Scale Invariant Turbulence and Gibbs Free Energy in the Atmosphere

A method of calculating the Gibbs Free Energy (Exergy) for the Earth’s atmosphere using statistical multifractality — scale invariance - is described, and examples given of its application to the stratosphere, including a methodology for extension to aerosol particles. The role of organic molecules in determining the radiative transfer characteristics of aerosols is pointed out. These methods are discussed in the context of the atmosphere as an open system far from chemical and physical equilibrium, and used to urge caution in deploying “solar radiation management”.

How can solar geoengineering and mitigation be combined under climate targets?

So far, scientific analyses have mainly focused on the pros and cons of solar geoengineering or solar radiation management (SRM) as a climate policy option in mere isolation. Here, we put SRM into the context of mitigation by a strictly temperature-target-based approach. As the main innovation, we present a scheme that extends the applicability regime of temperature targets from mitigation-only to SRM-mitigation analyses. We explicitly account for one major category of side effects of SRM while minimizing economic costs for complying with the 2 ∘C temperature target. To do so, we suggest regional precipitation guardrails that are compatible with the 2 ∘C target. Our analysis shows that the value system enshrined in the 2 ∘C target leads to an elimination of most of the SRM from the policy scenario if a transgression of environmental targets is confined to 1/10 of the standard deviation of natural variability. Correspondingly, about half to nearly two-thirds of mitigation costs could be saved, depending on the relaxation of the precipitation criterion. In addition, assuming a climate sensitivity of 3 ∘C or more, in case of a delayed enough policy, a modest admixture of SRM to the policy portfolio might provide debatable trade-offs compared to a mitigation-only future. Also, in our analysis which abstains from a utilization of negative emissions technologies, for climate sensitivities higher than 4 ∘C, SRM will be an unavoidable policy tool to comply with the temperature targets. The economic numbers we present must be interpreted as upper bounds in the sense that cost-lowering effects by including negative emissions technologies are absent. However, with an additional climate policy option such as carbon dioxide removal present, the role of SRM would be even more limited. Hence, our results, pointing to a limited role of SRM in a situation of immediate implementation of a climate policy, are robust in that regard. This limitation would be enhanced if further side effects of SRM are taken into account in a target-based integrated assessment of SRM.

Southeast Asian expert perceptions of solar radiation management techniques and carbon dioxide removal approaches: caution, ambivalence, risk precaution, and research directions

As the climate crisis intensifies in its impacts, discussions around the deployment of geoengineering solutions in case other interventions fail or prove insufficient have figured in research and have even been on the agenda of the United Nations. There have been calls for more investigation of geoengineering techniques to address the climate crisis. Yet, this response presents technological unknowns and economic, political, and ethical risks. Producing knowledge on these techniques has been pushed in many research institutes in the global North, especially in the United States, Europe, and Australia. Still, contributions from global South researchers, including those in Southeast Asia, remain scant. This paper describes the responses of seventeen climate and energy experts from southeast Asia on a purposively designed survey that collected expert opinions on two geoengineering techniques: solar radiation modification (SRM) and carbon dioxide removal (CDR), their risks, impacts, and governance as they pertain to their countries and region. Respondents showed ambivalence towards these techniques, with many supporting ‘natural’ CDR research and deployment while being cautious about ‘technological’ SRM and CDR research and deployment. Although respondents would welcome research on these technologies, especially their risks and impacts, they also identified critical barriers in research capacity development and funding availability.

The Controversial One

This chapter considers solar radiation management, also known as solar geoengineering, which seeks to manipulate Earth’s climate energy balance by reducing the absorption of incoming solar energy. As the chapter explains, this approach spans a class of proposed measures that has been polarizing the community, with some advocating it as an essential means of keeping global warming within acceptable limits, while others see only grave drawbacks and dangers. The chapter describes the two approaches to limiting the absorption of solar energy: measures taken in space, between Earth and the Sun, to reflect or disperse solar radiation before it even hits Earth’s atmosphere; and measures taken in Earth’s atmosphere or at the Earth’s surface to reflect incoming solar radiation. It goes on to discuss the various proposed methods, their potential, and their drawbacks.

The Behavioral Renaissance

This chapter looks at what will be required to rebalance the radiative balance of climate at a societally acceptable level, around 1.5°C to at most 2°C warming according to the Paris Climate Agreement. The chapter outlines the complex portfolio of measures needed to achieve this: emissions reduction, new emissions avoidance, greenhouse gas removal, and potential solar radiation management. It also shows how the relative proportions of these four different classes of measures will need to be flexible through time, in response to different needs, such as a high need for emissions reduction today that may decline with time as emissions approach zero. Flexibility will also be needed in response to the emergence of new breakthroughs, challenges, cost limits, and economic and societal constraints. The chapter considers key parameters with respect to societal change and the roles of government, corporations, and consumers, and discusses routes for channeling discontent and litigation.

