.ON APRIL 2ND a contraption appearing like a snowfall machine on the deck of the USS Hornet, a nonexistent aircraft-carrier anchored in San Francisco Bay, started producing a moisture of salty aerosol fragments. The clinical cooperation responsible for the venture, the Marine Cloud Whitening (MCB) programme, led due to the University of Washington, is actually exploring whether such aerosols may aid to reduce climate modification via a kind of "geoengineering". What does this term way-- as well as why is it therefore controversial?