.ON APRIL 2ND a device appearing like a snow machine on the deck of the USS Hornet, a defunct aircraft-carrier tied in San Francisco Gulf, started generating a haze of salty aerosol fragments. The clinical partnership responsible for the task, the Marine Cloud Brightening (MCB) programme, led due to the Educational institution of Washington, is investigating whether such sprays might assist to decrease weather change via a kind of "geoengineering". What performs this phrase way-- and why is it thus questionable?