Greening a desert. Would this be worth a try?

[sethoflagos]

On 8/30/2022 at 9:18 PM, mistermack said:

I don't find your responses particularly informed or useful. Others have posted cogent posts, but yours are becoming rude, and certainly not worth reading. Byeeee.

I presume the near simultaneous disappearance of 2 reputation points from my posts on this topic, and your reappearance on this site are not unconnected events.

Just to be clear. None of negative reps you received for the quoted post came from me. They are the result of how others perceived your behaviour.  

[Lady of Elms]

On 8/16/2022 at 10:55 AM, mistermack said:

I've dreampt up a speculative scheme for greening a desert. Do you think it would work? (or be cost effective?)

You need a desert that extends right up to a significant sea or the ocean. Like lots of Australia, or Namibia etc. Australia would be the best to try it on. 

Imagine you set up a huge array of pumps along, for example, the Great Australian Bight. Connect the pumps to spray nozzles, and start pumping when there is an onshore wind. Adjust the jets for a spray that evaporates most of the water, before it falls back into the ocean. So basically, you are manufacturing water vapour, from sea water, with the salty residue falling back into the ocean. 

So with an onshore wind, all of that humid air is carried inland, where it rises on thermals, forms clouds and rain, greening the land. If the wind blows the other way, you switch it off. 

Obviously, it could only be done on a national level, so that the benfits could be taxed and provide financing for the running of the system. 

Besides providing land that could now be used for agriculture, it could raise the level and quality of groundwater, cool the climate with more cloud cover, and actually get rivers flowing and lakes filling. 

If it worked. Any thoughts?

I've got some background in environmental sciences, and the very first thing you need to "green" anything is water retention and stable substrate. Shifting ground and water evaporation will greatly impede and plants trying to grow in an area.  An oasis is a place where there is a large collection of protected water thanks to local geological structures. They're usually natural springs or wells from the water table below the desert sand. Plants require a place to root and annually reliable soil. Simply watering the sand isn't going to be enough. 

Wind erosion is also a major hurdle for plants. Some can withstand flat, open lands with full sun and arid temperatures, but not the kind that will create a forest. The Dust Bowl in the United States was a good example of this. Rich soil is created by lots of organic matter. The best way to create more forest against a desert is to start on the edge and keep building ecologically sustainable areas inwards. That might mean digging wells or creating large ponds and lakes to hold what little rainfall there may be.  I know there are people that use something called 'swales' to do this. 

https://naturalbuildingblog.com/greening-us-deserts-80-year-old-swales-near-tucson-arizona/ 

If you want to create a lasting forest, it has to be able to survive after the initial human intervention. There are a lot of other factors, too, such as which plants to grow in that area (you want hardy, native, 'foundation' species to begin), but you definitely want to work with nature rather than against it. 

[paulsutton]

On 8/16/2022 at 4:07 PM, exchemist said:

I think one difficulty would be that the salt would not drop back into the ocean. As each droplet progressively evaporated and shrank, the salt would become more and more concentrated, leading eventually to tiny particles of salt that would be carried inland by the breeze for long distances. I would propose instead to combine your idea with solar stills to generate fresh water for your pumps, returning brine to the ocean.

 

I am not sure how desalination plants work but how do they compare with solar stills ? 

[exchemist]

1 hour ago, paulsutton said:

I am not sure how desalination plants work but how do they compare with solar stills ? 

The difference is the way they get their energy input to work against entropy, basically.

Desalination plants often use reverse osmosis, in which pressure is used to force water molecules through a semipermeable membrane that does not allow the larger, solvated, salt ions through. (Although an individual Na+ or Cl- ion is smaller than an H-O-H molecule, these ions in solution are surrounded by a solvent "cage" which is quite tightly bound to it and makes their effective size a lot bigger.) Alternatively distillation is used, often under reduced pressure to permit boiling at a relatively low temperature. (Boiling greatly increases the surface area for evaporation, accelerating the process, due to the surface area of the bubbles).  The very large desalination plant at Jebel Ali, in the UAE, used that method, I remember, from when I lived in Dubai in the 1980s. It employed waste heat from the Jebel Ali steam power station - quite clever. 

