.ON APRIL 2ND a device being similar to a snowfall maker on the deck of the USS Hornet, a defunct aircraft-carrier tied in San Francisco Bay, began producing a haze of salted aerosol bits. The medical cooperation behind the job, the Marine Cloud Brightening (MCB) program, led due to the University of Washington, is examining whether such sprays might assist to reduce weather improvement with a form of "geoengineering". What does this condition way-- and also why is it so controversial?