.ON APRIL 2ND a device looking like a snow machine on the deck of the USS Hornet, a defunct aircraft-carrier anchored in San Francisco Gulf, began making a haze of salty aerosol bits. The scientific collaboration responsible for the project, the Marine Cloud Brightening (MCB) program, led by the College of Washington, is looking into whether such aerosols may aid to decrease weather modification via a kind of "geoengineering". What does this condition method-- and also why is it therefore disputable?