.ON APRIL 2ND a contraption resembling a snowfall maker on the deck of the USS Hornet, an inoperative aircraft-carrier anchored in San Francisco Gulf, started producing a haze of salty aerosol bits. The clinical collaboration behind the job, the Marine Cloud Brightening (MCB) program, led due to the Educational institution of Washington, is actually investigating whether such sprays may assist to reduce temperature adjustment with a kind of "geoengineering". What does this condition method-- and why is it therefore debatable?