A proposed geoengineering strategy to combat climate change by dimming the sun could inadvertently expose airline passengers and crew to hazardous levels of sulfuric acid, according to research. The plan, known as stratospheric aerosol injection (SAI), involves releasing sulfur dioxide gas into the stratosphere, where it would transform into reflective sulfate particles to bounce sunlight back into space.
While the stratosphere is far above the typical flight paths of commercial jets, some proposals suggest using aircraft like Boeing 777s to inject aerosols at higher latitudes where the stratosphere is lower. This approach, however, could place aircraft on routes from North America to Europe and Asia directly in the path of these injections.
Professor Alan Robock, lead author of the study from Rutgers University, explained that commercial airliners process cabin air through their engines. If sulfur dioxide is drawn into this system, it could react to form sulfuric acid. While the acid is corrosive, experts do not believe it would damage the aircraft itself. However, concentrations in some areas could reach up to 50 micrograms per cubic meter, exceeding European Union limits for hazardous substances.
Exposure to sulfuric acid can irritate the throat and lungs, trigger asthma attacks, and potentially lead to more severe respiratory issues or an increased risk of stroke with long-term exposure. This poses a significant health risk for flight crews and frequent flyers on polar routes.
Scientists typically view climate change as an energy imbalance caused by greenhouse gases trapping heat. As emissions continue to rise, some researchers are exploring methods to reduce the amount of solar energy entering the Earth's system. SAI is one such proposed solution, aiming to mimic the cooling effect of large volcanic eruptions.
A study by Columbia Climate School indicated that SAI could disrupt global weather patterns, potentially affecting monsoon systems and sea levels if aerosols are released over polar regions. Modeling suggests that injecting 12 million tons of sulfur dioxide near the equator could cool the planet by 0.6°C to 1°C, helping to stay below the 1.5°C warming threshold outlined in the Paris Agreement.
However, the altitude at which aerosols would need to be injected is a critical concern. Generally, SAI requires injection at 8 to 9 miles (13 to 15 km) above the ground, higher than most commercial flights. The alternative of using aircraft at higher latitudes introduces the risk of airborne exposure.
Some experts, like Dr. Wake Smith, a climate researcher at Harvard University, argue that the risks warrant further study but should not disqualify SAI as a climate mitigation tool. He suggested that cabin air filters could potentially be reconfigured to filter out sulfur dioxide, mitigating the hazard for the public.
Geoengineering encompasses large-scale manipulation of Earth's climate processes to counteract global warming. Other proposed methods include afforestation, artificial ocean upwelling, ocean alkalinization, and ocean iron fertilization, each with its own set of potential drawbacks and scientific uncertainties.