# How to desiccate your world?

Only few millions of people survived, they are struggling to stay alive. Food is hard to find and plants do not grow (mostly). Water cannot be found on surface, the only way to get it is to find an underground river/lake.

The world is hot, dry, there are almost no clouds and rain is replaced by dust storms. After years, there are no oceans, only salt deserts.

Q: What event/series of events could possibly cause this environment?

The cause should:

• Not kill most of the people - people should starve to death or kill each other for food
• Kill most of the flora
• Make the planet hotter and dry
• Generate no radiation or contamination of food/water
• Be plausible as today. No near-future and no magic.
• BONUS: on areas directly exposed to the sun: burn the skin, causing burns on exposed parts. (This is totally optional)

Possible cause:

My initial thought was some kind of pathogen agent that kills most of the flora, but I really don't know if it would cause earth to become an almost desert world.

I also considered a Coronal Mass Ejection, but I don't like the fact that it would kill a lot of people and could contaminate water/food. I'd like a slow apocalypse.

Edit: Heat, dust, no water... this is what the outcome should be, not how the process should behave. You could just frezee the entire world if you can explain that, after an Ice age, the earth would be an almost desert world.

• Not on this Earth. Earth has just about the same amount of water it always had (for suitably chosen values of "always"). It is very hard to get rid of the water. Warmth actually helps the hydrological cycle; you may consider plunging Earth into a deep freeze. Dec 19, 2016 at 11:55
• We definitely can't remove the oceans whilst making it hotter. You can have less fresh water if you raise the sea level. Dec 19, 2016 at 11:57
• Heat is the wrong tack. You might get more water in the atmosphere, but the water doesn't actually go anywhere. The best way to actually get rid of the water would be through some cataclysm that drastically reduces the planet's mass or otherwise throws the gravitational equilibrium into disarray. So science-experiment gone awry, perhaps? Or impact with a very large meteor (or medium-sizded moon)? Dec 19, 2016 at 13:03
• Dec 19, 2016 at 14:30
• Most obvious cause is a Trump presidency. Dec 19, 2016 at 22:20

I would go with the pathogen idea. The more plants the pathogen, or pathogens, kill the better but at least the grasses and trees must die. Grasses and trees trap water and soil. Remove these and the next rain washes away any soil preventing food growth. In a drought period grasses store water underground so animals can survive by eating grass. Kill grass and water storage goes. You heard of the dustbowl in 1930s America? That was caused by killing the grasses. By removing grasses and trees you will make much of the Deep South into a desert. In fact, most of the sub-tropical zone will probably become desert. (Climate zones shown on the image below.)

Removing trees will also create problems in the tropical and temperate zones. These areas are dominated by forest. In the tropical zone, which is mostly rainforest, the death of the trees will cause all the top soil to wash away. Rainforest soil has practically no nutrients below the top layer so most plant life here will be destroyed. Losing the rainforest will rapidly increase global warming so temperatures will increase a lot giving you your higher global temperatures. Less trees will also reduce river lag times increasing flooding and, since most cities lie on rivers in the temperate zone, a lot of the worlds large cities may have to be abandoned.

Even the poplar region won't be safe. Killing trees increases global warming and will melt the sea ice so bad news for polar bears. This will increase sea levels driving people inland and destroying some food growing areas.

The apocalypse will kill some people straight away in floods and dust storms but most people will survive the initial consequences and live on, slowly starving to death under the hot sun watching the nutrient poor soil blow away in the scorching winds. At least they will have clean-ish water though.

