.ON APRIL 2ND a device looking like a snow device on the deck of the USS Hornet, an inoperative aircraft-carrier tied in San Francisco Gulf, began making a haze of salty spray particles. The medical cooperation behind the task, the Marine Cloud Brightening (MCB) programme, led due to the Educational institution of Washington, is actually checking out whether such aerosols could help to reduce temperature modification through a kind of "geoengineering". What does this condition method-- and also why is it so debatable?