Armand Neukermans, an engineer, at the Aqua Metrology Systems lab, where his team began work on a sea salt aerosol spraying device, in Sunnyvale, Calif., on March 29, 2024. Brightening clouds is one of several ideas to push solar energy back into space -- sometimes called solar radiation modification, solar geoengineering, or climate intervention. (Ian C. Bates/The New York Times)