Scientists have calculated the most effective height for spraying aerosols that can contain global warming. It was previously thought that it was 20 km above sea level. The study is published in the journal Environmental Research Communications.

The new report, commissioned by the US National Academy of Sciences, Engineering and Medicine, is the first official document to contain information on aerosol spraying at an altitude of more than 20 km. From the point of view of economic efficiency, a height of 25 km is considered optimal. This is how geoengineers estimated the maximum height at which aerosols can be sprayed into the atmosphere to reflect incoming sunlight and counteract global warming. However, scientists warn that solar geoengineering can be associated with high economic costs and safety risks.

Wake Smith, lead author of the study, says: “Our finding changes the understanding of how climate intervention models work on a global scale and shows that practical height constraints in developing solar geoengineering programs need to be weighed against radiative efficiency.”

Several notable studies over the past decade have shown that stratospheric aerosol spraying at 25 km would be more efficient than at 20 km, so climate modelers routinely include these altitudes in their studies. For reference, airliners and military aircraft typically fly at an altitude of about 10 km, while 20 km is the area for high-flying spy planes and drones. But performing hundreds of thousands of annual flights to deploy solar geoengineering systems at altitudes beyond the reach of even spy planes would not only substantially increase costs, but also pose unacceptable risks to the safety of flight crews, aircraft, and the uninterested public on Earth.