• This would not force people to live underground, though, and use subterranean water catchments. The clean water on the surface could be managed by people and used for stable agriculture (via building and landscape architecture) Dec 20, 2016 at 17:32
• @NewAlexandria I suspect a lot of the world would move underground to avoid the dust storms and washed away soil that is making it hard to breathe and clogging up water supplies. Dec 20, 2016 at 17:34
• Pragmatically speaking, the engineering challenges of living in surface-based protected environments outweighs the physiological, mental, and toxicology challenges of living underground for extended durations (or generations). Dec 21, 2016 at 16:30
• It doesn't actually say they should live underground though. Just that all clean water should be underground. Dec 21, 2016 at 16:44
• "At least they will have clean-ish water though" Surface water in the above scenario wouldn't be toxic unless there was a local geological issue (e.g. arsenic). I'm only emphasizing this if a GM/designer has any chance to be called out on accuracy. Surface water would exist, coming in torrents, and maybe in some places more than others — i.e. water kingdoms. Dec 21, 2016 at 20:49

# By making it cold

The colder it gets, the drier it gets.

OK so this isn't strictly what you wanted, but the driest periods the planet has experienced were the ice ages. The colder you make it the more of the water ends up locked into the ice caps. Sea levels drop by hundreds of meters, the ice expands down into the temperate regions.

It's much easier to remove the water from circulation with cold than heat, Snowball Earth is surprisingly dry.

# Hotter and drier

You can make the land drier by making the planet hotter, however the ultimate outcome of this is to make the sea levels rise rather than fall. You can get to a dust-bowl scenario on land reasonably easily this way. Inland seas and lakes would be lost but you would still get fertile regions in the more temperate zones and on coasts. To get rid of the water on a hot Earth you have to make it go somewhere. This leaves you only with the Sandworm option or similar, i.e. "A wizard did it".

# Both

Go through a phase where it's hot enough to dustbowl the land, then drop the temperatures to ice age and freeze out the oceans. You'll probably kill everyone and everything this way. Internet research says that ice ages can cut in very quickly, but all the sources I've seen are questionable.

• Internet research says that ice ages can cut in very quickly Look at the documentary titled The Day After Tomorrow which documents an ice-age taking effect within days/weeks. It shows global warming melting global icebergs, breaking the global weather cycle - thus leading to a catastrophic iceage. Dec 19, 2016 at 23:29
• Well, you can lock the water up in ringwoodite or some similar crystal structure. The planet is getting hotter anyway, so the two need not be related, but this is a feasible solution to "it has to go somewhere". This could begin happening due to some massive upheaval of the mantle in the mid-Pacific, allowing the trapping of water in some crystallization of cooling minerals. Dec 19, 2016 at 23:38
• Ummmm..."The Day After Tomorrow" is not what I'd call a scientific documentary which presents information from a careful survey of well-accepted scientific conclusions. More like "a ridiculous over-blown Hollywood disaster-fest based on cursory reading of 'People' magazine, at best". Dec 19, 2016 at 23:44

Introduce sandworms.

Sorry for spoiler tag, but if you haven't read Dune saga, I don't want to spoil it for you.

Sandworms had a stage in their lifecycle when they acquired water and trapped it in the underground spice melange masses. They were the main reason for sand, for dry Arrakis. There was enough water on Arrakis for it to have Earth-like environment. In the Chapterhouse: Dune the process of drying out a planet is shown with all it's details.

If you can introduce a life form that would trap water and not release it, you could dry out the planet surface pretty well. Dry planet would probably appear hotter, too. Or at least have higher temperature variation, with hotter days and colder nights. Plants would die, and thus would no longer stop the ground from being eroded. Oceans would get shallower and more salty. Looks like this will fulfill all your points pretty well. Only... It'd be somehow derivative.

Of course, it doesn't have to be a literal sandworm. Any organism that hoards water and creates cysts in hard to reach places would do. Especially if it'll render water poisonous, thus preventing roots to suck it back out. Creating such organism might be possible. At least I don't see it less feasible than pathogen able to kill all flora but leaving fauna intact.

