.ON APRIL 2ND a device appearing like a snowfall machine on the deck of the USS Hornet, an inoperative aircraft-carrier moored in San Francisco Gulf, began generating a haze of salted spray particles. The scientific cooperation behind the project, the Marine Cloud Brightening (MCB) programme, led by the University of Washington, is actually looking into whether such sprays might aid to reduce temperature improvement by means of a kind of “geoengineering”. What does this condition method– and also why is it thus disputable?