| Subscribe to Geoengineering Updates Substack here: WEEKLY SUMMARY (13 NOVEMBER - 19 NOVEMBER 2023)
DEADLINES
RESEARCH PAPERSYuan, T., Song, H., Wood, R., Oreopoulos, L., Platnick, S., Wang, C., ... & Wilcox, E. (2023). Observational evidence of strong forcing from aerosol effect on low cloud coverage. Science Advances, 9(45), eadh7716.AbstractAerosols cool Earth’s climate indirectly by increasing low cloud brightness and their coverage (Cf), constituting the aerosol indirect forcing (AIF). The forcing partially offsets the greenhouse warming and positively correlates with the climate sensitivity. However, it remains highly uncertain. Here, we show direct observational evidence for strong forcing from Cf adjustment to increased aerosols and weak forcing from cloud liquid water path adjustment. We estimate that the Cf adjustment drives between 52% and 300% of additional forcing to the Twomey effect over the ocean and a total AIF of −1.1 ± 0.8 W m−2. The Cf adjustment follows a power law as a function of background cloud droplet number concentration, Nd . It thus depends on time and location and is stronger when Nd is low. Cf only increases substantially when background clouds start to drizzle, suggesting a role for aerosol-precipitation interactions. Our findings highlight the Cf adjustment as the key process for reducing the uncertainty of AIF and thus future climate projections.
Laakso, A., Visioni, D., Niemeier, U., Tilmes, S., & Kokkola, H. (2023). Dependency of the impacts of geoengineering on the stratospheric sulfur injection strategy part 2: How changes in the hydrological cycle depend on injection rates and model?. EGUsphere, 2023, 1-29.AbstractThis is the second of two papers where we study the dependency of the impacts of stratospheric sulfur injections on the used model and injection strategy. Here, aerosol optical properties from simulated stratospheric aerosol injections using two aerosol models (modal scheme M7 and sectional scheme SALSA), as described in Part 1, are implemented consistently into EC-Earth, MPI-ESM and CESM Earth System Models to simulate the climate impacts of different injection rates ranging from 2 to 100 Tg(S)yr−1. Two sets of simulations were simulated with the three ESMs: 1) Regression simulations, where abrupt change in CO2 concentration or stratospheric aerosols over preindustrial conditions were applied to quantify global mean fast temperature independent climate responses and quasi-linear dependence on temperature and 2) equilibrium simulations, where radiative forcing of aerosol injections with various magnitudes compensate the corresponding radiative forcing of CO2 enhancement to study the dependence of precipitation on the injection magnitude; the latter also allow to explore the regional climatic responses. Large differences in SALSA and M7 simulated radiative forcings in Part 1 translated into large differences in the estimated surface temperature and precipitation changes in ESM simulations: e.g. an injection rate of 20 Tg(S)yr−1 in CESM using M7 simulated aerosols led to only 2.2 K global mean cooling while EC-Earth – SALSA combination produced 5.2 K change. In equilibrium simulation, where aerosol injections were used to compensate for radiative forcing of 500 ppm atmospheric CO2 concentration, global mean precipitation reduction varied between models from -0.7 to - 2.4 %. These precipitation changes can be explained by the fast precipitation response due to radiation changes caused by the stratospheric aerosols and CO2 because global mean fast precipitation response is rather negatively correlated with global mean absorbed radiation. Our study shows that estimating the impact of stratospheric aerosol injection on climate is not straightforward. This is because the capability of the sulfate layer to reflect solar radiation and absorb LW radiation is sensitive to the injection rate as well as the aerosol model used to simulate the aerosol field. These findings emphasize the necessity for precise simulation of aerosol microphysics to accurately estimate the climate impacts of stratospheric sulfur intervention. This study also reveals gaps in our understanding and uncertainties that still exist related to these controversial techniques.
