The other geoengineering idea, solar radiation management (SRM), envisions cooling Earth by putting mirrors in space, pumping salt spray from ships into clouds to make them brighter, or filling the stratosphere with a sulfuric acid cloud, just as volcanic eruptions occasionally do. But volcanic eruptions teach us that, while a cloud in the stratosphere would indeed cool the planet and stop ice from melting and the sea from rising, it would also destroy ozone and produce regional droughts.