.ON APRIL 2ND a device looking like a snowfall machine on the deck of the USS Hornet, an inoperative aircraft-carrier moored in San Francisco Gulf, started generating a moisture of salty spray bits. The clinical cooperation behind the venture, the Marine Cloud Brightening (MCB) programme, led by the Educational institution of Washington, is actually checking out whether such aerosols might aid to reduce weather modification through a type of "geoengineering". What performs this term method-- and why is it therefore disputable?