Can we turn deserts green?

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If there was a big red button that would just demolish the internet, I would smash that button with my forehead. From the BBC, this is The Interface, the show that explores how tech is rewiring your week and your world. This isn't about quarterly earnings or about tech reviews. It's about what technology is actually doing to your work, your politics, your everyday life, and all the bizarre ways people are using the internet. Listen on bbc.com or wherever you get your podcasts.

I'll start with the pouring I guess. Yeah, that is some salty water. Give it a little mint. And now we pour this salty water into the keg. Okay, so that's salty water. Now I turn this kettle on. Now we just wait for it to boil. This is CrowdScience, the show where we boil questions in the kettle of curiosity. I'm Alex Laughbridge. So you're probably wondering why I'm boiling a kettle of salt water and making this BBC studio smell like a dock? Well, it's because of a question from listener Yusuf.

yeah my question is can we re-agree in the deserts So basically trying to put water back in the deserts. Rwy'n mynd i'n mynd i'n mynd i'r cymdeithasol, sut mae'r cymdeithasol, sut mae'r cymdeithasol yn mynd i'r cymdeithasol. Maybe it could be a solution to actually divert the water into the deserts. Wow, I hadn't even thought about that. By doing it, you're lowering sea levels. There are so many parts to this.

Okay, if we manage to, you know, bring water into the desert, perhaps sort of re green parts of it, would you want to move there? Would you set up, you know, a little plot? Oh uh uh absolutely, absolutely. Where okay, where? Where which which desert would you go to? I've n I've never actually been to the desert, you know. I mean, although I uh came from Algeria originally, I'm from Algiers, which is the north of the country.

And I've never been down there, but all the people who have been there, they just how beautiful it was down there. You know, all the dunes. uh the mountains and you know the the solitude So Yusuf wants to know if we can bring water to the deserts of the world, despite not actually having been to one. But what actually is a desert? You might be thinking of the huge sand dunes and desolate landscapes of the Sahara or Gobi, places that receive less than 250mm of water per year.

But deserts exist on a wide spectrum with varying levels of plant, animal, and human life. This makes it sort of difficult to define, but generally speaking, a desert is an extremely arid environment where the limited amount of water makes it difficult for most life to thrive. And deserts are growing. Desertification is a process where fertile land declines over time. According to the United Nations, roughly one million square kilometers of healthy land is degraded every year.

Desert is a natural phenomenon on the earth. If the desert is stable, it is fine. We can live by it is. Deservication means that a natural land like a grassland or a shrub land somehow becomes drier and drier and then converted to desert.

This is Yan Li, a professor of geographical sciences at Beijing Normal University in China. He started thinking about what might bring more water to the desert by focusing on what mechanisms take that water away in the first place. The very conditions that lead to desertification. Concepts that were first understood in the nineteen seventies by a scientist named Jules Charney.

Charney found that human activities play a significant role in desertification. When you have too many livestock, those animals eat all the grass, so the grass is degraded to bare ground or to sand. And when this happens, the albedo of the desert surface changes. So albedo means the reflectivity of the surface. If the albedo increases, that means more solar radiation is reflected back to the space. Something with high albedo is lighter in colour, or even white, and reflects sunlight. Think snow.

A low albedo surface would be darker and could soak up more heat, think like pavement on a hot summer day. Then Charlie found that with the increasing albedo they will inhibit When the albedo is higher. less heat is absorbed by the ground. This reduces evaporation into the atmosphere, which reduces cloud formation and therefore leads to less rainfall. What if we do it oppositely? What if we can

decreased surface albedo. Will that increase precipitation? So Then the solar panel is a perfect candidate. So Jan and his team ran a simulation, a model where twenty percent of the land across the entire Sahara Desert was covered in solar panels. Because the solar panels, they have a dark surface. it means they have a lower albedo or lower reflectivity. But they didn't stop there. They also ran a version of the simulation where they covered the Sahara with both solar panels and wind turbines.

But why add the wind? If we have wind turbine installed on the surface, it will change surface roughness. You can understand roughness as a surface friction. So with more friction, the more energy could be transferred into the atmosphere through turbulence. And the turbulence creates weather and creates those clouds. So by making the surface of the earth more rough, it will help send that hot air with more moisture up into the sky, creating clouds and eventually rain.

If we change the albedo of the Sahara, as well as the surface friction, thereby creating more clouds, How much more rainfall could this bring in? The average precipitation of the entire Sahara Desert will be doubled. if we have such massive solar and wind farms there. Through these simulations, Jan and his team modelled what would happen in the Sahara, but might it work elsewhere?

