.ON APRIL 2ND a device appearing like a snowfall maker on the deck of the USS Hornet, an obsolete aircraft-carrier tied in San Francisco Bay, began making a mist of salted spray particles. The clinical partnership responsible for the task, the Marine Cloud Brightening (MCB) programme, led by the Educational institution of Washington, is actually exploring whether such aerosols may aid to slow environment improvement by means of a kind of "geoengineering". What performs this term way-- and also why is it therefore disputable?