My impression is that they take in ocean water that then evaporates as the source of water. This means a very stable humidity, in addition to stable temperature

My impression is that they take in ocean water that then evaporates as the source of water. This means a very stable humidity, in addition to stable temperature, essentially for free. Also, the oceans absorb most of the CO2 emitted by various processes, so if you evaporate it I would guess it comes back out into the air.