.ON APRIL 2ND a device looking like a snow device on the deck of the USS Hornet, an invalid aircraft-carrier moored in San Francisco Gulf, started generating a moisture of salty aerosol fragments. The scientific cooperation responsible for the venture, the Marine Cloud Whitening (MCB) program, led due to the University of Washington, is actually exploring whether such sprays could help to slow down weather improvement with a form of "geoengineering". What does this term method-- and why is it so debatable?