.ON APRIL 2ND a gizmo resembling a snowfall machine on the deck of the USS Hornet, a defunct aircraft-carrier moored in San Francisco Bay, started making a moisture of salted spray bits. The scientific partnership behind the venture, the Marine Cloud Brightening (MCB) program, led due to the Educational institution of Washington, is investigating whether such aerosols may assist to decrease temperature improvement through a kind of "geoengineering". What does this term mean-- and also why is it thus questionable?