.ON APRIL 2ND a device looking like a snowfall maker on the deck of the USS Hornet, a nonexistent aircraft-carrier moored in San Francisco Gulf, began generating a mist of salty aerosol bits. The medical cooperation behind the project, the Marine Cloud Brightening (MCB) program, led due to the College of Washington, is actually looking into whether such sprays might help to slow down weather modification through a kind of "geoengineering". What performs this term method-- and why is it so controversial?