.ON APRIL 2ND a contraption being similar to a snowfall maker on the deck of the USS Hornet, an obsolete aircraft-carrier moored in San Francisco Gulf, began making a mist of salty spray bits. The clinical cooperation behind the task, the Marine Cloud Whitening (MCB) programme, led due to the University of Washington, is actually examining whether such sprays could aid to slow temperature improvement with a type of "geoengineering". What performs this phrase way-- and why is it thus controversial?