Potential impact of stratospheric aerosol geoengineering on projected temperature and precipitation extremes in South Africa

Abstract

Climate geoengineering technologies are being increasingly investigated by Earth system science researchers to mitigate climate change. Stratospheric Aerosol Injection (SAI) is one such option that is popularly debated as a potential measure to offset anthropogenic warming, while signatories of the Paris Agreement make efforts to reduce emissions and limit warming to 1.5°C. Most modelling studies to date have assessed the projected impact of SAI on global and regional scales, while a little has been done at country scale. Similarly, research into the effectiveness of varying injection characteristics is limited especially in a developing world. As a developing country rife with inequality, poverty, and disease burden, South Africa is highly susceptible to the increasing frequency and magnitude of temperature and precipitation extremes due to anthropogenic warming. The aim of this study is to investigate how SAI deployment would influence temperature and precipitation extremes over South Africa's climatic zones in the future (2075–2095). Climate model simulations from the Geoengineering Large Ensemble (GLENS) project are used to conduct a comparative analysis of what a future with and without SAI (under Representative Concentration Pathway 8.5 (RCP8.5) would look like in South Africa. Using a selection of extreme temperature and precipitation indices from the “Expert Team on Climate Change Detection and Indices” (ETCCDI), the impact of three SAI feedback experiments (GLENS, Equatorial SAI and Lower SAI) is investigated to provide insight into the effectiveness of different injection characteristics. The results indicate that in a future without SAI, the frequency of hot nights (TN90P: +45-60%) and hot days (TX90P: +15-50%) would increase, with north-east SAF projected to become the most vulnerable to extreme warming. Heavy precipitation days (R10MM) and total precipitation (PRCPTOT) are projected to decrease across most SAF's climatic zones (–0.5-2 days/year and –20-70 mm/year, respectively). The KwaZulu-Natal coast is the only region with projected increases in the number of heavy precipitation days and total precipitation (up to +2.5 days/year and +70 mm/year, respectively), and subsequent flood conditions. Overall, all three SAI feedback experiments (to varying degrees) are projected to reduce temperature and precipitation anomalies over SAF. SAI is projected to trigger a nationwide cooling effect with increased frequency of cool nights (TN10P: +1-4%) and cool days (TX10P: up to +3%). This could alleviate heat-induced strain on human health, agricultural production, and the harsh effects of climate extremes on South Africa's most vulnerable communities. The projected general reductions in PRCPTOT (–10-60%) and R10MM (–1-4 days/year) could have negative implications for water security and agricultural production for the country. Injecting sulfate aerosols into the Equatorial and Lower stratosphere could cause larger decreases in precipitation extremes than in the feedback experiment. These findings should be read with caution as they are specific to the types of SAI deployed in the GLENS project.