.ON APRIL 2ND a device being similar to a snow device on the deck of the USS Hornet, a defunct aircraft-carrier anchored in San Francisco Gulf, began making a haze of salty aerosol bits. The medical collaboration responsible for the task, the Marine Cloud Whitening (MCB) programme, led by the College of Washington, is actually looking into whether such sprays might assist to reduce climate modification through a type of "geoengineering". What does this phrase mean-- and also why is it therefore questionable?