Abstract
Heat stress poses a growing threat to human health and socioeconomic activities across Africa, and climate change is expected to intensify this challenge. Stratospheric Aerosol Injection (SAI) has been proposed as a geoengineering strategy to mitigate temperature-related impacts, yet its effectiveness in reducing heat stress risks remains uncertain. This study evaluates the potential impacts of SAI on heat stress risk across Africa by bias-correcting and analysing climate simulations from CMIP6 and the ARISE-SAI experiment. Heat stress was quantified using a heat index that incorporates both temperature and relative humidity, while risk was defined as a function of hazard, exposure, and vulnerability, applying alternative normalization and aggregation methods. We assessed country-level heat stress risk, ranked nations accordingly, and examined shifts in rankings under the SSP2-4.5 scenario with and without SAI intervention.
Results show that SSP2-4.5 increases the intensity and frequency of heat stress, amplifying hazards, population exposure, and overall risk. Although SAI reduces temperature and humidity, thereby offsetting some climate-driven increases, it does not fully restore safe heat stress conditions, particularly in coastal and Sudanese regions. While the efficiency of SAI in mitigating heat stress hazards over Africa is more than 85%, it is less than 26% for exposure and less than 38% for risk. Moreover, SAI fails to return about 65% of African countries to their baseline REF positions, thereby shifting the relative importance of vulnerability in determining national risk rankings.
Effective management of heat stress in Africa therefore requires holistic frameworks that balance hazard, exposure, and vulnerability. SAI should be complemented by policies that strengthen socioeconomic resilience and adaptive capacity to ensure equitable risk reduction across the continent. Given the exploratory nature of the ARISE-SAI 1.5 simulations within CESM2-WACCM6, our findings highlight plausible scenarios and mechanisms but should be interpreted as qualitative indicators rather than definitive quantitative projections.