A solar still relies on heat from the sun, rather than an artificial energy input. So the energy input is in a sense "free"  - and non-polluting, of course - but you are limited to the energy density of sunlight. Solar stills also have to rely on evaporation at atmospheric pressure, which further constrains their capacity.  

Edited May 2, 2023 by exchemist

[geordief]

Nemo's Garden in Italy is interesting.Is it an underwater still? 

https://edition.cnn.com/travel/article/nemos-garden-underwater-farm-italy-spc-intl/index.html

 

"Floating six to 10 meters underwater,

plants in Nemo’s Garden are separated from any outside pathogens and pests,

while still having access to freshwater that occurs as a result of desalinated condensation within the biospheres, Gamberini says.

Also, he notes, the relatively steady temperature of the sea water is an ideal environment for plant life"

[exchemist]

19 minutes ago, geordief said:

Nemo's Garden in Italy is interesting.Is it an underwater still? 

https://edition.cnn.com/travel/article/nemos-garden-underwater-farm-italy-spc-intl/index.html

 

"Floating six to 10 meters underwater,

plants in Nemo’s Garden are separated from any outside pathogens and pests,

while still having access to freshwater that occurs as a result of desalinated condensation within the biospheres, Gamberini says.

Also, he notes, the relatively steady temperature of the sea water is an ideal environment for plant life"

This article explains almost nothing, so it's impossible to say. It looks like a gimmick to me. What's the point, especially since the light has to be supplemented with electricity? 

[geordief]

23 minutes ago, exchemist said:

This article explains almost nothing, so it's impossible to say. It looks like a gimmick to me. What's the point, especially since the light has to be supplemented with electricity? 

Not sure.It is an experiment ,apparently.

 

This is a better article

 

https://oceanographicmagazine.com/features/italys-underwater-farmers/

 

 

[mistermack]

On 12/30/2022 at 11:53 PM, Lady of Elms said:

I've got some background in environmental sciences, and the very first thing you need to "green" anything is water retention and stable substrate.

What I find is that most deserts are not featureless sand dunes, they have plants growing, but plants that are adapted to low rainfall. If you were trying out this method of increasing rainfall, you would naturally start in a suitable location, where more rain would naturally increase the density of the existing greenery. 

Most of Australia is technically desert, but not a lot of it is empty dunes. And in many other parts of the world, the deserts are kept less green than they would naturally be, by intensive grazing with goats. 

[paulsutton]

9 hours ago, exchemist said:

The difference is the way they get their energy input to work against entropy, basically.

Desalination plants often use reverse osmosis, in which pressure is used to force water molecules through a semipermeable membrane that does not allow the larger, solvated, salt ions through. (Although an individual Na+ or Cl- ion is smaller than an H-O-H molecule, these ions in solution are surrounded by a solvent "cage" which is quite tightly bound to it and makes their effective size a lot bigger.) Alternatively distillation is used, often under reduced pressure to permit boiling at a relatively low temperature. (Boiling greatly increases the surface area for evaporation, accelerating the process, due to the surface area of the bubbles).  The very large desalination plant at Jebel Ali, in the UAE, used that method, I remember, from when I lived in Dubai in the 1980s. It employed waste heat from the Jebel Ali steam power station - quite clever. 

A solar still relies on heat from the sun, rather than an artificial energy input. So the energy input is in a sense "free"  - and non-polluting, of course - but you are limited to the energy density of sunlight. Solar stills also have to rely on evaporation at atmospheric pressure, which further constrains their capacity.  

Cool,  thank you for this.

[mistermack]

I just saw a piece on the BBC news channel about a rather similar spraying exercise as an experiment on cooling at the Great Barrier Reef. 

They are hoping to create more cloud cover in the area, reflecting more sunlight, and cooling the reef. It's not the same purpose at all as what I suggested in the OP, but it's remarkably similar in what is proposed. 

I was proposing it as a way to get more rain falling over deserts like the Australian Outback, rather than cooling anything. But the spraying idea is much the same. I wouldn't want the salt water to completely evaporate, the way they are suggesting. Too much salt in the atmosphere, and no control over where it would fall. I would aim at a small proportion of the spray falling back into the water, taking all of the salt with it. 

