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

Mohammad M Khabbazan,Hermann Held,Marius Stankoweit,Hauke Schmidt,Elnaz Roshan

doi:10.5194/esd-12-1529-2021

Abstract

Abstract. 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.

Highlights

Note that in calculating the normalized precipitation guardrails for all scenarios, the extra admissible ranges are taken into account
We performed a costeffectiveness analysis (CEA) study where solar radiation management (SRM) and mitigation are simultaneously allowed as climate policy options
We defined a scheme to include one prominent sideeffect category of SRM, regional climate pattern mismatches, in the integrated assessment, ethically consistent with the global mean temperature target. (By “pattern mismatch”, we refer to discrepancies in greenhouse-gas- and SRM-induced spatial climate anomalies for the same global mean temperature change.) For this, we defined a metric to extend the functionality of global mean temperature targets into a regime of SRM deployment

Summary

Introduction

Since Paul Crutzen has highlighted solar radiation management (SRM) as a potential climate policy option in addition to adaptation and mitigation (Crutzen, 2006), there has been increasing research on this technique as a measure to counteract anthropogenic global warming (Barrett et al, 2014; Bellamy et al, 2013; Goes et al, 2011; Irvine et al, 2012; Kravitz et al, 2013; MacMartin et al, 2014; MorenoCruz and Keith, 2013; Schmidt et al, 2012; Shepherd, 2009; Wigley, 2006). Some studies suggest that directly recommending climate policy through only CBA is challenging due to the presence of deep uncertainty about global warming impact functions (Ekholm, 2018; Kolstad et al, 2014; Kunreuther et al, 2014). These studies suggest using a target-based approach, known as costeffectiveness analysis (CEA), as long as no better data are available (Kunreuther et al, 2014; Neubersch et al, 2014)

Methods

Results

Conclusion