Would this same phenomenon happen in the Gobi, in Mongolia and China, or in deserts in Saudi Arabia? It seems only the Sahara Desert we can have this uh significant precipitate increase. So we think that there are some reasons to explain this. First, the Sahara Desert has the highest surface albedo of all this desert. So that means if we put a dark solar panels on Sahara, it will

lead to the largest surface albedo decrease compared to other deserts. Another reason is because the Sahara Desert it is close to the ocean. So the ocean moisture can easily go into the Sahara Desert. But for the Gobi Desert And look at desert in the Middle East, they are far away from the ocean. So even you create more warm air or increase the convection activities there, you will not have a huge impact on the clouds and the precipitation. Essentially you can't make water out of nothing.

But even if you're on the coast, you've got to find a way of bringing that water in. And here is where Jan and his team came up with another way to change the albedo of the desert. Vegetation actually played a very important role or essential role for the results we found. When the Sahara Desert if they have more rainfall, the vegetation will recover, and with this recovered vegetation,

The vegetation can further decrease surface albedo because vegetation they cover the bare ground and the bare desert decrease albedo. With the additional vegetation, it will also make the surface. as rougher or more friction. It's become a positive feedback loop. For water to come to the desert you really need vegetation to keep the ground as rough and unreflective as possible.

But to keep vegetation alive, you need water, so it might seem like this chicken and egg situation, but it points to a key concept to changing water that's available in the desert. The water cycle. You may have heard the water cycle. Because the the water is cycling or recycling in the earth system.

That means if we have surface water coming out from the vegetation or from the soil, those water vapor will go into the atmosphere and it travels So the wind and uh at ideal condition those moisture will fall into the ground again as precipitation. So every part of the world is connected through this moisture recycling process. So larger scale renewable solar and wind farms could actually change the weather itself.

altering the albedo and increasing the winds, leading to more rain and vegetation, which leads to more rain and vegetation in a positive feedback loop.

But here's the thing, right now it's just a simulation. And the amount of solar panels and wind turbines would be enormous, covering about 20% of the Sahara. But for deserts where there are already clouds, is there a way? In what's often called the driest place on earth, the Atacama Desert, there's a technology that's been pulling water out of the air.

The technology of harvesting it was created in Chile around fifty years ago. The technology is very simple. The idea of this technology is to harvest water from the clouds. In the desert. This is Virginia Carta, a geographer and assistant professor at the Universidad Mayor in Chile. She's also an expert in building fog collection systems. Fog harvesting is exactly as it sounds. In deserts across the world where clouds are present, it's a way of pulling water out of the sky and onto the ground.

But how do you catch a cloud? First you need the cloud, then you need a mountain, which is facing this cloud, then you need wind, and then you will find these collectors, so two posts and the the mesh being supported. And then many or million little drops are gathered together and then are going down uh by gravity So then you can use a pipeline and then you can harvest the water. Usually we use uh water tanks in the middle of the mountain.

So that is the way. Literally the mesh is harvesting the water from the cloud. Here's the thing, to catch a cloud, you've got to make sure that you're not too high and not too low. That sweet spot is known as the zone of interception. This is the altitude at which fog harvesters can collect the most water. So once you've placed your collector in a decent spot, how much water can it actually harvest?

In the very north of Chile, the average is two liters by one square meter, then you can have other places with seven, seven liters by one square meter per day. So if you want to collect, for instance, two hundred liters per day. Our listener is really interested in how we can fog harvesting help with that, you know, help with this sort of agricultural irrigation that could, you know, make it easier to grow plants in these areas.

Yes, uh in fact we are conducting a project in another place of the Atacama Desert, we are cultivating hydroponics using fog water. So if you are thinking in future strategies for Atacama or other places, right places, of course it's possible. Also we are thinking in to promote the the use of water for the regeneration of e ecosystems. So yes, you can use it for population, for irrigation, for cultivation, etc. How does the water taste?

Sweet for me, you know? It's it's delicious. I started with this when I was twenty two. I was studying geography. And I remember how happy I was when I drink my first glass of of water. Now uh it's amazing to see the communities Catching this water because they don't have any other water.

While fog harvesting is incredibly promising, there are a couple of drawbacks. The amount of water you can harvest is a lot smaller compared to other techniques, and you need to be in a place that has fog, which is usually near the coast. But there's one technique that could bring a lot more water to dry regions that are far from the coast. We'll be finding out about that next.

