In 1991, Mount Pinatubo erupted in the Philippines, pumping nearly 20 million tons of sulfur dioxide into the sky. This sudden burst of gas in the atmosphere reflected sunlight from Earth and lowered the planet’s average temperature by about 1 degree Fahrenheit for just over a year. If humanity wants to fend off the worst effects of global warming, then it simply has to do that, with planes, indefinitely.
At least that’s the idea of solar geoengineering. For its proponents, mimicking a large volcanic eruption is an ethical necessity, a way to cushion the blow of climate change. “Perhaps the best reason to take cooling seriously is that the benefits seem likely to flow to poorer countries,” wrote David Keith, a professor of applied physics at Harvard. The New York Times Last year. “Poor people tend to live in hot places.”
The technology needed for geoengineering has never been successfully demonstrated, but already many economists are confident that it will happen at some point in this century. That’s because its theoretical costs are little more than a few flights, a spraying device and a few million tons of sulfuric acid – expensive, sure, but not beyond the reach of your average island nation or a money-conscious billionaire. climate.
But geoengineering is far from a safe bet. To his detractorstechnology risks recreating some of the worst mass extinctions in the history of the planet, which were the consequence of the increase both the level of carbon dioxide in the atmosphere and its sulphate level. We are already pumping CO2 in the sky, they argue. Why are we so sure that adding sulfates won’t backfire?
A new study suggests that solar geoengineering is going to be even more complicated than its proponents think: it could expose tens or even hundreds of millions of people to malaria each year. “There is a lot of research on the potential of geoengineering to reduce risks, such as extreme heat and sea level rise,” said Christopher Trisos, study co-author and director of the Climate Risk Lab at the University of Cape Town. in South Africa, told me. “But you can’t just assume that geoengineering universally reduces risk for people.”
In an extreme, worst-case scenario, in which humanity raises global temperatures by several degrees by 2070 before trying to bring them down to 2020 levels, geoengineering could expose perhaps 1 billion people at increased risk of malaria. The study found that geoengineering can reshape major hazards around the world, even in less extreme scenarios. In a more moderate simulation, where humanity achieves net zero carbon pollution by mid-century but still seeks to restore temperatures to 2020 levels, the tricky questions remain. In this world, West African countries like Nigeria and Ghana would see increased risk of malaria for approximately 100 million people in total. But in East African countries, like Ethiopia and Kenya, geoengineering reduce risk of malaria for about 100 million people.
Many scientists fear that climate change will worsen the spread of certain mosquito-borne diseases, such as dengue fever and yellow fever. But malaria is in a category of its own. In 2020, more than 627,000 people died from malaria and some 241 million people contracted it. Malaria remains the sixth leading cause of death in low-income countries, where it kills more people than car accidents, HIV/AIDS and tuberculosis. In the words of the study authors, no other mosquito-borne virus has a toll even “remotely comparable” to the illnesses and deaths caused by malaria.
The trade-off between geoengineering and malaria emerges for two reasons. First, solar geoengineering does not perfectly wind up the Earth’s climate clock. Even if you add enough sulfate aerosols to perfectly counter warming from carbon pollution, you’re still changing the physics of climate, not restoring what once was. Many geoengineering simulations produce strange phenomena, such as “tropical supercooling”, in which land near the equator is colder than expected, even though land near the poles remains much warmer. The most recent reports from the Intergovernmental Panel on Climate Change found that these regional and seasonal distortions appear “with great confidence” in many types of geoengineering models.
And that’s a problem, because malaria doesn’t have a linear relationship with temperature. The malaria parasite is spread by mosquitoes, which are cold-blooded and depend on ambient air temperature to regulate their metabolic rate; the risk of malaria therefore tends to increase as the temperature rises. It peaks at an average of 25 degrees Celsius, or 77 degrees Fahrenheit, Colin Carlson, a professor at Georgetown University and co-author of the paper, told me. But as the temperature continues to rise, the mosquitoes become less and less able to function, and at around 34 degrees Celsius, or 93 degrees Fahrenheit, they begin to “drop from the air.” This means that there is a thermal peak that is difficult for mosquitoes to survive and, with it, for the transmission of malaria.
The study found that tropical overcooling and the ideal temperature for malaria transmission can interact in troubling ways. In some parts of the world, geoengineering has taken a location that would have been too hot for mosquitoes to survive and brought it back into a survival range. In others, it has restored the near 25 degrees Celsius temperatures that mosquitoes need to thrive.
Of course, mosquitoes aren’t the only animals struggling to cope with the extreme heat. Humans too. If it’s so hot that people and animals can’t survive, then geoengineering might make sense anyway. But the reality is likely to be much more nuanced. “I think it’s a bet to say that when you add up the catastrophic biohazard [of high temperatures]what you have is not outweighed by other factors,” Carlson said.
One of these other factors could be meningitis, a dangerous and sometimes fatal infection of the tissues surrounding the brain and spinal cord. Because tiny dust particles can increase the risk of meningitis, the disease is most prevalent in a part of Africa called the meningitis belt, where people are regularly exposed to airborne sand and dust in the air. Saharan air. Seasonal monsoons often push dust out of the air. But in some geoengineering simulations, the monsoon season weakens, Carlson said, exposing more people in sub-Saharan Africa to dust, and thus possibly increasing their risk of meningitis.
Even if geoengineering reshapes the geography of malaria without increasing the overall numbers, increasing transmission in new areas but extinguishing it in old ones, it would create a public health problem. Some parts of the world have prepared their health and medical infrastructure for malaria; if the disease burden shifts to new places, those places will not have the same accumulated expertise and institutional factors designed for it. The disease will exact a higher toll, at least initially.
Keith, the Harvard professor who called geoengineering the “least worst” way to cool the planet, told me that this study – and the broader effort it represented to quantify the impacts of warming on the health – was worth it. But he doubted that mathematics would oppose geoengineering. “It’s good [that] people watch it,” he said. “But we shouldn’t be at all surprised that solar geoengineering doesn’t uniformly improve health outcomes, because warming up does not uniformly impair health outcomes. He did a little mental math: The raw destructive power of heat is expected to cause around 5 million deaths a year by the end of the century, he said. Malaria, by comparison, causes around half a million deaths a year, a number that has been declining since the turn of the century. Malaria has plenty of room to get worse before it rivals the burden of the turn-of-the-century heat.
More broadly, the study shows that solar geoengineering could make people’s lives worse even in the poor countries it’s supposed to help the most. “What vexes me about geoengineering trade-offs is that they’re being discussed as if there’s a thing called ‘the global South’ that is on the frontlines of climate change and will benefit from ‘solutions’. ‘” Carlson said. “This is the first cart problem we’ve seen” in studying the impacts of climate change, he said. “There are winners and losers.”