.ON APRIL 2ND a device resembling a snowfall equipment on the deck of the USS Hornet, an obsolete aircraft-carrier anchored in San Francisco Bay, started making a haze of salted spray particles. The scientific cooperation behind the job, the Marine Cloud Brightening (MCB) program, led due to the Educational institution of Washington, is actually examining whether such aerosols might help to slow weather improvement with a form of "geoengineering". What performs this term method-- and also why is it thus controversial?