Taylor, G. M., Wadhams, P., Visioni, D., Goreau, T., Field, L., & Kuswanto, H. (2023). Bad science and good intentions prevent effective climate action.AbstractAlthough the 2015 Paris Agreement climate targets seem certain to be missed, only a few experts are questioning the adequacy of the current approach to limiting climate change and suggesting that additional approaches are needed to avoid unacceptable catastrophes. This article posits that selective science communication and unrealistically optimistic assumptions are obscuring the reality that greenhouse gas emissions reduction and carbon dioxide removal will not curtail climate change in the 21st Century. It also explains how overly pessimistic and speculative criticisms are behind opposition to considering potential climate cooling interventions as a complementary approach for mitigating dangerous warming.
There is little evidence supporting assertions that: current greenhouse gas emissions reduction and removal methods can and will be ramped up in time to prevent dangerous climate change; overshoot of Paris Agreement targets will be temporary; net zero emissions will produce a safe, stable climate; the impacts of overshoot can be managed and reversed; Intergovernmental Panel on Climate Change models and assessments capture the full scope of prospective disastrous impacts; and the risks of climate interventions are greater than the risks of inaction.
These largely unsupported presumptions distort risk assessments and discount the urgent need to develop a viable mitigation strategy. Due to political pressures, many critical scientific concerns are ignored or preemptively dismissed in international negotiations. As a result, the present and growing crisis and the level of effort and time that will be required to control and rebalance the climate are severely underestimated.
In conclusion, the paper outlines the key elements of a realistic policy approach that would augment current efforts to constrain dangerous warming by supplementing current mitigation approaches with climate cooling interventions.
Hueholt, D., Barnes, E., Hurrell, J., & Morrison, A. (2023). Climate speeds help frame relative ecological risk in future climate change and stratospheric aerosol injection scenarios.AbstractStratospheric aerosol injection (SAI) is a potential method of climate intervention to reduce climate risk as decarbonization efforts continue. Two recent Earth system modeling experiments depict policy-relevant SAI scenarios with similar temperature targets (near 1.5°C), but with deployment delayed by 10 years between experiments. This relatively short delay leads to highly distinct profiles of ecological risk from climate speeds. Climate speeds when global temperature is maintained with SAI are indistinguishable on a planetary scale from those experienced under preindustrial conditions. In contrast, the delayed SAI deployment produces very large climate speeds far beyond natural variability and robustly greater in magnitude over land than no-SAI climate change with present policy. Examining the global area exposed to threshold climate speeds facilitates evaluation of relative ecological risk among future climate scenarios. Our results support discussion of tradeoffs and timescales in future climate intervention scenario design and decision-making.
Goddard, P. B., Kravitz, B., MacMartin, D. G., Visioni, D., Bednarz, E. M., & Lee, W. R. (2023). Stratospheric aerosol injection can reduce risks to Antarctic ice loss depending on injection location and amount. Journal of Geophysical Research: Atmospheres, 128(22), e2023JD039434.AbstractOwing to increasing greenhouse gas emissions, the Antarctic Ice Sheet is vulnerable to rapid ice loss in the upcoming decades and centuries. This study examines the effectiveness of using stratospheric aerosol injection (SAI) that minimizes global mean temperature (GMT) change to slow projected 21st century Antarctic ice loss. We simulate 11 different SAI cases which vary by the latitudinal location(s) and the amount(s) of the injection(s) to examine the climatic response near Antarctica in each case as compared to the reference climate at the turn of the last century. We demonstrate that injecting at a single latitude in the northern hemisphere or at the Equator increases Antarctic shelf ocean temperatures pertinent to ice shelf basal melt, while injecting only in the southern hemisphere minimizes this temperature change. We use these results to analyze the results of more complex multi-latitude injection strategies that maintain GMT at or below 1.5°C above the pre-industrial. All these multi-latitude cases will slow Antarctic ice loss relative to the mid-to-late 21st century SSP2-4.5 emissions pathway. Yet, to avoid a GMT threshold estimated by previous studies pertaining to rapid West Antarctic ice loss (1.5°C above the pre-industrial GMT, though large uncertainty), our study suggests SAI would need to cool about 1.0°C below this threshold and predominately inject at low southern hemisphere latitudes (∼15°S - 30°S). These results highlight the complexity of factors impacting the Antarctic response to SAI and the critical role of the injection strategy in preventing future ice loss.