• Also pretty improbable. The issue being that the creature in question has to reach an equilibrium point with it's surroundings. If they consume all the water then either they're going to run out of water and start dying off, thus releasing the water again or they don't need the water at all in the first place, in which case why do they absorb it? Always bugged me about Dune, that. Dec 19, 2016 at 10:46
• @JoeBloggs all this was explained in Dune and in Chapterhouse. Simple analogy: all newborns can digest casein, many adults cannot. Baby sandworms can use water and need it, adult ones can't. Dec 19, 2016 at 10:47
• @Mołot This kinda seems like magic? Dec 19, 2016 at 10:51
• Pathogen able to kill all the flora isn't, either, and was considered by OP, so why is that an issue? Dec 19, 2016 at 11:05
• A water-hungry organism could do the job. Even if it doesn't exist now, it could be plausible in an alternate history(close to reality) so this answer is not bad at all. Dec 19, 2016 at 11:18

I would go with "electric wind", which is what's currently being cited as the cause of Venus's desiccation. In essence, strongly charged electrical wind in the upper atmosphere performed an electrolytic separation of atmospheric water, and drove the ionized oxygen and hydrogen off into space. On Earth, you could imagine this process interrupting the hydrological cycle, preventing or drastically curtailing rainfall. It's not realistic to truly desiccate a planet on non-geological time scales, but if you prevent rain from falling, you'd effectively kill off any land-based plant life.

If you wanted, you could say it was kicked off by a massive solar storm (CME) hitting Earth and charging the atmosphere, which you could also use for your bonus objective of burning those in direct sunlight - this one had enough UV radiation to decimate the ozone layer, and the electric wind phenomenon that it started keeps new ozone from forming in the upper atmosphere, so now people get sunburns and eventually develop skin cancers from prolonged epxosure to direct sunlight. CMEs are not actually deadly to people as you seem to think, based on the comment in your question, and we have historical records of being hit by some pretty big ones, most notably in 1859. People did fine, electrical equipment, however, did not.

• Dissociating the hydrogen and oxygen and letting the hydrogen be ripped off by solar wind is the only way to permanently get rid of the water. Dec 19, 2016 at 22:32
• I'll go with the pathogen idea and this one. If I could accept both answers I would. Thank you ;) Dec 20, 2016 at 8:10

What you are describing will actually happen to Earth, but your characters will need to be incredibly patient, since this is projected to happen about one billion years in the future.

As the Sun burns through it's hydrogen fuel, more and more "helium ash" accumulates in the core. The helium will not fuse under present conditions, so the radiative pressure from the core gradually decreases while the gravitational pressure remains constant. The sun's core is squeezed with increasing pressure and the rate of fusion also increases at a slow but steady amount, increasing the radiative output of the Sun (to maintain equilibrium). The Sun is thought to have increased in brightness by up to 30% since the birth of the Solar System.

The ever increasing heat energy reaching the Earth increases evaporation, and gradually the atmosphere becomes saturated with moisture. By 1,000,000,000 AD, the Stratosphere is saturated with moisture, and then an irreversible chain reaction takes place. High energy ultraviolet radiation striking the atmosphere starts striking the water molecules at high altitude, breaking the water apart into hydrogen and oxygen. Hydrogen is such a light gas that the extra energy imparted by the breaking of water molecules will allow it to achieve escape velocity, and leave the Earth's atmosphere for good. Since the heat output of the sun is continually filing the atmosphere with water vapour, this process will continue unimpeded, while the hydrosphere gradually evaporates.

This process includes other strange effects, such as CO2 leaving the atmosphere in @ 500 million years as the carbon cycle is interrupted and plant life becoming extinct, but even then, we are looking so far in the future that post humans will have evolved into post-post humans, and perhaps have developed some sort of mega engineering like Star Lifting or moving planets around to deal with issues like this.

Since I can assume you want this to happen now, rather than 500 MY from now, you will need to find a way to accelerate the Suns stellar evolution or artificially increase the Sun's output. Since the rate of fusion inside a star is moderated by the mass of the star (larger stars have more mass and are therefore hotter), you either need to dump trillions of tons of mass into the star (more than the current mass of the Solar System), or do something like dropping a neutron star or mini black hole into the Sun's core to "pull" more mass into the core. How this happens is an exercise for the reader.