If there was a big red button that would just demolish the internet, I would smash that button with my forehead. From the BBC, this is The Interface, the show that explores how tech is rewiring your week and your world. This isn't about quarterly earnings or about tech reviews. It's about what technology is actually doing to your work, your politics, your everyday life, and all the bizarre ways people are using the internet. Listen on bbc.com or wherever you get your podcasts.

You're listening to Crowd Science from the BBC World Service. I'm Alex Lathbridge and this week we're answering question from listener Yusuf. Who wants to know if we can make the deserts green? So far, we've found out how solar panels and wind turbines could help change the weather in the desert into something more hospitable for agriculture. And even though we can harvest fog, it's probably not enough.

enough to achieve Listener Yusuf's vision of re-greening the desert. So what if we could use seawater? Well greening the deserts is a, I have to say, is an ambitious uh objective, but certainly we can green parts of the desert. if we can provide the water that's sadly missing. And that's where desalination comes in. This is Chris Sandsom, a professor at the University of Derby in the UK. His research looks at how we can use the sun to desalinate water.

Desalination is a process that's commonly used around the globe to remove salt and other minerals from seawater to create freshwater. This is important because salty water isn't very good for making soil that you can grow things in. The way that most of the large desalination plants in the world work at the moment They work by forcing seawater through membranes that trap the salt and the water goes through the membranes.

Sounds simple, but it's it's quite complicated. It involves huge amounts of pressure, huge pumps to pump the seawater through the membranes, and that's called reverse osmosis R O. And that's the way that most of those desalination plants in the Middle East, that's how they work. There are something like thirty of those plants in Saudi Arabia today, but each one uses a huge amount of energy. They use something like ten thousand barrels of crude oil each day for each plant. Or

You can go down the route of thermal desalination. Basically, it's like putting salty water in a kettle and boiling it up. Okay, so water has boiled. You then collect that steam in a cold chamber where it condenses out. We caught some of the the steam that came out in a little bowl, leaving you something that's close enough to pure water. It should be fresh water with no salt. I'm gonna give it a little try.

That is actually very clean. That there is no salt in that. And I think I actually might leave the kettle here because the next person to use it, like they make a cup of tea, that's gonna be a really surprising cup of tea. The desalination units that Chris is developing rely on energy from the sun to boil water rather than using fossil fuels. We're looking to develop

a small desalination system that could be used in refugee camps, disaster zones, where basically you need drinking water very quickly. So in that case you can make it using plastic lenses that focus sunlight onto a pipe through which runs a fluid, which can then heat up and then can evaporate brackish water or seawater to give you H two O basically. Scaling up Then you start to look at very, very large concentrating mirrors in the desert to concentrate a lot of sunlight onto very large pipes.

Which can then evaporate a lot of seawater and uh condense a lot of steam to give you very large uh volumes. So how much water are we talking here? From the sun in a hot country we get about one kilowatt. per square meter a kilowatt hour would give you about two liters of water an hour. For the larger units, you can just keep scaling up. The more mirrors you have

But you can just keep adding those areas of mirrors, more pipes, more seawater going in. You can scale that up to any any size you like. So really the the sky is the limit as far as that's concerned. And so would this be enough? Would it provide enough water to help re-green desert areas?

Certainly, assuming that you have the source of seawater, so you're either by the sea or you're piping the seawater to where you need it, yes. The world already desalinates approximately thirty four point eight billion cubic metres of water per year. And those needs are going up. I think to simply to keep pace with population rise and climate change, that probably has to double or treble by twenty fifty.

And for your questions about greening the desert, then well many times that, maybe ten times that. And so these desalination plants are taking salt from the out of seawater. What happens to the salt? If you fly over desalination works, you will find very often large areas of salt that you w you will see quite clearly'cause it's white on the ground in the deserts.

just dumped basically. Yeah, it is a byproduct of the process and at the volumes in which that salt is produced, there is nothing else you can do apart from just leave it there on the surface or bury it. While desalination is incredibly powerful, the way that it's done today with reverse osmosis is very energy intensive, often relying on fossil fuels.

And the solar-powered units are still in development. And no matter how you do it, you're still left with huge amounts of leftover salt, which can damage the environment around these plants. But all these methods to produce fresh water, they all have their trade-offs, right? So desalination, one of them is is this production of really salty water that you've got to somehow get rid of. This is Alan Condron.

He studies climate change and more specifically how melting ice affects ocean circulation. I'm a research professor at the Woodshill Oceanographic Institution, which is in the United States of America. So you desalinate them and you're each left with a bunch of salt. Right, you know you are. Who's got space for salt? It's a hu no it's a huge problem in um in the Middle East is that you end up injecting sort of really brackish, very salty water back into the ocean.

