.ON APRIL 2ND a gizmo looking like a snow equipment on the deck of the USS Hornet, an obsolete aircraft-carrier tied in San Francisco Gulf, started making a haze of salty aerosol particles. The clinical partnership responsible for the project, the Marine Cloud Brightening (MCB) program, led due to the Educational institution of Washington, is examining whether such sprays might help to decrease temperature improvement with a kind of "geoengineering". What performs this condition mean-- and why is it so controversial?