But it's interesting to see that spraying on a huge scale has been costed, and is being tested. Maybe they read this thread and pinched the idea ! 

https://www.abc.net.au/news/2023-06-28/tiny-cloud-brightening-particle-research-climate-change-icnaa/102524408 

 

 

[TheVat]

So what is your own opinion on the topic?

Would take terawatts, looks like, and deserts that border oceans tend to be that way because they lack onshore winds and tend to rapidly evaporate any water that does come their way.  IOW, world's most expensive fountains.

A mosaic of indigenous land use practices, however.....

https://www.smithsonianmag.com/science-nature/great-green-wall-stop-desertification-not-so-much-180960171/

[Genady]

Did anybody mention indigenous peoples living in deserts?

[mistermack]

5 hours ago, TheVat said:

Would take terawatts,

Where's the evidence for that?  

 

5 hours ago, TheVat said:

deserts that border oceans tend to be that way because they lack onshore winds

Not necessarily. You can have dry winds coming in off the ocean, from a Hadley Cell. And I did specify the obvious point earlier, that this kind of installation would only be sited where there are onshore winds, and would only be turned on when the wind was in the right direction. To me, that's stating the obvious. You're not going to just rush in without doing the research. 

As far as evaporation goes, what's the problem? It can fall as rain again. The Amazon creates it's own weather, from evaporation. The only way you can lose the water, is if it blows back out to sea. You can research prevailing winds to forecast what happens to the moisture you have produced. 

If you were successful in altering the climate, it's possible you could get rivers flowing and derive hydro-electric power from them. 

[TheVat]

1 hour ago, mistermack said:

Where's the evidence for that?  

 

It may help to research the enthalpy of vaporization of water.   The sun pours terawatts on that water and the adjacent deserts remain desert.

I looked up the thread and see you were not interested in pursuing that when Seth suggested it, so I'll leave it be.

Another error I spotted was the assumption that water vapor is cooling.  Water droplets are cooling (we call clusters of them "clouds"), but vapor is a GHG and magnifies the GH effect.  Without megatons of condensation nuclei, you could end up making that desert a hot sticky hellhole.  

You also have the sinking branches of the Hadley Cells suppressing rain at the subtropic latitudes where many of these deserts are located.  

Would not money be better spent encouraging farmers to decrease their goat flocks and try the various measures in my linked Smithsonian article on the Sahel?  Building vegetation and enriching soils may be the better longterm solution.

[mistermack]

7 minutes ago, TheVat said:

It may help to research the enthalpy of vaporization of water. 

That was a misconception I didn't expect from you. You break the water up into a spray, as in the Australian example I posted, where they are experimenting on creating clouds to cool the barrier reef. The energy to evaporate the water comes from the air, not the sprayer. The onshore wind will be cooled and humidified, and the energy input from man is restricted to creating spray droplets, not evaporating the water. 

[StringJunky]

8 hours ago, TheVat said:

A mosaic of indigenous land use practices, however.....

https://www.smithsonianmag.com/science-nature/great-green-wall-stop-desertification-not-so-much-180960171/

That's a head turner. Makes a lot of sense. I should have realized actually that indigenous people understand the rythms of their locality. The Amazonians made charcoal infused soil called Terra Preta;

Quote

The technique of using charcoal to improve the fertility of soils originated in the Amazon basin at least 2500 years ago. The native Indians of the region would create charcoal, mix it with organic matter and broken pottery, and incorporate it in small plots of land from 1 - 80 hectares in size. Terra Preta, as it is known in this area of Brazil, remains highly fertile until today, even with little or no application of fertilizers. And this is in a region of the world known for its highly infertile tropical soils.1

Local inhabitants have always known Terra Preta to be uniquely fertile, but it was largely unknown worldwide until a scientist named Wim Sombroek began to research it intensively. It was from Wim's passion for Terra Preta soils that interest in creating Terra Preta Nuova arose, which eventually was called biochar. In addition to their high char content as mentioned above, Terra Preta soils are characterized by high phosphorus content reaching 200-400 mg P/kg, and higher cation exchange capacity, pH and base saturation than surrounding soils.

