Geoengineering or making large-scale interventions in the Earth's climate system to reverse the effects of climate change would have massive repercussions for the health of billions living in tropical countries with malaria, revealed a recent study.
One billion extra people could be at risk of malaria in a geoengineered world, revealed the study titled "Solar geoengineering could redistribute malaria risk in developing countries," published on 20 April 2022 in Nature Communications.
Scientists from icddr,b and other research institutions – led by Colin Carlson, assistant research professor at the Centre for Global Health Science and Security at Georgetown University Medical Center – conducted the study to understand how solar radiation management (SRM) geoengineering could affect some of the world's poorest and most vulnerable regions.
Some researchers have suggested that it may be possible to temporarily "pause" global warming by injecting aerosols into the stratosphere that reflect incoming sunlight. Though SRM is often discussed as a way to reduce climate injustice, its potential impacts on health have barely been studied, said a press release from icddr,b.
In the study, a team of eight researchers from the United States, Bangladesh, South Africa, and Germany used climate models to simulate what malaria transmission could look like in two future scenarios, with medium or high levels of global warming, with and without geoengineering.
The models identify which temperatures are most conducive for transmission by the Anopheles mosquito vectors, and identify how many people live in areas where transmission is possible.
In both scenarios, malaria risk was predicted to shift significantly between regions; but in the high warming scenario, simulations found that a billion extra people were at risk of malaria in a geoengineered world.
"In a planet that's too hot for humans, it also gets too hot for the malaria parasite," said Carlson. "Cooling the planet might be an emergency option to save lives, but it would also reverse course on those declines."
Mohammad Shafiul Alam, a malaria specialist at icddr,b, said, "This is the first of its kind study that examined the likely impact of geoengineering techniques on vector borne diseases. It revealed that if such techniques are implemented it may well cut both ways: some countries will benefit and other countries will suffer."
The study follows a 2018 commentary on Climate Change in Nature by Carlson and the study's senior author, Christopher Trisos, a senior researcher at the University of Cape Town.
In the commentary, the researchers proposed a hypothesis now confirmed in the new study: because malaria transmission peaks at 25°C, cooling the tropics using geoengineering might ultimately increase malaria risk in some places relative to not only alternative futures, but also the present day.
"The potential for geoengineering to reduce risks from climate change remains poorly understood, and it could introduce a range of new risks to people and ecosystems," said Trisos.
"Geoengineering might save lives, but the assumption that it will do so equally for everyone might leave some countries at a disadvantage when it comes time to make decisions. If geoengineering is about protecting frontline populations, we should be able to add up the risks and benefits — especially in terms of neglected health burdens like mosquito-borne disease," he added.
Carlson said one of the most surprising findings was the scale of potential trade-offs between regions. For example, in both scenarios, the authors found that geoengineering might substantially reduce malaria risk in the Indian subcontinent even compared to the present day.
However, that protective effect would be offset with an increase in risk in southeast Asia. For decision-makers, this might complicate the geopolitical reality of climate intervention.
"We're so early in this process that the conversation is still about increasing Global South leadership in geoengineering research. Our study highlights that the frontlines of climate injustice are not one monolithic bloc, especially when it comes to health," said Carlson.