbon uptake of 6 and 2 PgC for temperature stabilization targets of 0.5°C and 1.5°C respectively. For a temperature stabilization target of 1.0°C, SO2 injections increase land and ocean carbon sinks by 22–42 PgC and 4–7 PgC, respectively, depending on the strategies of SO2 injections (low latitude, mid-to-high latitude, and multi-objective injection). Relative to SSP2-4.5, by year 2069, SAI increases diagnosed cumulative CO2 emissions by 25–53 PgC (3%–6%), implying a decrease in atmospheric CO2 if SO2 injections were performed under a prescribed CO2 emission pathway. Stratospheric SO2 injections slow permafrost thaw, but do not restore permafrost to the previous extent at the same warming level for all injection strategies. An abrupt termination of SO2 injection weakens both the ocean and land carbon sink, and causes a rapid decline of permafrost extent. A gradual phaseout of SO2 injection slows sharp decline of permafrost and delays the rebound of carbon sink.
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YOUTUBE VIDEOSThe Economics of Solar Radiative Management | Environmental Defense Fund Solar Climate Intervention Virtual Symposium 11 (Dr. Claudia Wieners & Dr. Daniele Visioni) | Solar Climate Intervention Talks "Solar Climate Intervention Virtual Symposium 11 Dr. Claudia Wieners (Utrecht University, Netherlands) : "Burning fossils like hell and cooling in 2080 – what could possibly go wrong? (Semi)-irreversible climate change under delayed stratospheric aerosol injection." Dr. Daniele Visioni (Cornell University, USA) : "Assessing sunlight reflection methods on the international stage: what does it mean and where are we? A perspective between science and politics."
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