Greenhouses usually provide warm growing conditions in cooler climates. But why not use the idea in reverse to make growing crops possible in inhospitably hot climates?

That's the idea pioneered by Charlie Paton and engineered by Philip Davies in their elegantly simple green tech Seawater Greenhouse Project.

This "reverse" greenhouse is designed to create an environment that is cool, humid and bright, a reverse of the warming effect of typical cold climate greenhouses. It is for use in desert climates adjacent to seawater. First, you have to find a desert next to the sea, which is not too difficult, actually. Then, this is how this idea works:

1. Seawater cools inside the greenhouse

Facing the prevailing sea wind the entire front wall of the greenhouse is a honeycomb lattice that catches seawater and evaporates it. Seawater trickles down over the lattice, cooling and humidifying the air passing through into the planting area.

2. The heat of the sun is reduced

Sunlight is filtered through a specially constructed roof that only allows visible light through to promote photosynthesis, but trapping the infrared heat in an isolated chamber, reducing at least 30% of the heat.

3. Fresh water is created by condensation

Cool air passes through the planting area and then combines with the hot dry air contained in the roof cavity. The mixture passes through a second sea water evaporator creating extremely hot water-saturated air, which then flows through a condenser cooled by old deep sea water. This extreme temperature difference causes fresh water to condense.

4. Water is reused for irrigation

The freshwater thus created is then stored in a tank underneath the ground where it is kept cool and piped back up to irrigate crops inside the greenhouse, as well as outside under a canopy.

What a beautiful and simple idea.

Continued growth in demand for water and increasing supply shortages are two of the most certain and predictable scenarios of the 21st century. And desertification continues to creep toward ever more people. Agriculture, with its high demand for water, will be a major pressure point.