.ON APRIL 2ND a device appearing like a snowfall machine on the deck of the USS Hornet, an inoperative aircraft-carrier anchored in San Francisco Gulf, began producing a mist of salted spray bits. The scientific collaboration responsible for the task, the Marine Cloud Brightening (MCB) program, led due to the College of Washington, is actually investigating whether such sprays could help to slow weather modification through a type of “geoengineering”. What performs this term method– and why is it thus controversial?