As hot air is pumped into the greenhouse, the seawater evaporates, depositing its salts on the cardboard. These strengthen the cardboard, enabling it to last indefinitely. The roof of the greenhouse is double skinned and designed only to let in light in the red and blue spectrums, which are necessary for photosynthesis. Air in the cavity between the two skins is heated by infrared and ultraviolet light, helping to drive the evaporation process. The result is a significant lowering of the temperature in the greenhouse itself.
Air is pumped through the cool greenhouse and through a second evaporator.
This brings it to saturation point. It then passes through a condenser, which is cooled using cold, deep seawater. Pure, distilled water is condensed out and is piped to a storage tank. It can then be used to water the crops in the greenhouse and adjacent shade tent. Any surplus can be used on the land nearby.