.ON APRIL 2ND a gizmo appearing like a snowfall equipment on the deck of the USS Hornet, a defunct aircraft-carrier anchored in San Francisco Bay, began making a moisture of salted aerosol particles. The scientific cooperation behind the job, the Marine Cloud Whitening (MCB) programme, led by the Educational institution of Washington, is checking out whether such sprays might aid to reduce temperature improvement through a type of "geoengineering". What does this phrase way-- as well as why is it therefore controversial?