But how do you move the wet waste from London to Mediterranean and Sahara. Also soil is one part of equation. Water is another. Poor soil results in poor vegetation that leads to poor rainfall and water sources. So soil also needs to be coupled with water increase. I think preservation is probably more feasible than rejuvenation. India for example is losing top soil at unprecedented rates that can have devastating consequences.

Start making it in Egypt or Tripoli?

People in deserts shit too, I think.

Well people have been shitting in the desert for centuries, but there’s no jungle yet, so something appears to be missing.

And people have spent millennia over-extracting plants, leading to erosion and desertification and subsequent changes of local weather patterns (precipitation, humidity, etc).

If they'd known to replenish and make broader use of their defecations and organic waste, they might well have kept their 'jungle'.

Certainly, it appears to have worked for ancient Amazonian tribes who are thought to be responsible for much of the quality land in the Amazon basin, much of which would otherwise be quite shallow and sandy with low nutrients.