.ON APRIL 2ND a contraption resembling a snowfall equipment on the deck of the USS Hornet, an inoperative aircraft-carrier moored in San Francisco Gulf, began making a haze of salty aerosol particles. The scientific cooperation behind the task, the Marine Cloud Whitening (MCB) programme, led by the Educational institution of Washington, is actually examining whether such sprays could assist to slow environment improvement through a form of "geoengineering". What performs this phrase mean-- as well as why is it so controversial?