.ON APRIL 2ND a gizmo being similar to a snowfall machine on the deck of the USS Hornet, an obsolete aircraft-carrier anchored in San Francisco Bay, began making a haze of salty aerosol fragments. The clinical collaboration responsible for the task, the Marine Cloud Whitening (MCB) program, led due to the College of Washington, is actually examining whether such aerosols might aid to slow down temperature adjustment with a type of “geoengineering”. What does this term way– and why is it so debatable?