This Episode is brought to you by Brilliant Every year the deserts of Earth expand a little
more, swallowing up huge tracts of previously fertile land. We’re working hard to slow or stop that,
but how do we go about reversing it? So today we will be looking at reclaiming
the deserts. In many ways, when it comes to making desert
fertile, it’s more about repair and reverting to a prior state than introducing something
new. A concern in this series is the impact of
some of these techniques on existing ecosystems, but our current deserts aren’t entirely
natural. We have a lot of options, from the low tech
to high tech, subtle to brute force. Some are slow, some fast, some can be implemented
locally and others require vast regional or even global efforts. Which ones we might use will vary on circumstances. Some tactics rely on altering the weather,
others on diverting freshwater from existing supplies or creating new freshwater by desalination. Some focus on conserving water or getting
the most out what supplies you have, while others might involve gene-tailoring species
to survive on saltwater, skipping desalination entirely. But just like terraforming a planet, there’s
more to reclaiming a desert than just adding water. You need soil rich in the right nutrients
and full of organic materials and organisms. You can’t simply brew vats of micro-organisms
and mix them in with the sand, you need roots to keep everything from washing out or being
blown away. One could also use a mixture of retaining
walls and artificial fibrous materials to help further stabilize everything. Clay and biochar can be mixed into sand pulled
up from deeper down to build up a soil base. We’ve also got a new material called LNC,
Liquid Nano Clay, that has shown great facility in binding sandy and arid soil up quite quickly
and can be mass produced. We’d also most likely introduce nitrogen-fixing
bacteria, probably engineered lines that have been tailored to pull nitrogen from the atmosphere
faster and more efficiently in order to enrich the newly created soil and build a layer of
silt to bind the sand. We don’t necessarily have to go to high-tech
though. By planting bands of plants along the desert
margins or in existing oasis, you can slowly invade the desert regions so long as you can
supply them with water. Getting that water and keeping it there is
our main focus for today, but we don’t want to underestimate the soil aspect. As our ancestors found, back when they first
began experimenting with bringing water to parched lands for farming, keeping that soil
in good condition once you brought water in by canals and irrigation was just as hard
as getting the water there. It’s also a way we can experiment with terraforming
other worlds, which will need far more work than deserts. Indeed, as we often point out when folks suggest
we should abandon dreams of space colonization to focus on Earth’s problems, not only can
we walk and chew bubblegum at the same time, but we can often learn things working on one
problem that will help with another. As an example of that, we often worry about
greenhouse gases, rising water levels, decreasing biodiversity, and supplying enough food for
a growing planetary population. Soil, is a good carbon sink, and soil that’s
deeper and has a higher carbon density is more productive, more flood resistant, more
drought tolerant, and supports a more robust ecosystem. It’s not a small amount of carbon either. If you add up every kilogram of carbon located
inside plants, animals, and the atmosphere, that total is about half what’s stored in
our soil. Now soil doesn’t just store carbon, it stores
water too. Not much, relatively speaking, but every bit
counts if you’re worried about rising sea levels, and if you start making lakes and
reservoirs too, it starts to add up. This of course gets us back to water and how
we get it. We should note a few things. First, Earth’s freshwater supply is produced
by solar evaporation, and that’s actually not a very efficient way to desalinate water. We get something like 500 quadrillion liters
of rainfall on Earth every year, which sounds like a lot but we get something like 5 trillion,
trillion joules of energy from the Sun every year driving that, so in terms of efficiency
sunlight produces about 1 liter of fresh water for every 10 million joules of energy, about
3 kilowatt-hours. Most desalination processes use around that
much energy to produce a thousand times that much drinking water. Sunlight is free of course, but as channel
regulars know, in a lot of the futuristic scenarios we discuss here, your economic bottleneck
becomes waste heat removal, and it will be important here too – more on that in a bit. Second, most of that rain basically goes to
waste. The majority falls right back down on the
oceans, much of the remainder falls in places and amounts where it drains off unused by
plants, and goes right back into the oceans, often carrying critical nutrients along with
it. Even once it is in the ground and plants,
it’s often not used to efficiently, evaporating away again. Slapping a greenhouse over a location obviously
drops its water usage a lot, but so does just having a ground cover that minimizes evaporation
from the soil. So too, watering areas at the right times
of day can help retain that moisture, while doing it at the wrong time of day can not
only see a lot of it evaporate away but scorch the plants while doing it. Beads of water act like lenses, concentrating
sunlight just like a magnifying glass, not usually an issue when it’s actually raining
since the sky is cloudy, but problematic while irrigating. Third, there’s already enough water, even
on land, to green every desert on Earth, it’s just not located at the right places and times. Seasonal river flooding occurs even in areas
that are regularly drought-blighted, so if you can store it and move it, all the better. Deep reservoirs are better than wide ones,
