.ON APRIL 2ND a gizmo resembling a snowfall equipment on the deck of the USS Hornet, an inoperative aircraft-carrier anchored in San Francisco Bay, began generating a moisture of salty aerosol bits. The medical partnership behind the task, the Marine Cloud Whitening (MCB) program, led by the College of Washington, is exploring whether such aerosols may help to decrease environment adjustment by means of a kind of “geoengineering”. What does this phrase mean– and also why is it thus controversial?