[datenwolf]

> irrigating deserts profitable

Irrigating deserts doesn't really work that well. The main problem is, that undistilled water always contains some ions, i.e. salts (it's got electrolytes!). If the main process for loss of water is evaporation these salts are left behind leading to salinization. You don't really want that.

If you want to fight desertification, then you must combat evaporation first, which you'd do for example with engineering the soil. Only after you've figured out how to make the soil keep the water, then you may start to thing about irrigation.

[mywittyname]

> If you want to fight desertification, then you must combat evaporation first,

This is something plants can be remarkably good at!

I don't think you can get around irrigation to bootstrap the process. We could probably begin the process by putting down some irrigated top soil, and laying a bio-degradable, transparent moisture barrier to keep the water from evaporating while the ground cover grows.

Alternatively, I'm sure we could construct a man-made river running through a desert to revitalize it. I'm not a geologist, but I suspect that the existence of an active river is a strong influence on whether a region becomes a rain forest or a desert.