.ON APRIL 2ND a gizmo being similar to a snow machine on the deck of the USS Hornet, an invalid aircraft-carrier tied in San Francisco Bay, began making a haze of salted spray bits. The medical collaboration responsible for the venture, the Marine Cloud Whitening (MCB) programme, led due to the Educational institution of Washington, is looking into whether such aerosols may assist to decrease weather change by means of a type of "geoengineering". What performs this phrase method-- and why is it so debatable?