The ocean absorbs a great deal of sunlight. There are two ways it balances this heat input: by infrared radiation to space, and by evaporation, which is driven by the thermodynamic disequilibrium between the ocean and atmosphere. Putting greenhouse gases into the atmosphere decreases the amount of infrared radiation that can escape to space, so to compensate, the thermodynamic disequilibrium must increase. It is this disequilibrium that powers hurricanes, so their intensity also increases.