.ON APRIL 2ND a contraption looking like a snow equipment on the deck of the USS Hornet, a defunct aircraft-carrier anchored in San Francisco Bay, started producing a mist of salty spray particles. The scientific collaboration responsible for the venture, the Marine Cloud Whitening (MCB) programme, led by the Educational institution of Washington, is actually checking out whether such aerosols may assist to decrease weather change by means of a kind of "geoengineering". What does this condition way-- and also why is it thus controversial?