Rosenthal, S., Irvine, P. J., Cummings, C. L., & Ho, S. S. (2023). Exposure to climate change information predicts public support for solar geoengineering in Singapore and the United States. Scientific Reports, 13(1), 19874.AbstractSolar geoengineering is a controversial climate policy measure that could lower global temperature by increasing the amount of light reflected by the Earth. As scientists and policymakers increasingly consider this idea, an understanding of the level and drivers of public support for its research and potential deployment will be key. This study focuses on the role of climate change information in public support for research and deployment of stratospheric aerosol injection (SAI) in Singapore (n = 503) and the United States (n = 505). Findings were consistent with the idea that exposure to information underlies support for research and deployment. That finding was stronger in the United States, where climate change is a more contentious issue, than in Singapore. Cost concern was negatively related to support for funding and perceived risk was negatively related to support for deployment. Perceived government efficacy was a more positive predictor of support for funding in Singapore than in the United States. Additionally, relatively low support for local deployment was consistent with a NIMBY mindset. This was the first study to quantify the role of climate change information in SAI policy support, which has practical implications for using the media and interpersonal channels to communicate about SAI policy measures.
Virgin, J. G., & Fletcher, C. G. (2023). Declining Geoengineering Efficacy Caused by Cloud Feedbacks in Transient Solar Dimming Experiments. Journal of Climate.AbstractSolar radiation modification (SRM) with injections of aerosols into the stratosphere has emerged as a research area of focus with the potential to cool the planet. However, the amount of SRM required to achieve a given level of cooling, and how this relationship evolves in response to increasing greenhouse gas emissions, remains uncertain. Here, we explore the evolution of solar dimming efficacy over time by defining and quantifying a new SRM feedback term, which is analogous to conventional radiative feedbacks. Using Earth System Model simulations that dynamically adjust the amount of insolation to offset global mean warming from increasing CO2, we find that positive SRM feedbacks decrease global planetary albedo and diminish the efficacy of solar dimming. Physically, the decrease in albedo is primarily due to reductions in optically thick tropical cloud fraction in the boundary layer and mid troposphere, which is driven by a drying and destabilization of the tropical mid to lower troposphere. These results offer an energetic explanation for reduced cloud fraction commonly observed in idealized SRM experiments, as well as reaffirm the need to understand the troposphere response, particularly from clouds, in realizable geoengineering experiments and their potential to feed back onto SRM efficacy.
WEB POSTS
REPORTS
UPCOMING EVENTS
YOUTUBE VIDEOSSolar Climate Intervention Virtual Symposium 7 (Chen Xing & Dr. David Mitchell) | Solar Climate Intervention Talks “Solar Climate Intervention Virtual Symposium 7 Chen Xing (University of California Santa Barbara): "Why does Marine Cloud Brightening dampen El Niño–Southern Oscillation?"Dr. David Mitchell (Desert Research Institute, USA) : "Clearing Logjams in CCT Research"”
What is solar radiation modification governance? | SRM Youth Watch “Loann Marquant shares insights on the governance of Solar Radiation Modification during the launch event of SRM Youth Watch at New York Climate Week.”
How can stratospheric aerosol injection cool the planet? | SRM Youth Watch “Alice Wells explains how stratospheric aerosol injection can cool the planet at the launch event of Solar Radiation Modification Youth Watch during New York Climate Week.”
What power dynamics could jeopardize Solar Radiation Modification governance discussions? | SRM Youth Watch “This video is an excerpt from the Solar Radiation Modification Youth Watch launch event, which took place during New York Climate Week. Prisha Kumar, a co-founder of the Institute for Climate Policy Solutions, was one of the panelists and shared her insights on how power dynamics could potentially jeopardize discussions on Solar Radiation Modification governance.”
What does the intergovernmental panel on Climate Change say about Solar Radiation Modification? | SRM Youth Watch “Thelma Krug, the former Vice Chair of the IPCC, shares insights at SRM Youth Watch Launch event during New York Climate Week.”
 
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