.ON APRIL 2ND a device looking like a snowfall device on the deck of the USS Hornet, a defunct aircraft-carrier anchored in San Francisco Gulf, began creating a haze of salty spray fragments. The medical partnership behind the venture, the Marine Cloud Whitening (MCB) programme, led by the College of Washington, is actually investigating whether such aerosols might assist to decrease temperature improvement by means of a kind of "geoengineering". What does this term method-- and why is it thus questionable?