.ON APRIL 2ND a gizmo looking like a snow equipment on the deck of the USS Hornet, an inoperative aircraft-carrier anchored in San Francisco Gulf, began producing a moisture of salted aerosol fragments. The scientific cooperation behind the job, the Marine Cloud Brightening (MCB) program, led by the University of Washington, is actually exploring whether such aerosols may aid to decrease weather adjustment with a form of "geoengineering". What does this term method-- and why is it so controversial?