Alien invasion

About a hundred years ago tens of thousands of Monoliths descended. They can't be scratched or dented, they appear to be smooth black oblongs with dimensions that scale according to the cosmic 4 sequence. After a while scientists realised that the Monoliths had a peculiar property: They seemed to attract atmospheric H20 and, through functions unknown, capture it. Once some unknown criteria is met the Monoliths rise and depart our planet and new ones descend. A constant stream of Monoliths are now entering and leaving Earth's atmosphere, each stealing some precious water as they go. Nobody is sure why the Monoliths were sent, but the effect is undeniable:

Slowly but surely all the water on Earth is being removed.

If the space above the monolith is covered for any reason the monolith will slowly and inexorably rise, pushing all before it, and a replacement monolith descends elsewhere. As the sun continues to make water evaporate and the Monoliths continue to capture it humanity is becoming more desperate, enclosing the last water stores in closed-systems deep beneath the earth. Plants can be grown in hermetically sealed domes, but as the global average humidity continues to drop all but the most hardy plant and animal life is beginning to die off, and the Monoliths have started to land in increasing numbers nearer and nearer to the domes.

We don't know why this started, or if it will stop, but we do know that this thirst will kill us.

• Disclaimer: Monoliths may not be an original idea. Dec 19, 2016 at 11:20
• I really like this idea, and, even if it's not what I was looking for, I still appreciate it. Dec 19, 2016 at 13:16

Within a few year (decades or centuries) it is virtually impossible due to the really HUGE amount of water stored in the oceans.

Human activity can do the trick: Imagine a hydrogen based economy (with hydrogen powered cars, ships, planes etc.) on a really big scale that looses permanently some hydrogen to the atmosphere and finally to interplanetary space. This can do it, but we need to consume much more energy than we do today ... and humans will notice the falling sea level hopefully soon enough to change their economy!

Without worrying too much about physical mechanics:

• You could postulate a world where [some massive mantle-cracking geological trauma] has caused rifts in the earth's plates, and other fissuring — which has allow the oceans and groundwater to largely 'drain' into the layers of the earth.

A few advantages to this mostly-imaginary physics:

1. It could happen fast: Quirk of the earth's core rotation. A celestial event. Etc.
2. Draining/absorbing of the oceans would take a while, and allow the slow-death / adaptation you mention.
3. It would enable you to have a wealth of 'new world' events that players wouldn't presume:
• All the water in the mantle has to change, eventually. There's too much heat for it to remain there forever.
• random deep-earth catchments could be discovered. Empires built on access to secret caches
• Geysers of mythological proportions could occur suddenly. The watery equivalent of volcanos.
• New forms of earthquakes would occur. These tremors could be more electrical / geo-magnetic, since the earth has more layers of water in it now (which is a dielectric, like an electrical battery).
• so, think earthquakes that cause electrical storms; change animal migration patterns; cause earth-light phenomenon; blackouts and other cognitive / perceptual changes in people & animals
• the now dry lakes, seas, and oceans are likely candidates for deep-earth movements of water, which cause huge sinkholes of sand, perhaps so expansive that they are like sand-rivers.
• all of it can culminate in a world-breaking rebirth event, where the waters return to the surface. Can be as epic (sudden in time) or long & drawn-out as needed.

Seems like fun times full of mythological heights.

• Some people think this actually happened - Google catastrophic plate tectonics. If the geysers hit high enough in the stratosphere they could generate enough electricity to create their own electric wind as described above and lose the hydrogen to space while leaving the remaining atmosphere relatively intact. Dec 19, 2016 at 22:41
• I hadn't heard of it. It's a nice footnote, so thanks, but I think (out of the catastrophe models / physics, Immanuel Velikovsky's work is the most compelling. Dec 20, 2016 at 17:27

It is going to happen in Earth in about a billion years: Runaway greenhouse effect. Increased Sun activity will cause more water to evaporate until greenhouse effect caused by water vapor will increase temperature to a point where oceans will boil.

