July 1998 Newsgroup Discussion

Subject: Let's terraform the Saraha Desert!

Most places on Earth have abundant life, and it'd be a shame to destroy such ecosystems, even most deserts. But there's one desert that has such a small amount of life that I think we should make the effort to "terraform" it: the Sahara.

I propose that we first use radar etc. to do all the examinations of ancient things under the sand that we'll ever want to do, then begin adding water and removing sand to make the Sahara more hospitable to a wide range of life. We may lose a few desert species, but we'll make room for many thousands of other species to survive in the terraformed Sahara when they would have otherwise gone extinct.

It's currently too hot for people to live comfortably in the Sahara, so during the initial states of terraforming I propose that we use remote control such as telepresence. We'll have to use high-temperature semiconductors, which are more expensive than regular semiconductors, but they are far less expensive than setting up lots of air-conditionned habitats for on-site humans. We already have satellite telecommunications available to link the on-site robots with their controllers nearly anywhere on Earth.

I propose that we start to build infrastructure to lift seawater (from the Mediterranean, or from the Atlantic, depending on logistics and politics) and spray it on the sand near where the prevailing winds are entering the desert. With enough water evaporating from a single local vicinity, as the steam rises it'll form clouds, which will shade the down-wind part of the desert and thereby cool it. Sunlight could be focussed to heat sand enough to make it fuse together (or actually melt), to consume sand at the same time as manufacturing crude canals for transporting water from one place to another. To move water uphill, first lift it using a solar-powered archimedes helix, then let it flow slightly downhill along a fused-sand canal to the next archimedes helix pump. (To do the excavation necessary that the canal is sloped opposite to the general land, it's probably easier to dig away sand from under the up-hill end of the canal, rather than try to prop the down-hill end up above the ground.)

Once we get a few pumping stations chained, so that saltwater is being pumped several miles into the desert, we can start growing saltwater life in fused-sand ponds. Miagrating birds will be attracted to the new food supply, dropping fertilizer for free.

Given the worldwide remote-control network, we could hire our own unemployed people (including disabled), and aliens we'd otherwise give humanitarian aid to, and of course we'd hire people of the countries where the work is being done and the land is being modified. The infrastructure we'd develop would later prove useful when we start setting up habitat on the Moon and/or terraforming Mars.

"Robert Maas" wrote:

(quote)It's currently too hot for people to live comfortably in the Sahara, so during the initial states of terraforming I propose that we use remote control such as telepresence.

I like the general idea of transforming the Sahara; it would be a boon for the countries which have lost most of their arable land to this growing desert, and it'd be great experience in large-scale ecological engineering. But I think using telepresence for this is a bit silly; people can live in the desert just fine. Tents, sunblock, and lots of fans. They've been doing it for years.

(quote)I propose that we start to build infrastructure to lift seawater (from the Mediterranean, or from the Atlantic, depending on logistics and politics) and spray it on the sand near where the prevailing winds are entering the desert. With enough water evaporating from a single local vicinity, as the steam rises it'll form clouds, which will shade the down-wind part of the desert and thereby cool it.

It'd be interesting to see some climate modeling, to tell us whether such a thing might actually happen.

Anyway, I did a Yahoo/AltaVista search and turned up surprisingly little info on the Sahara (but see [1]). If you're serious about pushing this idea, a good start would be to set up a web site on this desert, and post all the information you can find. Then you can add links to climate modeling resources, get some ecologists and engineers involved, etc.

[1] Advice on crossing the desert: http://www.eden-foundation.org/sahara/

(quote) the Mediterranean, or from the Atlantic, depending on logistics and politics) and spray it on the sand near where the prevailing winds are entering the desert. With enough water evaporating from a single local vicinity, as the steam rises it'll form clouds, which will shade the down-wind part of the desert and thereby cool it.

I've taken a look at mean wind maps for the Sahara, and there are several reasons why this won't work. First, there's a large high-pressure system over the Sahara: the prevailing winds generally blow clockwise *around* and *away* from the desert, rather than toward it. This is accompanied by a large-scale sinking of very dry air from high in the atmosphere; this air is warmed by adiabatic compression as it sinks. This is the whole reason the Sahara is there in the first place.

This means that there isn't anyplace you could pour seawater on the sand and have it generate clouds over the Sahara: the moist air would blow offshore. Even if you could dump it in the exact center of the desert, clouds are typically formed by *rising* air-masses. The air over the Sahara is generally *sinking*: you'd end up with humid air, but no clouds or rain.

You'll notice that there is a large desert belt stretching clear around the globe near latitudes 25 North and 25 South; this is the transition zone between the eastward-equatorward blowing tradewinds and the poleward-westward blowing Westerlies, and is a region of diverging winds and descending air. You can't change the Sahara unless you change the general circulation of the whole planet.

Second, suppose that the prevailing winds did blow onshore (and they do, in a few limited places like Libya). Evaporation rate is strongly controlled by the rate at which solar energy is absorbed by the surface (and thus heated). The oceans have lower albedo (are much darker) than the desert, and therefore absorb *more* energy than the land. They also have moisture more readily available at the surface (evaporation over land slows dramatically after the top few millimeters becomes dry). So evaporation over the ocean is actually *much more* than over land -- so you won't add evaporation by pumping seawater onto the land, even if you were able to flood a land area the size of the Mediterranean. (I've ignored the fact that the land is hotter than the sea --- but the main reason it's hotter is that it isn't cooled by evaporation!)

