.ON APRIL 2ND a gizmo looking like a snowfall device on the deck of the USS Hornet, an inoperative aircraft-carrier tied in San Francisco Bay, started generating a mist of salty aerosol bits. The medical collaboration behind the project, the Marine Cloud Whitening (MCB) program, led due to the University of Washington, is actually exploring whether such aerosols might assist to decrease temperature change by means of a form of "geoengineering". What does this term mean-- as well as why is it thus debatable?