The problem with this scenario is that it will get too hot for your purpose - several hundreds of degrees - and humans won't be able to live like in a desert. It will be more like an oven or a furnace than a desert.

And if you don't want to wait a billion years, you can trigger runaway greenhouse effect by building up huge amounts of greenhouse gases in the atmosphere to raise temperatures a few tens of degrees and water vapor will complete the work.

## The thing standing between the Earth as we know it and your apocalyptic wasteland is the Earth's magnetic field.

The Earth contains a spinning nickel core that interacts electromagnetically, this redirects charged particles and hinders radiation. Were you to weaken this process somehow, possibly by stopping the Earth's rotation, you could cause the field to weaken. When a planet has a weak magnetic field it is no longer shielded against the electromagnetic radiation put off by stars near it.

Take for instance, Mercury. Mercury has very little atmosphere in part because it lacks a magnetic field, this means the solar radiation is intense enough to strip off any gas or water vapor as well as heat the surface enough to boil liquids.

The potential scenario could be that the Earth ceases to spin, at once or over time, (so 1 day = 1 year). In this scenario the Earth's oceans and atmosphere would gradually be stripped away by radiation leaving behind a half radioactive oven, half sunless icebox with little or no breathable atmosphere.

The other potential scenario involves not eliminating Earth's protection, but rather increasing the strength of the radiation and charged particles it repels. If the Sun became more powerful, which it eventually will, a similar process would occur.

You can choose how advanced this process would be, you'll have to choose a time during which the atmosphere and some surface water still exists to some extent, and radiation and lack of atmosphere is intense enough to kill without protective clothing and provisions but not enough to be completely uninhabitable (like the surface of Mercury) without lots of expensive equipment.

You could also offset the Earth's orbit. If you skewed it a bit, it could get closer to the Sun, but only temporarily. This would not be drastic enough realistically, but it is a powerful climate change mechanism. Regular oscillation in the Earth's orbit is the principal cause of ice ages. Moving the Earth closer to the sun is a plausible idea though.

Collapse the planetary magnetic field.

Collapsing the magnetic field also ends the magnetosphere / Van Allen belts. Those protect the upper atmosphere from erosion. Over time, the atmosphere will lose pressure. Liquid water will evaporate and this will have a short term compensating effect, but eventually you will be left with a very thin atmosphere and no water.

For an actual example of this process, see Mars.

• It'll still take a good few hundreds of millions of years for all Earth's oceans to be lost into space. This is fortunate, because the Earth's magnetic field does fade for brief periods between pole reversals, which happen somewhat regularly every few hundred thousand years. Dec 19, 2016 at 18:10

Giant Space Tree! In this novella Niven posits

a spacefaring lifeform which shoots seeds across interstellar voids sucking up all of the water on a planet before launching new seeds out and perpetuating its lifecycle. One has already gotten Mars, and Earth is next.

Niven's take on the concept is rather absurdist. That whole collection of short stories has a humorous bent to it. The central idea of that particular short story is pretty intriguing though, and a serious take on it might yield interesting results.

The most plausible cause for all of that to happen is Earth gets closer to the Sun. Only 1 inch closer will be enough. You could make a scenario where some object(asteroid) hits the Earth and Earth gets closer to the Sun. All the things mentioned above would happen as a consequence of this event.

• An asteroid fast enough to change the Earth's orbit would kill everybody on the planet ( if not everybody, at least 90% of human population.. ) Dec 22, 2016 at 17:16

Ozone strippers, dump enough CFCs into the upper atmosphere and the UV that punches through will kill most of the life on Earth, the added UV will also destroy water molecules reasonably rapidly, the hydrogen escapes the atmosphere and the oxygen decomposes the dead Carbon and Nitrogen from the land causing runaway warming as nitrous and carbon oxides build up, the end result looks a lot like Venus as eventually the oxygen runs out of carbon and starts to oxidise sulfur from the land surface and the gas pressure just goes up and up.