because it means less surface area for evaporation and exposure to sunlight. We spent the last two episodes talking about
colonizing the oceans and building islands, and it’s worth remembering that if you have
a big lake acting as a reservoir, that’s also useful for other purposes as we saw in
those episodes. You can do farming in lakes, both classic
marine life and floating raft farms, which isn’t high-tech or revolutionary. After all, we’ve been doing that in Mesoamerica
for centuries. Also, while moving water horizontally is relatively
cheap compared to desalinating it, moving it vertically is more expensive. It takes about a million joules of energy
to lift a cubic meter of water every 100 meters of height and most of the Sahara, for instance,
is far higher than that. Not every arid region is high altitude of
course, but water does drain down so there is a correlation. While the energy needs for pumping would be
less than evaporative desalination, that can easily exceed our more efficient desalination
processes. If you’d like a detailed walkthrough of
desalination and pumping math for the Sahara, Real Engineering’s channel has a great episode
on Terraforming the Sahara I’ll link below, that digs into the numbers on desalination
and using forests as carbon sinks in the Sahara with current figures and technology. I should mention you can also move water around
continents, shifting it from wetter to drier areas, but don’t assume we can’t move
it between continents either. Tunnels and pipes don’t stop working just
because you hit a coastline and you could reap a net energy savings where the fresh
water source was a higher altitude than the destination. When it comes down to it, if you need to cool
some places down and warm others up water is a pretty good medium, we’ll discuss that
more in our topic for next time in the series, colonizing our arctic regions. While such a thing would require millions
of kilometers of piping, we already have million of kilometers of piping. Needless to say, approaches like that require
a lot of construction and a lot maintenance too, and while pumping water around and up
to fall down on crops isn’t too energy intensive, it still does take energy, and let’s not
forget the cost of maintaining all that infrastructure too. One technology we often discuss using on the
channel is orbital mirrors or shades, you can use them to cool a planet by blocking
some light, and you can use them to add light too. You can concentrate that a bit as well, and
mirrors are cheap and easy to make, and shades even easier. Thus, they’d be one of the easier industries
to get going on a place like the moon, saving us launch costs. They also need no structural support in orbit,
there’s no wind or gravity for that structure to resist, so they can be thin foils. Now a caveat to that is that while focusing
light down on some bit of sea, or an artificial shallow saltwater lake, will get you a lot
more evaporation, it’s also adding heat, and doubly so because water vapor is a greenhouse
gas. That’s okay though because you’re getting
enough extra bang for your buck in terms of evaporation that you can add shades to block
light to compensate. Now, we happen to be pretty amateur still
at weather modeling, especially when we’re tinkering with a system and can’t use historical
data as a reliable guidepost, but we will get better at it, and a good mix of shades
and mirrors could allow us to just tweak the existing weather patterns so rain was coming
down where we want it in the amounts we want. Less flooding, less droughts. As I said back in our power satellites episode,
I was never a big fan of beaming energy down to Earth, but that approach has really grown
on me as an alternative in case we never get commercial fusion going. It also would serve as a multi-trillion dollar
sector of our economy, one we can kickstart a serious orbital infrastructure off of. Solar mirrors and shades, which use almost
the exact same raw materials and manufacturing, complement this very well. If we coupled these with improved computing
and modeling, we could arm ourselves with powerful tools to address environmental concerns. However, you wouldn’t necessarily have to
go way up in space to accomplish this trick, a tower works just fine, and hardly needs
to be a large or tall. We’ve discussed using mushrooms habitats
in Colonizing Mercury, basically mirrors above a habitat to bounce light away, and the reverse
for farming in the asteroid Belt in Colonizing Ceres to concentrate light instead. Both could be adapted to accomplish what solar
mirrors and shades do. As would big balloons or blimps covered with
mirrors on top, akin to those we discussed in Colonizing Venus. Orbital options are better, removes all the
atmosphere issues, but harder to build too, just another reminder that the tricks we learn
for off Earth will often be adaptable to Earth and vice-versa. If you’re pumping some seawater into pools,
under glass and a lens, letting that evaporate condense on the dome and drain down the sides,
and flushing the remaining seawater back out to the seas, you get the same effect as our
orbital mirrors. For that matter, you hardly need a lens. A nice tunnel greenhouse, with a canal of
seawater down the middle and plants on the side, will get all its freshwater that way. Making all that glass, or whatever transparent
material you use, wouldn’t be cheap, but at least there is a ready supply of sand on
hand to use for construction. Of course any powerplant that uses steam as
a working fluid can also recover that water. For that matter, any manufacturing process,
like melting glass, produces a lot of waste heat that can be used for evaporation too. It would be a bit challenging to make a solar
kiln that could make glass sheeting but it’s doable and certainly solar panels or other
