Estimating option values of solar radiation management assuming that climate sensitivity is uncertain

Abstract

Although solar radiation management (SRM) might play a role as an emergency geoengineering measure, its potential risks remain uncertain, and hence there are ethical and governance issues in the face of SRM's actual deployment. By using an integrated assessment model, we first present one possible methodology for evaluating the value arising from retaining an SRM option given the uncertainty of climate sensitivity, and also examine sensitivities of the option value to SRM's side effects (damages). Reflecting the governance challenges on immediate SRM deployment, we assume scenarios in which SRM could only be deployed with a limited degree of cooling (0.5°C) only after 2050, when climate sensitivity uncertainty is assumed to be resolved and only when the sensitivity is found to be high (T2x = 4°C). We conduct a cost-effectiveness analysis with constraining temperature rise as the objective. The SRM option value is originated from its rapid cooling capability that would alleviate the mitigation requirement under climate sensitivity uncertainty and thereby reduce mitigation costs. According to our estimates, the option value during 1990-2049 for a +2.4°C target (the lowest temperature target level for which there were feasible solutions in this model study) relative to preindustrial levels were in the range between $2.5 and $5.9 trillion, taking into account the maximum level of side effects shown in the existing literature. The result indicates that lower limits of the option values for temperature targets below +2.4°C would be greater than $2.5 trillion.solar radiation management | option value | climate sensitivity | uncertainty | decision tree analysis U ncertainties surrounding equilibrium climate sensitivity (T2x) (1) pose a challenge to mitigation policymaking aimed at achieving the goal of limiting the temperature rise below certain levels (e.g., +2°C relative to preindustrial levels). The inertia of temperature rise would demand more stringent mitigation policy over the period of climate sensitivity uncertainty in preparation for possible occurrence of high climate sensitivity, because it is difficult to reduce emissions sufficiently rapidly even with all of the currently available technologies of mitigation.The possibility of higher climate sensitivity (2) and the inability to instantaneously control the temperature via mitigation have sparked positive debates about solar radiation management (SRM), especially about conducting research and development (R&D) on the topic (3, 4). SRM has been regarded as a rapid (5) and relatively inexpensive geoengineering measure compared with mitigation; in this study, our cost estimates are based on albedo enhancement via stratospheric sulfur injections (Materials and Methods). However, SRM's overall costs would be higher than simply the deployment costs alone when its environmental risks (6, 7) [e.g., polar ozone depletion (4, 8), changes in precipitation patterns (9)] are factored in, although the true magnitude of all of the risks is still unknown. Moreover, SRM cann...

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

“…In fact, on the order of a thousand scenarios are assembled in the latest IPCC report [27], that are based on climate targets in conjunction with CEA, rather than on CBA. Emmerling and Tavoni [22], Arino et al [28], Ekholm and Korhonen [29], Stankoweit et al [30], and Khabbazan et al [31] evaluated SRM together with mitigation applying CEA. With this article, we aim to serve those readers who acknowledge value in utilizing climate targets as entry assumptions for further economic analysis.…”

How geoengineering scenarios frame assumptions and create expectations

“…Absent from these scenarios are for example extreme natural events, the interplay between social and physical factors, metrics other than average temperatures, elements that study 'how' to geoengineer (not just 'what if'), partial or regional SRM deployment, or multiple different technologies deployed in parallel. However, recent papers indicate that this is starting to change: Keith and Irvine (2016) and Arino et al (2016) explore SRM scenarios that offset only part of the warming; Cao et al (2017) model a 'cocktail' scenario combining two geoengineering methods; and Kleinschmitt et al (2017) explore the sensitivity of radiative forcing to the aerosol injection strategy. The 'silver bullet' approach is techno-optimistic.…”

Solar geoengineering could substantially reduce climate risks—A research hypothesis for the next decade

“…Tens of climate model studies have been published, including at least 25 from the Geoengineering Model Intercomparison Project (GeoMIP) [ Kravitz et al ., ], an effort to evaluate standard SG experiments that has seen over 15 climate modeling groups participate. Scientific and technical evaluations of the stratospheric aerosol geoengineering proposal that Crutzen discussed have been made and continue to support the view that a substantial negative radiative forcing could be achieved [ Boucher et al ., ] and at a cost of tens of billions of dollars per year [ Robock et al ., ; McClellan et al ., ; Arino et al ., ]. Studies have explored the side‐effects on stratospheric ozone [e.g., Tilmes et al ., ; Pitari et al ., ], on the quality of light [ Kravitz et al ., ], and on the deposition of released aerosols [ Kravitz et al ., ; Eastham , ].…”