And that's sort of actually that's actually a pollution in itself for the marine ecosystems you can't tolerate really high salt levels coming back out of these D cell plants. Now, Yusuf wanted to know if bringing seawater to the desert could help reduce the impact of rising sea levels. So who better to ask than an ocean climate expert? So the rate of sea level rise is is going up, we know it's accelerating.

But on average, since about twenty eighteen from to now, about uh three point seven uh millimeters a year. It's something like one sort of trillion cubic metres of water a year. Alright, little bit of quick maths. Thirty-four point eight billion cubic meters of water is desalinated each year. That's only about three percent of annual sea level rise.

At the risk of people hundreds of years in the future calling me a fool, it's looking like it would be nearly impossible to scale up desalination to keep pace with increasing sea levels.

So, sorry Yusuf, it's looking like at least that part of the equation doesn't quite work out. But Alan is no stranger to trying out unconventional ideas. I developed a model that simulates icebergs and how they melt and how they drift in the ocean, being pushed by the ocean currents and by the winds. So then we took this model and I said, Okay, well that's let's see if we can use it to tow icebergs to locations that are you know have water shortages.

Allen then tested two scenarios, one towing Antarctic icebergs to Cape Town in South Africa, and then to the UAE. So I mean we're talking about icebergs that are getting close to a kilometre in size. And if you want to move something like that, you're going to need like ten really high performance tugboats to move that. So our closest tow was from Antarctica to Cape Town, that's two thousand five hundred kilometres.

the sort of speeds that we were sort of looking at or guessing that these icebergs could be moved at, which is around about close to a knot, you know, you're looking at a tow time of somewhere between like fifty to a hundred days. And then if you go even further and you say you wanted to move it to Saudi Arabia or the UAE. kind of mind bogglingly, you know, long uh transit times of say two hundred to four hundred days of pulling this iceberg.

And I I'm no expert on the sea and the temperatures, but I'm pretty sure Antarctica very, very cold and as you get closer to perhaps continents, the water may be a little bit warmer and the ice that you're towing might melt. Yeah, that is a problem. Especially um so for our UAETO, you're looking at pulling an iceberg through the Indian Ocean for quite a few months. You know, you're looking at sort of twenty five degrees C plus water temperatures.

That's going to take a huge toll on the iceberg as it as it melts. The route to Cape Town, our shorter route, as you start to move northwards from Antarctica to the same. the water actually stays cold for quite a long time. It's not until sort of the last month or so of the iceberg tow to Cape Town that you start to move away from the sort of protection of the Antarctic waters and you start to pick up more sort of subtropical

Cape Town waters. So what happens with the iceberg once it gets to somewhere, once it gets to port? What do you do with it then? That is the sort of million dollar question, right? As you get quite close to your destination, you know, the ocean gets shallower.

So if you've got this really, really big iceberg, in some locations, quite a few actually, the bottom of the iceberg will then hit the hit the seafloor. It might sort of be stuck, you know, fifty, hundred miles offshore or something. And so how do you do that? I'm gripped. So that's when I think you're starting to touch into the realms of science fiction a little bit. One of the ways put forward is if your iceberg's very, very big, you can essentially put machinery on it and

drill into it. Similar to like open cast mining, where you would kind of go down into the iceberg a in a sort of circular way, sort of digging, sort of burrowing in to the middle of the iceberg. And it's sort of extracting the ice as you do that. Drop the iceberg off in a dry dot.

drain the seawater out, let the fresh water melt, and then collect it. Ta da usable water. You know, that uh example, you your iceberg needs to be a lot smaller though, right? Because you're thinking about something that's maybe you know the same size as like uh A cruise ship sort of size vessel or something like that. So the model didn't look at a couple of key considerations. mainly the cost and the fuel involved in towing an iceberg across the world.

Not to mention you've got melting icebergs that could collide with ships, uh they could get grounded when they get close to shore, and what do you actually do with the iceberg once you get it there? But I still wanted to know if Alan thought that this might be possible one day. It always seems like there's somebody just about to actually go and do a an actual tow. Um it never seems to quite materialise.

You know, yes, you know, I have a a model that simulates icebergs and how they they melt in the ocean. But you know, it like it's just a model, right? Every model needs testing and it needs proving and and validating.

So we've heard some really interesting ways of getting water to the desert desalination, fog harvesting, or even changing the weather itself. But if we want to re green the desert, we need to understand what kind of green it should be. In other words, we need a plant scientist to understand what kinds of plants could survive in such an environment. My name is Simea Aide González Carranza.