Terra preta Wim Sombroek
Wim Sombroek explaining Terra Preta characteristics in Manaus, Brazil.
Organic carbon, meaning carbon-based molecules that have their origin in anything that was once living, makes topsoil black or brown in color. It is commonly known that fertile soils are black, and perhaps less commonly known that this fertility arises from the presence of organic carbon. In tropical and subtropical regions of the world, organic carbon does not tend to accumulate in soils, and so they are generally white, yellow or red in color. The reason is that because of the heat and / or humidity, organic matter decomposes rapidly and directly to CO2, and hence little to no organic carbon is present in the soil, only the sand, silt, clay, stones and minerals.

In more temperate regions of the world, organic matter decomposes slowly enough that it remains on and within the top layer of soil as it breaks down into smaller and smaller molecules. Some of this organic carbon decomposes fully to CO2, while some of these so called humic molecules bind to minerals and become relatively stable, enduring for hundreds to thousands of years.

https://biochar.info/?p=en.terra_preta#:~:text=The technique of using charcoal,1 - 80 hectares in size.

I wonder if that technique could be advantageous to the desert dwellers that are trying to make their land more productive. The Amazon areas that have it, it constitutes 4-9% of the surface soil.

Edited July 7, 2023 by StringJunky

[TheVat]

11 minutes ago, mistermack said:

That was a misconception I didn't expect from you. You break the water up into a spray, as in the Australian example I posted, where they are experimenting on creating clouds to cool the barrier reef. The energy to evaporate the water comes from the air, not the sprayer. The onshore wind will be cooled and humidified, and the energy input from man is restricted to creating spray droplets, not evaporating the water. 

Makes no sense.  If wind and sun aren't doing it, the nozzles of man aren't going to do diddleysquat.  Expensive fountains.  Like the Bellagio casino in Vegas.  It's mainly sun that evaporates, and the shore waters are already having their surface increased by the wind roughing them up.  

Even if you did miraculously lob a few tiny clouds landward, the desert air would just boil them away and you would, as I mentioned in previous post, just have a slightly more humid patch of sky retaining slightly more insolation heat.  

 

[StringJunky]

Another fact about the Amazon is the humus layer is only 2-5cm deep! That's sand and clay underneath and very few minerals... everything is within the  growing zone. Heat and moisture rapidly degrades dead matter to keep the system going.

Quote

The rainforest feeds itself. Most nutrients are absorbed by the plants and do not get into the soil at all. It's a kind of supernatural cycle. The few plant remains that do reach the ground — leaves or branches — are decomposed in no time by fungi and bacteria thanks to the year-round warm and humid climate. The nutrients released, such as potassium, calcium and magnesium, are immediately reabsorbed by the roots.

There is virtually nothing left for the soil. Nor can a fertile layer of humus ever form. Just a few centimetres below the top layer of soil, there is nothing more than sand or clay. All nutrients in the rainforest are stored in the plants themselves, not in the soil. For agriculture, rainforest soils can therefore only be used for very short periods of time. 

https://www.dw.com/en/the-amazon-nutrient-rich-rainforests-on-useless-soils/a-50139632

[mistermack]

2 hours ago, TheVat said:

Makes no sense.  If wind and sun aren't doing it, the nozzles of man aren't going to do diddleysquat.

You should let those people running the experiment on the Barrier Reef know, then. 

" Daniel Harrison, from the Southern Cross University's Reefs and Oceans Research Cluster, heads the team, which has been shooting sea water from canons for three years to brighten clouds in a bid to help tackle global warming." 

They are totally evaporating the sea water, so as to shoot salt crystals into the air in a bid to brighten clouds, making them more reflective. 

Someone should tell them that their nozzles are doing diddleysquat. They would surely be grateful to you. 

 

Edited July 8, 2023 by mistermack

[geordief]

1 hour ago, StringJunky said:

 

Another fact about the Amazon is the humus layer is only 2-5cm deep !

