.ON APRIL 2ND a gizmo appearing like a snow machine on the deck of the USS Hornet, an obsolete aircraft-carrier tied in San Francisco Gulf, started creating a mist of salty aerosol fragments. The clinical collaboration behind the task, the Marine Cloud Whitening (MCB) program, led due to the University of Washington, is actually examining whether such sprays might aid to reduce temperature improvement with a kind of "geoengineering". What does this phrase way-- and why is it thus controversial?