Second, I'll remind you of the old story that soldiers used to sow the ground of their enemies' farmland with salt: this ensured that nothing would grow there. When you pump seawater onto the desert, it'll leave the salt behind as it evaporates, forming a giant salt flat -- which will be much more 'deserted' than the Sahara already is.

Third, you seem to believe that the Sahara is a giant field of sand dunes. It isn't. There are several "dune seas", but also large areas of flat pebbly land, and other areas with "dirt", small shrubs and grasses, and other areas with rather big mountain ranges and bouldery hills.

Essentially, your plan would transform a viable but marginal ecosystem into a sterile salt-flat wasteland, even if you could achieve it.

Oh, one last note: The difference in rainfall and evaporation per year between a temperate place like the U.S. and a dry place like the Sahara is equal to a column of water one meter deep over the entire area. The Sahara has a surface area of 10 million square kilometers, so even if the winds were right (and they aren't), you need to supply 300,000 cubic meters of water per second. This is twice the outflow of the Amazon river. The water will leave behind 350 million tonnes of salt; if distributed evenly over the Sahara, that's 1 centimeter of built-up salt per year.

Jason Goodman
Graduate Student
MIT Program in Atmospheres, Oceans, and Climate

(quote)twice the outflow of the Amazon river. The water will leave behind 350 million tonnes of salt; if distributed evenly over the Sahara, that's 1 centimeter of built-up salt per year.

What could be done is lots of netting that catches the humid air as dew in the morning.

This precious water could then be fed into transparent hose to grow algae. The algae can then be pumped to a water reuseing greenhouse where the suns heat drys it and the evaporate is collected. The algae can be fed to various creatures such as mushrooms or snails even, to make it more edible for the table.

If it had to be cooled, then a tank of water, underground, could be pumped through hose, under the cool night sky and then it could be a resovoir during the day. Or it could be allowd to evaporate somewhere in the flow circuit, thus cooling it and the vapour could go into a compressor that is air cooled and turned back to water.

Of course the whole lot could be automatic and solar powerd. Just needs investment and a market demand.

John Biosicfix www.nine7.demon.co.uk Lots of links
*****Us neurons dont know very much, this is a sure thing****
If it's not on fire, it's a software problem.

(quote)You'll notice that there is a large desert belt stretching clear around the globe near latitudes 25 North and 25 South; this is the transition zone between the eastward-equatorward blowing tradewinds and the poleward-westward blowing Westerlies, and is a region of diverging winds and descending air. You can't change the Sahara unless you change the general circulation of the whole planet.

Interesting idea. I am intrigued by the Saharan rock paintings which depict a land teeming with wildlife, like what is now East Africa. If the processes were better understood that transformed that lush land into today's desert, it just may be that the general circulation of the entire planet could be changed. As to whether it SHOULD be, that is another question. The results would be unprdictable with our present state of knowledge.

(quote) There are several "dune seas", but also large areas of flat pebbly land, and other areas with "dirt", small shrubs and grasses, and other areas with rather big mountain ranges and bouldery hills.

The big mountain ranges would be a good place to begin. As air rises over a mountain range, it cools, and the water vapor condenses. This we can see in the southwestern United States: there are flat deserts with cacti, sagebrush, etc., interrupted by mountains with conifer forests. If a source of moisture could be provided, and the winds did indeed blow across the mountains, I can envision green refugia forming in the Ahaggar and Tibesti regions, streams flowing down the slopes to the flat country. Unfortinately, unless these streams had outlets, they woud create salt lakes where they reached the flat land; but dependfing on the extent of these salt lakes, they might not be such a problem--and might be the source of water vapor to fuel the hydrologic cycle of the region.

Remember the scene from Star Wars where R2-D2 and C-3PO are on a desert planet? 3PO stikes our across the dunes, while R2 heads for a mountain range. 3PO asks, "what makes you think there are selltlements over there?" and, after R2 replies, objects "don't get technical with me." Apparently, R2 had given a good answer. There is good science to be found in science fiction, if one knows how to find it.

+++++++++++++++++++++++++++++++++++++++++++++++++
Jason Hernandez
freelance researcher

Have you looked in Darwin's black box lately?

(quote)Interesting idea, but i doubt it would ever really get off the ground because nobody would want to fund something that wouldn't directly help them. This is because they wouldn't uderstand that the practice would be very valuable for Mars, etc.

Just a couple of points, as I have thought a bit about this in the past. First, one major benefit of worldwide impact, is that the Sahara is an excellent sink for moisture, which will be handy to forstall sealevel rise as a result of global warming. Naturally, this would only be of significant impact once the climate of the region had altered massively, which will in all probability be too late to prevent some flooding of lowland areas, if a) global warming prceeds as seriously as some predict, and b) no efforts of unprecedented scale are undertaken to green the Sahara at breakneck speed.

Second, a lo-tech process for desalinating water passively using solar heat, with cheap collectors for the evaporate using local materials, could be developed. I envision a system which can evolve naturally, providing a more fertile habitat, which can march inland from the coast, slowly.

Thirdly, one of the benefits of large reflector arrays for solar thermal electric generators, is they shade the ground, reducing evaporation. I can imagine fields developed which do double duty as solar electric generators and cropland. Delivery of water by drip directly to plant roots, as someone mentioned, allows for very efficient use of scarce water.

I believe this is something which will happen, it's just a matter of how fast, and how extensively.

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vincent@triumf.ca <== faster % Pete Vincent
vincent@vcn.bc.ca (freenet) % Disclaimer: all I know I
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