.ON APRIL 2ND a device appearing like a snowfall equipment on the deck of the USS Hornet, an inoperative aircraft-carrier moored in San Francisco Bay, started generating a haze of salted aerosol fragments. The scientific cooperation behind the job, the Marine Cloud Whitening (MCB) programme, led by the Educational institution of Washington, is checking out whether such aerosols could aid to reduce environment improvement by means of a type of “geoengineering”. What does this condition mean– and also why is it therefore questionable?