.ON APRIL 2ND a gizmo being similar to a snow machine on the deck of the USS Hornet, a defunct aircraft-carrier moored in San Francisco Bay, started producing a moisture of salted spray particles. The clinical partnership behind the project, the Marine Cloud Whitening (MCB) programme, led due to the Educational institution of Washington, is looking into whether such sprays might assist to slow down climate improvement through a kind of “geoengineering”. What performs this term mean– as well as why is it thus disputable?