.ON APRIL 2ND a device looking like a snow equipment on the deck of the USS Hornet, an invalid aircraft-carrier anchored in San Francisco Bay, began creating a haze of salty spray particles. The scientific cooperation behind the task, the Marine Cloud Brightening (MCB) program, led due to the College of Washington, is examining whether such sprays may help to reduce climate adjustment through a kind of "geoengineering". What does this condition way-- and why is it therefore debatable?