.ON APRIL 2ND a gizmo being similar to a snowfall device on the deck of the USS Hornet, an invalid aircraft-carrier tied in San Francisco Gulf, started producing a moisture of salty spray fragments. The scientific partnership responsible for the task, the Marine Cloud Brightening (MCB) programme, led by the College of Washington, is checking out whether such aerosols might help to slow down environment modification through a form of “geoengineering”. What does this phrase mean– as well as why is it so controversial?