A very interesting  fact I was unaware of.Is that why the Tropical rain forests are said to be fragile ?

 

They have no "reserves" in the ground  once they have been lost?

[mistermack]

6 minutes ago, geordief said:

A very interesting  fact I was unaware of.Is that why the Tropical rain forests are said to be fragile ?  They have no "reserves" in the ground  once they have been lost?

In general, that's right. They are generally on pretty poor soil, because of the high rainfall, nutrients tend to get washed out. When they burn down amazon forestry, they usuall only get a few seasons of productivity on the cleared land, before it becomes fairly exhausted. In the forest, there's an intensive 'industry' recycling nutrients rapidly as stuff falls out of the trees. From what I remember, the tree roots tend to grow outwards, rather than down, because the deeper soil is barren.

[StringJunky]

31 minutes ago, geordief said:

A very interesting  fact I was unaware of.Is that why the Tropical rain forests are said to be fragile ?

 

They have no "reserves" in the ground  once they have been lost?

Yes, that's it. It is literally a self-contained system in an otherwise hostile environment. The solution for fixing a desert is right there, but I've no idea what the critical mass looks like, when it requires no more intervention.

19 minutes ago, mistermack said:

In general, that's right. They are generally on pretty poor soil, because of the high rainfall, nutrients tend to get washed out. When they burn down amazon forestry, they usuall only get a few seasons of productivity on the cleared land, before it becomes fairly exhausted. In the forest, there's an intensive 'industry' recycling nutrients rapidly as stuff falls out of the trees. From what I remember, the tree roots tend to grow outwards, rather than down, because the deeper soil is barren.

That default horizontal interlocking of roots is what creates a fantastic framework for things to latch onto, decompose into and compress in a compact manner to create a sponge to hold water and nutrients. The ultimate 'design' aim I think is to make it waterproof at the subsoil/humus layer interface.

Edited July 8, 2023 by StringJunky

[TheVat]

14 hours ago, mistermack said:

You should let those people running the experiment on the Barrier Reef know, then. 

" Daniel Harrison, from the Southern Cross University's Reefs and Oceans Research Cluster, heads the team, which has been shooting sea water from canons for three years to brighten clouds in a bid to help tackle global warming." 

They are totally evaporating the sea water, so as to shoot salt crystals into the air in a bid to brighten clouds, making them more reflective. 

Someone should tell them that their nozzles are doing diddleysquat. They would surely be grateful to you. 

 

The GBR experiment is different in several ways from what we are discussing, so it does not address the issues I was talking about.  BTW, any positive results reported on that experiment?  

14 hours ago, geordief said:

A very interesting  fact I was unaware of.Is that why the Tropical rain forests are said to be fragile ?

 

They have no "reserves" in the ground  once they have been lost?

One of the reasons environmental groups have pushed boycotts on S American products like tinned beef.  Forest clearing gets beef producers a couple years of grazing, then the land is a ruined mess and has to be abandoned.

[StringJunky]

1 hour ago, TheVat said:

The GBR experiment is different in several ways from what we are discussing, so it does not address the issues I was talking about.  BTW, any positive results reported on that experiment?  

One of the reasons environmental groups have pushed boycotts on S American products like tinned beef.  Forest clearing gets beef producers a couple years of grazing, then the land is a ruined mess and has to be abandoned.

If they charcoaled the trees they cut down and infused that with desirable minerals before working it in the gound, they might have a more sustainable system. They need to stop it leaching, and that's what the terra preta does. It holds onto the nutrient anions and cations until the plants need it.

Edited July 8, 2023 by StringJunky

[TheVat]

7 minutes ago, StringJunky said:

If they charcoaled the trees they cut down and infused that with desirable minerals before working it in the gound, they might have a more sustainable system. They need to stop it leaching, and that's what the terra preta does. It holds onto the nutrient anions and cations until the plants need it.

Be great if that worked.  And realistically I don't see many SA ranchers opting to let cattle graze in the rainforest (though forest grazing is a real thing now), so soil modifications of cleared pasture is a more likely approach.  Which hopefully would reduce the forest clearing by creating longterm pastures.