A new study led by researchers at the University of Cape Town (UCT) found that stratospheric aerosol injection (SAI) – a technology designed to cool the planet by reflecting sunlight into space – could substantially reduce Africa’s soaring temperatures. But it wouldn’t be enough to shield the continent from the growing risks of heat stress.
While the findings, published in Environmental Research: Climate, showed that SAI could offset more than 85% of climate change’s impact on heat stress hazards, the intervention would reduce overall heat stress risk by less than 38%. Population growth, poverty, ageing infrastructure and social vulnerability mean millions of Africans would remain at risk, even in a cooler climate.
The study concludes that technological interventions cannot substitute for investments in adaptation and development.
“Climate intervention may reduce temperatures, but it cannot eliminate the underlying conditions that make people vulnerable,” says Professor Babatunde Abiodun, the study’s corresponding author and director of the Nansen-Tutu Centre for Marine Environmental Research at UCT. “Our findings showed that heat stress risk is not simply a climate problem. It is also a development challenge. Unless countries strengthen healthcare systems, improve living conditions, expand access to cooling, and build more resilient communities dangerous heat will continue to threaten lives and livelihoods.”
Heat stress is becoming one of Africa’s most pressing public health and economic challenges.
Unlike ordinary air temperature, heat stress combines heat and humidity to measure how difficult it is for the human body to cool itself. High humidity prevents sweat from evaporating efficiently, making even moderate temperatures potentially dangerous.
Across Africa, rising heat is already reducing labour productivity, straining electricity systems, threatening agricultural production, and increasing the risk of heat-related illnesses and deaths. Climate projections suggest these impacts will worsen substantially over coming decades.
To investigate whether solar geoengineering could reduce these threats, the researchers analysed climate simulations from the latest CMIP6 models – along with the ARISE-SAI experiment – which simulates injecting sulphur dioxide particles into the stratosphere to reflect a small proportion of incoming sunlight and stabilise global temperatures near 1.5°C above pre-industrial levels.
Rather than examining temperature alone, the team developed a comprehensive assessment of heat stress risk by combining three factors: the physical hazard created by heat and humidity; the number of people exposed; and their socioeconomic vulnerability. This approach paints a realistic picture of the risks facing African communities.
Under the SSP2-4.5 (a prominent climate change scenario used in global climate modelling) emissions scenario, dangerous heat stress is projected to intensify across much of the continent, particularly in West Africa, Central Africa, and humid coastal regions. These areas experience a combination of rising temperatures and persistent humidity that makes outdoor work increasingly hazardous.
Across Africa, SAI reduces population exposure by only about 25%.
The researchers also found that the benefits of geoengineering would be unevenly distributed. Coastal regions of West Africa, parts of Central Africa and Sudan continue to experience dangerous levels of heat stress despite the cooling intervention. Meanwhile, Southern Africa experiences some of the greatest reductions in heat hazards.
Perhaps more significantly, the study shows that geoengineering changes the relative heat stress rankings of African countries.
Around 65% of countries fail to return to their current risk rankings even after SAI is introduced. This finding suggests that as climate hazards decline, vulnerability becomes an even more important determinant of future heat stress.
Countries with rapidly growing populations, widespread poverty, and limited adaptive capacity remain highly vulnerable regardless of improvements in climate conditions.
“Our analysis showed that vulnerability increasingly determines who remains at greatest risk,” says Prof Abiodun. “If two countries experience similar levels of heat, the country with weaker healthcare, poorer housing, limited access to electricity, and greater socioeconomic inequality will continue to experience higher impacts.”
The findings have significant implications for international discussions on solar geoengineering.
Interest in SAI has grown rapidly in recent years as global temperatures continue to rise and efforts to reduce greenhouse gas emissions struggle to keep pace. Some scientists argue that temporarily cooling the Earth could buy valuable time while emissions are reduced.
However, critics warn that geoengineering poses significant ethical, political, and environmental uncertainties. The new study does not advocate deploying SAI, but instead evaluates how such an intervention could affect African societies if implemented.
“Our intention is not to promote geoengineering as a solution,” says Prof Abiodun. “We wanted to understand both its strengths and its limitations. Our results clearly show that any discussion about solar geoengineering must include questions about equity, vulnerability and social resilience – particularly for regions such as Africa.”
According to Prof Abiodun, governments should continue prioritising conventional climate adaptation measures including heat-health action plans, early-warning systems, climate-sensitive urban planning, improved housing, expanded access to electricity for cooling, and stronger public health services.
Because the study relies on the experimental ARISE-SAI simulations produced using a single climate model, Prof Abiodun says that the findings should not be interpreted as precise prediction.
“The findings represent scientifically plausible scenarios that improve understanding of how geoengineering could interact with social and climatic systems across Africa,” he says.