Geoengineering is shorthand for the idea of fixing the problem of man-made climate change once the greenhouse gases that cause it have already been emitted into the atmosphere, rather than trying to stop those emissions happening in the first place. Ideas for such fixes include smogging up the air to reflect more sunlight back into space, sucking in excess carbon dioxide using plants or chemistry, and locking up the glaciers of the world’s ice caps so that they cannot fall into the ocean and cause sea levels to rise. Many people think such ideas immoral, or a distraction from the business of haranguing people to produce less carbon dioxide, or both—and certain to provoke unintended consequences, to boot.