Tension between reducing sea-level rise and global warming through solar-radiation management

Abstract

A study finds tension between mitigating sea-level rise and reducing the rate of temperature change through solar-radiation management. The rapid warming that would occur if solar-radiation management were to be phased out is shown to depend critically on timescales, potentially committing future generations to its long-term use once started. Geoengineering using solar-radiation management (SRM) is gaining interest as a potential strategy to reduce future climate change impacts1,2,3. Basic physics and past observations suggest that reducing insolation will, on average, cool the Earth. It is uncertain, however, whether SRM can reduce climate change stressors such as sea-level rise or rates of surface air temperature change1,4,5,6. Here we use an Earth system model of intermediate complexity to quantify the possible response of sea levels and surface air temperatures to projected climate forcings7 and SRM strategies. We find that SRM strategies introduce a potentially strong tension between the objectives to reduce (1) the rate of temperature change and (2) sea-level rise. This tension arises primarily because surface air temperatures respond faster to radiative forcings than sea levels. Our results show that the forcing required to stop sea-level rise could cause a rapid cooling with a rate similar to the peak business-as-usual warming rate. Furthermore, termination of SRM was found to produce warming rates up to five times greater than the maximum rates under the business-as-usual CO2 scenario, whereas sea-level rise rates were only 30% higher. Reducing these risks requires a slow phase-out of many decades and thus commits future generations.