A city a quarter of a mile wide, and 3,700+ miles long, that stops the desert.

I said I wasn’t going to do a post on a TED talk, I SWORE I wasn’t going to do a post on a TED talk, I lied. Many of you probably watch TED talks, especially those on Architecture and Design, so you may have seen this. What is this? This.

A man-made sandstone wall/structure/oasis which cuts across the desert.

This is huge.

Here’s the TED talk, which you can watch in lieu of my synopsis http://www.youtube.com/watch?v=PXMJobWlXks

Watch that and you can skip to my response… or not, your call.


The problem, no, wait, opportunity, that is being addressed here is desertification, the addresser is Magnus Larsson, an architectural grad student who proposed this as his thesis. The idea is simple, in much the same way that an iceberg is small.

We begin with the impetus for this project. Desertification.

Simply put the desert moves. Sand in large amounts acts much like a fluid, one which migrates with the wind, and can flow over land. On the southern border of the Sahara, this is a huge problem, because as dunes push south they cover crop and brush land, killing it, and turning it into just more desert. Traditionally this movement was retarded by trees along the edge of the desert, which catch sand and create a barrier which holds the line. The problem is that the trees have been cut down by people living in the area, for firewood, for construction material, for cropland. The reasons for this are complex. The effect is that the desert keeps moving south, pushing people with it, which means one group has to move into the lands of another, and then you get ethnic tension, war, death, suffering, bad things.

One solution to this problem is called Green Wall Africa. It suggests planting a line of trees 4000 miles long to replace those that have been cut down. The problem is that the people who did the cutting are still there, and they still have axes and the need for firewood.

Larsson proposes a different solution, a radical one. Using a bacteria found in swamps, which forms a shell by bonding sand together with calcium carbonate that it secretes, he plans to create a sandstone wall which stretches for the length of the southern end of the desert. The notion is that you inject this bacteria along with the food it needs, into the southernmost sand-dune, by varying the depths of the injections you can create any shape needed within the bounds of the original dune. It is in essence a massive 3D printer. Once the bacteria have created the sandstone, you cease to feed them, and they die. Then you wait. Wind clears out the un-fixed sand and leaves you with a huge structure made entirely out of sandstone.

These spaces would be shaded, and thus could act as condensation chambers, creating pools of water on the edge of the desert, add vegetation and you have a miles long oasis, with living spaces. Local peoples could occupy the space, and not needing wood for construction material, could be induced to tend the trees as a crop, rather than harvesting them as a resource. The sand which blows over the top of the dune would be captured by the trees, and the dune itself would be fixed in place. An elegant, beautiful, and (possibly) practical solution to a major challenge. Why won’t it work?

I watched this talk back when it was posted in 2009, and there was a small flurry of excitement about the project, encouraged by the lovely renders Magnus Larsson provided

Since then I have been looking for the next step, it hasn’t come.

Perhaps it’s simply an idea that has not yet had it’s time, or perhaps there are serious problems with the notion. Larsson’s estimate that the cost would be quite low ($60 initial investment for the bacteria, and then merely ā‰ˆ$11 for each cubic meter, vs ā‰ˆ$90 for each cubic meter of concrete) could be wrong, I have seen neither a refutation of the fact, nor support for it. I think though, that the largest barrier is probably social. The area is poor, unstable, and has a low population, and the idea is grand and complex. Until the richer countries of the world see this problem as their problem, such ideas are likely to remain no more than curiosities, not possible solutions. I would love to see a trial of this though.

Some problems:

Beyond financial, there are many pitfalls a project like this would face. One is that it is geoengineering on a grand scale, and the record of humans trying to fix nature is not very good, and as more and more information emerges on various interventions, our record is getting worse. In some ways however this project is far less unnatural, despite it’s oddity. Sandstone is a natural process, and trees preventing desertification is a natural process, this project therefore is simply mimicking nature to fix a problem caused by humans. Another major problem is that this wall would extend though many different areas which are filled with strife, violence, and poverty, and inhabited by people who either have very little contact with the outside world, or have plenty, and most of it bad. The locals often have a well earned mistrust of westerners and outsiders who come into their lands to put in projects (like say, mines). Working with locals would be key to the success, but that is not always an easy proposition. There are many other challenges, however the downsides of ignoring this problem number in the millions, each one of them an unnecessary death, so at least considering crazy solutions like this is clearly the ethical thing to do.


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