.ON APRIL 2ND a contraption appearing like a snowfall equipment on the deck of the USS Hornet, an obsolete aircraft-carrier anchored in San Francisco Bay, began creating a mist of salted aerosol bits. The medical partnership behind the venture, the Marine Cloud Brightening (MCB) program, led due to the Educational institution of Washington, is checking out whether such sprays might assist to reduce climate improvement via a kind of "geoengineering". What does this phrase mean-- as well as why is it thus controversial?