Geoengineering to prevent the worst impacts of climate breakdown could expose up to a billion more people to malaria, scientists have found.
The report, published in Nature Communications, is the first assessment of how geoengineering the climate could affect the burden of infectious diseases.
Geoengineering includes removing carbon dioxide from the sky so the atmosphere will trap less heat, and solar radiation management (SRM) – reflecting more sunlight away from the planet so less heat is absorbed in the first place. The latter could be done in various ways, including spraying particles into the sky to reflect the sun away from the earth.
This study looked at the latter, specifically injecting aerosols into the stratosphere that reflect incoming sunlight, thereby temporarily “pausing” global warming. Though SRM is often discussed as a way to reduce climate injustice, its potential impacts on health have seldom been studied.
Scientists modelled 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 genus of mosquito and identify how many people live in areas where transmission is possible.
They found that in some areas, the high temperatures predicted killed the malaria parasite, so rapidly cooling the area could reverse those declines, leading to a rise in the disease. In the high warming scenario, simulations found that a billion extra people were at risk of malaria in the geoengineered world.
“The implications of the study for decision-making are significant,” said Colin Carlson an assistant research professor at Georgetown University Medical Center and lead author of the study. “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 populations on the frontlines of climate change, we should be able to add up the risks and benefits — especially in terms of neglected health burdens, such as mosquito-borne disease.”
Other findings include that geoengineering could reduce malaria in some places while increasing it in others. For example, in both scenarios, the authors found that geoengineering might substantially reduce malaria risk in the Indian subcontinent even compared with the present day. However, that protective effect would be offset with an increase in risk in south-east Asia.
“On a planet that’s too hot for humans, it also gets too hot for the malaria parasite,” says Carlson. “Cooling the planet might be an emergency option to save lives, but it would also reverse course on those declines.”