Theoretical super-weapon?

I'm looking for a fictional weapon based on either theoretical or hypothetical science in the real world. The weapon is for a story I'm writing and has to raise a large body of ocean water (I believe one website said 30 square miles, but I need enough to take down the ozone layer so 200-300 square miles) to an excess of 120 degree Fahrenheit (thus creating conditions capable of producing a hypercane)