.ON APRIL 2ND a gizmo looking like a snowfall maker on the deck of the USS Hornet, a nonexistent aircraft-carrier tied in San Francisco Gulf, started generating a haze of salty aerosol fragments. The medical collaboration behind the job, the Marine Cloud Brightening (MCB) programme, led by the University of Washington, is exploring whether such sprays could help to reduce temperature improvement via a form of "geoengineering". What performs this phrase way-- and also why is it thus questionable?