.ON APRIL 2ND a contraption looking like a snowfall machine on the deck of the USS Hornet, an obsolete aircraft-carrier tied in San Francisco Bay, started producing a mist of salted aerosol fragments. The scientific collaboration responsible for the task, the Marine Cloud Whitening (MCB) program, led due to the Educational institution of Washington, is actually looking into whether such sprays might assist to slow temperature improvement with a type of “geoengineering”. What performs this phrase way– and why is it so debatable?