power sources could be used for that. If you’re using plastic, then some of those
plants can be used as a feedstock for the plastics too. Very energy intensive, not to mention labor
intensive, but it’s worth remembering that we have a lot of deserts and even just the
Sahara alone, if converted into farmland with the same production per acre of modern farms,
could grow about 12 billion tons of grain per year, about 6 times our current global
output. As we’ve mentioned before, greenhouses are
vastly more productive than open air farming, in terms of output per land area anyway, and
that would be true of ones used principally for desalinating water too. Moreover, you need not cover every bit of
land in them, since greenhouses don’t use much water themselves, you can transfer excess
water produced in them to irrigate the surrounding area. It’s also a good way to move heat from a
desalination greenhouse, they’d get awful hot on their own. You could shade one or ventilate, but it’s
far more efficient to use that water and irrigation pipes as your radiator and thermal storage
mass instead. If done properly, the temperature differential
can also power your pumping system. We’re not limited to sunlight though, if
technology keeps improving in the areas that look favorable right now. Tiny nanomaterial meshes can simply screen
salt out of water, and we may be able to scale that process up, and of course fusion seems
on the horizon and with vast amounts of energy you can run all the desalination you want,
again even modern techniques are about 1000 times more efficient than ambient sunlight
on water so if you’ve got a huge cheap power source you can just make what freshwater you
need and pump and spray it around your fields and forests exactly in the amount and times
calculated for highest efficiency. Works on normal crops too, we irrigate a lot
right now and while desalination is way more energy intensive than pumping water, the cost
of transporting water is still enough that even in places like where I live, right on
the Great Lakes, we can still have drought issues. Energy doesn’t need to get much cheaper
to end that. Cheap energy also helps a lot on producing
fertilizers, especially nitrogen compounds. But just as we’d like to use more nitrogen
fixing crops than manufactured nitrogen fertilizers, biology offers us some options for desalination
too. First off, saltwater may be harmful to most
terrestrial life, but oceanic animals and plants do just fine on it, it’s not like
seaweed and fish lack mechanisms for dealing with saltwater, quite to the contrary it’s
what everything evolved in originally and the stuff that migrated to land just lost
the ability. You could grow crops in a desert just fine
on seawater, they just need to be modified or tolerant plants. We have quite a few plants like mangroves
used to more briny and brackish conditions, near river deltas, that would contain genes
we could splice into something like corn, and there are already some salt-tolerant rice
crops. Actually we have a lot of crops that are relatively
tolerant to soil salinity, in the ancient Fertile Crescent they also had to deal with
salts building up from irrigation and found that some crops would still grow in soil whose
salinity was too high for others, and doubtless the ancestors of many of our crops got bred
from the ones that did better in salinated soil. People often worry about GMO food crops, but
it is always good to remember that most of the ‘natural’ crops we have these days
are about as natural as a Poodle is. We can modify crops to live in more saline
soil and thrive, and we’ve gotten fairly good at leaching and flushing salts out of
soil too. Of course you’re not necessarily using soil. We always talk about using hydroponics or
aquaponics in space or in vertical farming, and we could just as easily use seawater as
freshwater. You could cut canals and qanats into a desert
region, full of seawater, and cover them with glass to capture the evaporated water, use
what you need to grow crops, then mix the remaining water along with plant matter into
the sand to compost into soil. Oceanic plants might live in saltwater but
they use metabolic processes to keep intercellular salinity low. You could probably even alter a plant to overproduce
water and act as a transport, like some vine network that runs from a seawater pool or
canal to a ways away where it transpires out large quantities of fresh water vapor for
recapture and irrigation. We were talking in previous episodes about
how people like to live near coasts or river shores, and about how we might build lots
of snaky islands out into the seas to maximize this real estate. I also mentioned cutting canals into continents
to achieve a similar result, and you could do the same into deserts, just tons of canals
of seawater, evaporating freshwater that’s collected and moved to the soil nearby. And if we don’t mind building very long
and deep pipes, ones kilometers deep, We can also take advantage of the very large pressure
differential between the top and bottom of the sea to act as the pump for a reverse osmosis
filter. This requires a very long and sturdy pipe,
but we already discussed making some of those last time in Colonizing the Oceans. This gives you a very cheap way of desalinating
water and dispersing the waste brine. We also mentioned the option of going a bit
deeper and drilling boreholes right into mantle to extract heat and minerals, Moho Mining,
and how that’s easier in the oceans where the mantle is closer. You could use the steam from cooling that
magma straw or just let the boreholes act as cloud factories. Again, fusion is your best option as are desalination
techniques that don’t use evaporation, for water per unit of energy, but any time you
can get something as a free byproduct of something else anyway, that’s even better. And if you’re willing to build big enough,
