Snowpiercer, but Mosquitoes: Blocking Out the Sun Could Mean More Malaria

Snowpiercer, but Mosquitoes: Blocking Out the Sun Could Mean More Malaria
A mosquito chows down on an arm. (Photo: Peter Charlesworth/LightRocket, Getty Images)

New research explores how radical “fixes” to our planet’s climate could have serious side effects — including exposing millions more people to infectious diseases. This study looks at the possibility of what’s known as solar radiation management, the idea that we could use aerosols in the atmosphere to block sunlight and cool the planet back down.

Solar radiation management is a technique that is part of a larger subset of ideas called geoengineering, or biohacking the planet and atmosphere to curb runaway warming. It’s a radical idea that is slowly becoming more mainstream as we increasingly run out of time on the climate change clock.

“This idea of geoengineering revolves around emergency solutions that might reduce the impacts of climate change while we work on reducing greenhouse gas emissions,” Colin Carlson, the study’s lead author and an assistant research professor at Georgetown University Medical Centre, said in a Twitter DM. “It’s a nice thought but one of the key ideas — that it actually saves lives — hasn’t been tested nearly as much as it should be.”

To look more closely at what geoengineering could mean for public health, the researchers decided to focus on malaria, a disease with both a strong linkage to temperature changes (thanks to conditions mosquitoes need to survive) as well as serious implications for developing countries. In 2020, according to the World Health Organisation, 95% of malaria cases were in African countries, and children under 5 made up 80% of deaths. The researchers then used climate models to look at malaria transmission in a world with medium as well as high levels of global warming, and with and without geoengineering. This includes identifying the temperatures at which the malaria parasite and the mosquitoes that transmit it are likeliest to thrive, as well as the numbers of people who would be exposed in different regions.

The paper, published in Nature Communications, finds that geoengineering would create tradeoffs in malaria risk for different areas, making some places less susceptible to the disease and others more so. In the most extreme high-emissions scenario, geoengineering would put about a billion additional people at risk of malaria after rapidly cooling the places where they live. Essentially, cooling off some regions too much would push large areas of the world back to the perfect temperature for malaria transmission.

To understand what’s going on here, it’s important to know a little bit about malaria. Malaria is actually a parasite that’s spread to humans through bites from female Anopheles mosquitos. Previous research has found that malaria transmission is highest when temperatures are around 77 degrees Fahrenheit (25 degrees Celsius). In some scenarios for extreme warming, malaria risk actually decreases in some regions as the planet gets hotter. Carlson points out that this loss shouldn’t be thought of as an “upside to catastrophic warming” — it’s likely that warming of that scale will already have profound and horrible impacts on all facets of life. But if the planet does get to a point where we are desperate enough to try to block out the sun, the tradeoffs to public health need to be considered.

“What keeps me up at night is the possibility we know someone might do this and we’re not planning for it in global health security — entirely uncharted territory where we’re starting from square one on evidence-based decision making,” Carlson said.

The study also shows how some of the ways we think about geoengineering — as a way to reset the world back to a “normal” level — are problematically oversimplified. Blocking out the Sun will involve a whole host of impacts that we don’t yet understand. Geoengineering wouldn’t have a blanket effect on the atmosphere: Carlson said that there’s evidence solar radiation management techniques would have “regional” impacts, potentially changing monsoon patterns or overcooling some areas. And there’s been surprisingly little research, Carlson said, on the public health implications of deploying these kinds of technologies.

“Geoengineering is an active choice to create something new and different than we’ve lived in before, and that includes where malaria risk is,” Carlson said. “For people affected by that choice, I think it matters to be clear about that — because what we’re talking about is a real-world trolley car problem at a planetary scale.”