.ON APRIL 2ND a gizmo appearing like a snowfall machine on the deck of the USS Hornet, an obsolete aircraft-carrier tied in San Francisco Bay, started generating a moisture of salted spray particles. The clinical collaboration behind the task, the Marine Cloud Brightening (MCB) programme, led due to the Educational institution of Washington, is checking out whether such aerosols might help to decrease climate improvement through a type of “geoengineering”. What does this term method– and also why is it therefore questionable?