.ON APRIL 2ND a gizmo looking like a snow machine on the deck of the USS Hornet, an obsolete aircraft-carrier tied in San Francisco Gulf, started producing a haze of salted spray particles. The clinical collaboration responsible for the project, the Marine Cloud Whitening (MCB) program, led due to the College of Washington, is actually checking out whether such aerosols may assist to slow down temperature change through a kind of "geoengineering". What performs this term mean-- and why is it therefore debatable?