Cost-Risk Trade-Off of Mitigation and Solar Geoengineering: Considering Regional Disparities Under Probabilistic Climate Sensitivity

Abstract

Solar geoengineering (SGE) constitutes a viable option to ameliorate anthropogenic temperature rise. However, it does not simultaneously compensate for anthropogenic changes in further climate variables in a perfect manner. Here, we investigate to what extent a proponent of the 2 °C-temperature target would apply SGE in conjunction with mitigation in view of regional disparities in temperature and precipitation. We apply cost-risk analysis (CRA), which is a decision analytic framework that trades-off expected welfare-loss from climate policy costs and climate risks from transgressing a climate target. Here, in ‘Giorgi’-regional-scale analyses, we evaluate the optimal mix of SGE and mitigation under probabilistic information about climate sensitivity and generalize CRA in order to include regional temperature and precipitation risks. In addition to a mitigation-only analysis, social welfare is maximized for the following three joint-mitigation-SGE scenarios: temperature-risk-only, precipitation-risk-only, and equally weighted both-risks. We find that for regionally differentiated precipitation targets, the usage of SGE will be restricted. Our results indicate that SGE would save 70–75% of welfare-loss in the precipitation-risk-only and both-risks scenarios compared to a purely mitigation-based analysis with approximate overall welfare loss of 4% in terms of balanced growth equivalent from economic costs and climate risks.