I had been working in the University of Nottingham for the last twenty five years. I would say instead of trying to green the desert or to bring water to the desert, I think we need to protect the life that is there. Zinier has studied many desert plants. including the Mesquite tree native to Mexico and the southwest of the USA. Mesquite is a tree that is native from the Americas and is very well adapted to the semi arid zones of the Sonoran desert and

and all the deserts in Latin America generally. Mezquite is a tree that can actually help other plants to grow. Because when it sheds its leaves, those leaves decay and make richer soil than the typically sandy of rocky desert has, and that provides a more nutritious home for future plants. They also fix nitrogen in the soil, which is a key element for plant growth.

Sounds good, right? I think one of the problems that we have is that we tend to think okay, we will generate these crops that are resistant to drought and to to heat. we don't know what it's the extra problems that will generate. And that's the case for example with the introduction of the mesquite in in Africa.

Throughout the course of her work with communities in Mexico, Kenya and Tanzania, Xinia has seen the unintended consequences of introducing new species to the desert, even species like Mesquite, that are already well suited to dry environments. One such example can be seen in South and East Africa, where mesquite was introduced to help stop creeping desertification. So they thought well this is a a good idea, let's bring those trees, we stop the desertification, we stop the erosion.

They survived very well because the root grow quite deep. And if there is no water around, they can get water from the subterranean waters. And maybe they can survive with as little as 100 millimeters rain in a year or even less. So they are very well adapted to the conditions really. And the mosquito trees did well. In fact, they thrived. So was it the first step to regoing the desert? Not quite. These trees started to compete with the native plants and the native ecosystems.

Communities didn't like the tree because the trees start to produce these pots and the the goats like the pot. The goats ate the sweet pods, and that wasn't good, because unlike humans, goats don't have their own dentists to deal with cavities. Local communities actually ended up suing the government because of the impact of the imported trees. While bringing greenery to the desert might seem like a positive, the impact on local ecosystems can be life changing.

Zinia says that these types of unintended consequences can take place with any imported plants, even the ones that have been genetically engineered to survive and thrive in desert conditions.

I mean I I start working as a plant scientist with genetic engineering. And through my work and through working with the communities I am really convinced that We have to do less than By introducing plants maybe we will generate good crops for a while, but that is to the expense of a lot of water and what we have seen is that if you use a lot of water in those crops The communities that live around in the desert are the ones that suffer

So in the long term it can remove more water from the ecosystem and actually cause an increase speed up desertification. That's correct. Yes. Rather than trying to grow big fields of crops for exports, Xinia suggested that the group of the groups are the to smaller scale and more sustainable ways to grow just what's needed.

What we are trying to do with these communities is helping them to have backgardens where they can grow plants. But also we need to be a little bit more humble in understanding that Communities from the desert have been living there for centuries and they understand the desert. They have a lot of knowledge.

And I'm speaking about traditional knowledge. Hm. Yeah, it's just like if you make the desert green, you know, we go to Mexico, we go to Kenya, we say, Look, here's a nice green desert and then go away. It's like, well, all you've done is change everything. The people who were tending this land for hundreds, thousands of years now have to try something new. I mean, honestly, I thought, you know, the more

green we had, the better it would be in the long term, fifty, a hundred years. But actually that isn't the case. I don't think so. I mean I think that the the best that we can do is really understand the desert, respect it and try to uh to work with it. Yusuf, it might be possible to get more water into the desert. It could be by converting seawater into fresh water, harvesting clouds, or even changing the weather in the desert.

But if we want to combat desertification, we're going to need to understand why it's happening and take on the root causes, things like fossil fueled climate change and intensive agriculture. But we need to realise that deserts aren't inherently bad. They're an ecosystem like any other, and attempting to change them into green forests just because we can are

Could be terrible in the long term for the environment and the people who call it their home. Now, before we head off to start boiling kettles and building fog harvesters, here's Yusuf with the credits. That's it for this edition of Crowd Science. Today's question was from me, Youssef, in the UK. If you have a question for the CrowdScience team, email crowdscience at bbc.co.uk. This episode was produced by Sam Baker and presented by Alex Lethbridge. Thanks for listening. Goodbye.

If there was a big red button that would just demolish the internet, I would smash that button with my forehead. From the BBC, this is The Interface, the show that explores how tech is rewiring your week and your world. This isn't about quarterly earnings or about tech reviews. It's about what technology is actually doing to your work, your politics, your everyday life, and all the bizarre ways people are using the internet. Listen on bbc.com or wherever you get your podcasts.