.ON APRIL 2ND a device looking like a snow device on the deck of the USS Hornet, a nonexistent aircraft-carrier anchored in San Francisco Gulf, started making a haze of salty spray bits. The scientific cooperation responsible for the job, the Marine Cloud Whitening (MCB) program, led by the University of Washington, is actually looking into whether such sprays might aid to slow climate change via a form of "geoengineering". What does this phrase way-- as well as why is it so debatable?