tall and deep, you can get some truly mountain-like towers that get those freebies. So lots of techniques. Which ones we use in the future will depend
on tons of factors and not just those involving technological progress. If you want to pump water from the Congo or
Mississippi to the Sahara or Mojave, you don’t just have to worry about how the energy and
infrastructure maintenance costs stack up against desalination plants near those places,
but whether or not the source regions are okay with that. Rivers tends to be borders too, so getting
permission is almost always going to involve getting it from multiple entities. Small scale projects that don’t need to
bring in much exterior resources will work better in some areas, while others can more
easily engage in massive efforts both in terms of costs and geography. Water rights are traditionally a very big
deal, wars have often been fought over them and countless smaller scales disputes have
occurred and still are commonly resolved in courts even today. But there is also a lot of available fresh
water not in dispute, such as river water and glacial melt water that just flows into
the oceans. Much of this water can be redirected or pumped
to useful locations or at least retained and used locally for irrigation or brackish farming. If you’re a small farmer near the coast,
you can build a seawater greenhouse without much exterior help or permission, if you’re
inland, you can build an air well condenser, or a dew condenser, to get some water out
of the air or concentrate what comes down in the dew. Keep in mind, a place that only gets a few
centimeters of rain or dew a year, as opposed to more like the meter we’d like on good
farmland, still is getting enough water to grow a smaller portion of land. Get a plot of land and stick a house on half
of it, and all that water sloshing off the roof just doubled your effective rainfall
level. So if I roof over a section of land with a
greenhouse, or even just a sheet of plastic, the rain that would fall there will slide
over onto the other soil, concentrating that rain. In a lot of the marginal areas on the edge
of deserts, where we’re fighting desertification, you only need a little more water, so even
just partial green housing combined with some water conservation tricks like mulching would
be enough to halt that expanding desert and start pushing it back. It’s interesting in a way because as our
farming and water conservation techniques improve, these desolate areas become very
attractive as our breadbaskets. Now, they do have their own ecologies already
but as mentioned our deserts have been expanding, largely from our own activities, so pushing
those back aways seems preferable to knocking over existing forests for farmland and a lot
of the techniques needed to make them work are the ones we’re likely be implementing
in future generations to get better yields from existing croplands anyway. If you want maximum yields, you farm under
a greenhouse, it doesn’t much matter where that’s at, and you’d inevitably be supplementing
the desert ecologies nearby too allowing them higher densities of flora and fauna to replace
land lost to those ecosystems, much of which was only recently obtained anyway. We’ll see a similar factor in play when
we discuss trying to make arctic region livable in the next episode in the series, and that
will be a good deal harder too, since beyond being cold and poorly lit, they don’t get
much rain either. Albeit, they have plenty of freshwater tied
up in the ice. Speaking of that, there’s also the classic
option of towing icebergs to the deserts or pumping melt water to them. Lots of options, and lots of research going
into this area too, we only scratched the surface today. Ultimately the best approach is likely to
involve subtlety altering the weather and in a way where we can predict and select the
outcomes, using the minimum force for the maximum result, rather than brute force techniques
or trial and error. Anyone who’s seen a weather forecast knows
our predictive capability on weather is still limited but improving. When it comes to predicting weather on other
planets or inside giant artificial habitats, we’ve a lot of work to do but the basics
forces and variables are known to us. Yet it can seem a bit mysterious because discussions
of weather tend not to give the details. It can be a lot of fun trying to figure out
what the weather would be like if we created a hot zone in the Atlantic off the African
coast or inside some O’Neill Cylinder or on a flat planet, and if you’re interested
in learning how to do such things yourself or just want to better understand how the
weather or seasons work, then try out Brilliant’s course “Out in Nature”. It’s a good place to get started in learning
along with Brilliant and it covers everything from the reasons for the seasons to the Greenhouse
Effect and Coriolis Effect, from pressure systems and hurricanes to tides. If you want to increase your own understanding
of that topic or others, and have fun while you’re doing it, go to brilliant.org/IsaacArthur
and sign up for free. And also, the first 200 people that go to
that link will get 20% off the annual Premium subscription. Next week we’ll return to the Moon to look
at how things may play out as colonization proceeds and we begin getting some serious
civilizations up there, in “Battle for the Moon”, and we’ll take a look at our Book
of the Month, “Artemis”, the newest novel by Andy Weir, author of “The Martian”. The week after that we’ll go further out
in space and time to look at options like suspended animation, freezing, and stasis
for moving colonists to distant worlds, and the various ways you might operate such vessels,
in “Sleeper Ships” For alerts when those and other episodes come
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have a Great Week!