.ON APRIL 2ND a contraption looking like a snow equipment on the deck of the USS Hornet, a nonexistent aircraft-carrier tied in San Francisco Bay, started producing a mist of salted aerosol bits. The scientific cooperation behind the job, the Marine Cloud Brightening (MCB) program, led by the College of Washington, is actually looking into whether such sprays might assist to slow down weather change with a type of "geoengineering". What does this phrase method-- and also why is it thus controversial?