‘Solar Geoengineering’ Could Make Malaria Even Worse – The Atlantic

Source: ‘Solar Geoengineering’ Could Make Malaria Even Worse – The Atlantic

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…malaria does not have a linear relationship with temperature. The malaria parasite is spread by mosquitoes, which are cold-blooded and depend on the ambient air temperature to set the pace of their metabolism; malaria risk, then, tends to increase as the temperature gets hotter. It peaks at an average of 25 degrees Celsius, or 77 degrees Fahrenheit, Colin Carlson, a Georgetown University professor and co-author of the paper, told me. But as the temperature keeps rising, mosquitoes become less and less able to function, and at about 34 degrees Celsius, or 93 degrees Fahrenheit, they start “dropping out of the air.” That means there is a hard thermal peak to mosquito survival and, with it, malaria transmission.

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 took a place that would have been too hot to allow mosquito survival and brought it back into a survivable range. In others, it restored the close-to-25-degree-Celsius temperatures that mosquitoes need to thrive.

Of course, mosquitoes are not the only animals that struggle to cope with extreme heat. Humans do too. If it’s so hot out that people and animals cannot survive, then geoengineering may make sense anyway. But the reality is likely to be far more nuanced. “I think it’s a gamble to say that when you add up the catastrophic biological risk [of high temperatures], what you have is not outweighed by other factors,” Carlson said.

One of those other factors might be meningitis, a dangerous and sometimes fatal infection of the tissue surrounding the brain and spinal cord. Because tiny particles of dust can increase the risk of meningitis, the disease is most prevalent in a swath of Africa called the Meningitis Belt, where people are regularly exposed to airborne sand and dust from the Sahara. Seasonal monsoons often rinse the dust out of the air. But in some simulations of geoengineering, the monsoon season weakens, Carlson said, exposing more people in sub-Saharan Africa to dust, and thus perhaps increasing their meningitis risk.

Even if geoengineering reshuffles the geography of malaria while not boosting the overall numbers, increasing transmission in new areas but extinguishing it in the old, that would create a public-health problem. Certain parts of the world have prepared their health and medical infrastructure for malaria; if the burden of the disease shifts to new places, those places won’t have the same built-up expertise and institutional factors designed for it. The disease will exact a higher toll, at least at the beginning.

Keith, the Harvard professor, who has called geoengineering the “least worst” way to cool the planet, told me that this study—and the broader effort it represented to quantify the health impacts of warming—was worthwhile. But he doubted that the math would come out against geoengineering. “It’s good [that] people are looking at it,” he said. “But we shouldn’t be at all surprised that solar geoengineering doesn’t uniformly improve health outcomes, because warming doesn’t uniformly harm health outcomes.” He did a little mental math: The raw destructive power of heat is expected to cause about 5 million deaths a year by the end of the century, he said. Malaria, by comparison, causes about half a million deaths a year, a number that has fallen since the turn of the century. Malaria has a lot of room to get worse before it rivals heat’s end-of-century burden.

More broadly, the study shows that solar geoengineering could worsen people’s lives even in the poor countries that it is supposed to help most. “What vexes me about geoengineering trade-offs is that they’re discussed as if there is one thing called ‘the global South’ that is on the front lines of climate change and that will benefit from ‘solutions,’” Carlson said. “This is the first trolley problem we’ve seen” in studying climate change’s impacts, he said. “There are winners and losers of this.”