The Future

This chapter draws together information to discuss a vision for the future, including emissions reduction and avoidance, implementation of negative emissions technologies, solar radiation management, adaptation, and the human dimension of how to drive change. Previous chapters have shown that the current trajectory, if unchanged, will result in global temperatures far exceeding the recommended 1.5–2°C maximum increase recommended in the Paris Agreement and that current emission levels are more likely to continue than not. This chapter summarizes this information, linking it to the important role of NETs in managing future climate change and the need for investment in new technologies. The chapter then introduces Integrated Assessment Models, which are helpful in assessing the various approaches to meeting emissions targets. Finally, the chapter considers the importance of slow response and feedback processes and tipping points.

Who May Geoengineer: Global Domination, Revolution, and Solar Radiation Management

This paper uses a novel account of non-ideal political action that can justify radical responses to severe climate injustice, including and especially deliberate attempts to engineer the climate system in order reflect sunlight into space and cooling the planet. In particular, it discusses the question of what those suffering from climate injustice may do in order to secure their fundamental rights and interests in the face of severe climate change impacts. Using the example of risky geoengineering strategies such as sulfate aerosol injections, I argue that peoples that are innocently subject to severely negative climate change impacts may have a special permission to engage in large-scale yet risky climate interventions to prevent them. Furthermore, this can be true even if those interventions wrongly harm innocent people.

Dependency of the impacts of geoengineering on the stratospheric sulfur injection strategy part 1: Intercomparison of modal and sectional aerosol module

Injecting sulfur dioxide into the stratosphere with the intent to create an artificial reflective aerosol layer is one of the most studied option for solar radiation management. Previous modelling studies have shown that stratospheric sulfur injections have the potential to compensate the greenhouse gas induced warming at the global scale. However, there is significant diversity in the modelled radiative forcing from stratospheric aerosols depending on the model and on which strategy is used to inject sulfur into the stratosphere. Until now it has not been clear how the evolution of the aerosols and their resulting radiative forcing depends on the aerosol microphysical scheme used, that is, if aerosols are represented by modal or sectional distribution. Here, we have studied different spatio-temporal injections strategies with different injection magnitudes by using the aerosol-climate model ECHAM-HAMMOZ with two aerosol microphysical modules: the sectional module SALSA and the modal module M7. We found significant differences in model responses depending on the used aerosol microphysical module. In a case where SO2 was injected continuously in the equatorial stratosphere, simulations with SALSA produced 88 %–154 % higher all-sky net radiative forcing than simulations with M7 for injection rates from 1 to 1 to 100 Tg(S) yr−1. These large differences are identified to be caused by two main factors. First, the competition between nucleation and condensation: while in SALSA injected sulfur tends to produce new particles at the expense of gaseous sulfuric acid condensing on pre-existing particles, in M7 most of the gaseous sulfuric acid partitions to particles via condensation at the expense of new particle formation. Thus, the effective radii of stratospheric aerosols were 10–52% larger in M7 than in SALSA, depending on injection rate and strategy. Second, the treatment of the modal size distribution in M7 limits the growth of the accumulation mode which results in a local minimum in aerosol number size distribution between the accumulation and the coarse modes. This local minimum is in the size range where the scattering of solar radiation is most efficient. We also found that different spatial-temporal injection strategies have a significant impact on the magnitude and zonal distribution of radiative forcing. Based on simulations with various injection rate using SALSA, the most efficient studied injection strategy produced 33–42 % radiative forcing compared to the least efficient strategy while simulations with M7 showed even larger difference of 48–76 %. Differences in zonal mean radiative forcing were even larger than that. We also show that a consequent stratospheric heating and its impact on the quasi-biennial oscillation depends both on the injection strategy and the aerosol microphysical model. Overall, these results highlight a crucial role of aerosol microphysics on the physical properties of stratospheric aerosol which in turn causes significant uncertainties in estimating climate impacts of stratospheric sulfur injections.

A Scheme for Jointly Trading off Costs and Risks of Solar Radiation Management and Mitigation Under Long-Tailed Climate Sensitivity Probability Density Distributions

Side effects of “solar-radiation management” (SRM) might be perceived as an important metric when society decides on implementing SRM as a climate policy option to alleviate anthropogenic global warming. We generalize cost-risk analysis that originally trades off expected welfare loss from climate policy costs and risks from transgressing climate targets to also include risks from applying SRM. In a first step of acknowledging SRM risks, we represent global precipitation mismatch as a prominent side effect of SRM under long-tailed probabilistic knowledge about climate sensitivity. We maximize a social welfare function for the following three scenarios, considering alternative relative weights of risks: temperature-risk-only, precipitation-risk-only, and equally-weighted both-risks. Our analysis shows that in the temperature-risk-only scenario, perfect compliance with the 2 °C-temperature target is attained for all numerically represented climate sensitivities, a unique feature of SRM, but the 2 °C-compatible precipitation corridor is violated. The precipitation-risk-only scenario exhibits an approximate mirror-image of this result. In addition, under the both-risks scenario, almost 90% and perfect compliance can be achieved for the temperature and precipitation targets, respectively. Moreover, in a mitigation-only analysis, the welfare loss from mitigation cost plus residual climate risks, compared to the no-climate-policy option, is approximately 4.3% (in terms of balanced growth equivalent), while being reduced more than 90% under a joint-mitigation-SRM analysis.