.ON APRIL 2ND a device being similar to a snow equipment on the deck of the USS Hornet, a nonexistent aircraft-carrier moored in San Francisco Gulf, started producing a haze of salted spray bits. The clinical cooperation behind the task, the Marine Cloud Whitening (MCB) programme, led by the Educational institution of Washington, is looking into whether such aerosols could aid to slow climate change through a form of "geoengineering". What performs this condition method-- and why is it therefore controversial?