.ON APRIL 2ND a gizmo resembling a snow machine on the deck of the USS Hornet, an invalid aircraft-carrier tied in San Francisco Gulf, began creating a mist of salted spray fragments. The medical collaboration responsible for the job, the Marine Cloud Brightening (MCB) program, led by the University of Washington, is investigating whether such aerosols could help to reduce climate change by means of a type of “geoengineering”. What performs this term way– and why is it therefore questionable?