.ON APRIL 2ND a device appearing like a snowfall device on the deck of the USS Hornet, a defunct aircraft-carrier anchored in San Francisco Bay, started creating a haze of salted spray particles. The medical collaboration responsible for the venture, the Marine Cloud Whitening (MCB) program, led due to the University of Washington, is exploring whether such sprays might aid to slow down weather adjustment via a type of "geoengineering". What performs this phrase mean-- and why is it therefore debatable?