The first portal is placed at bottom-most point of the Mariana trench (the deepest part of any ocean, located in the western Pacific Ocean) and the second is placed in the Sahara desert in Africa at the point farthest from any ocean.

The second portal is inverted so the water jets directly to the ground. Each portal is 10 kilometres in diameter and stable.

Assume the system is a one way transfer, i.e. from trench to Sahara.

The portal system has zero mass transfer losses and there's no energy consumption by them or by objects pass through them. They're connecting the two points on earth in space-time. They're not affected by the altitude difference or the potential energy difference between them.

What will be the climatic changes on earth as a result of this?

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. Additionally, please keep things civil. $\endgroup$
    – HDE 226868
    Commented May 2, 2017 at 15:22
  • $\begingroup$ Mandatory related XKCD references: 1, 2. $\endgroup$
    – Trang Oul
    Commented Apr 12, 2022 at 13:39

6 Answers 6


The climate of Earth has been roughed up quite a bit last century. But it has no idea what it's got coming with this portal of yours.
Earth turns into Venus.

Update: As R.M. pointed out, the amount of energy is not 'maybe a long term thing', it's the Major Issue. This has been fixed now.

How much water are we talking?

Let's say your portal is 10km below sea level. Dropping from that pressure to pressure at sea level gives a flow speed of somewhat over 400 meters per second: $\sqrt{10^4\mathrm{m} \cdot 10 \frac{\mathrm{m}}{\mathrm{s}^2} \cdot 2}$ (water is incompressible so we can just use potential energy). This is well over the speed of sound, or comparable to the speed of a typical handgun bullet.
This 400 m/s flow is though the entire portal, $\pi \cdot 5000^2 = 7.9 \cdot 10^7 \mathrm{m}^2$, for a total of about $30 \cdot 10^9 \mathrm{m}^3$ of water per second, that's a cube of water about 3 km or 2 miles on a side per second.

Comparing that to other rivers. The discharge of your portal is about 100 000 cubic kilometers per hour, or about three times the the amount of water discharged by all of Earth's rivers in a year.

Comparing it to a lahar, a very destructive mud flow. These can be 100 meters deep and run at 'several tens of meters per second'. If the stream from your portal would turn into a lahar of 50 meters deep, it would be 2000 km wide. If we were to slow it down to a mere 40 meters per second (as fast as a car going over the speed limit), that would require it to be again 10 times as wide, so 20 000 km. Sailing around the entire African continent is only slightly more than that. So the entire African coast would turn into an extremely destructive mud flow of almost 50 m deep. Given that there are mountains to the south of the Sahara, the mud flow will probably be much deeper and mostly to the North.

At this point most of my assumptions are starting to break down. I assumed the effect on the ocean surface would not be too great. It will likely be a giant maelstrom tens or maybe even hundreds of kilometers across. This means the amount of water flowing through it is going to be somewhat less. Let's cut it by a factor 10, so $30\cdot10^8 \frac{\mathrm{m}^3}{\mathrm{s}}$.

The volume of Earth's oceans is about 1.3 billion cubic kilometers. There are about 30 million seconds in a year, so that's about 90 million cubic kilometers per year. So it takes about 15 years for the portal to cycle through the equivalent of all the water.

What happens to that water?

The specific heat of water is about $4 \frac{\mathrm{J}}{\mathrm{kg \cdot K}}$, so it takes about 4 kilojoules to heat a Liter of water 1 degree Celsius. That's about 4 MJ to heat a cubic meter 1 degree. The potential energy in dropping a cubic meter of water from 10 km up is about 100 MJ, so you're going to heat up your water about 25 degrees by slamming it high speed into the sand (or, quite quickly, other water).

This means that, if the Earth's energy loss from radiation would stay the same, in about 15 years all the water would have cycled through the portal once and the ocean would, on average, have heated up 25 degrees. Another 45 years and all the water will be boiling.

Water has a latent heat of about $2.3 \frac{\mathrm{MJ}}{\mathrm{kg}}$, or $2300 \frac{\mathrm{MJ}}{\mathrm{m}^3}$. So it then takes a few centuries for all the water to boil off and turn into vapor.

What will happen to all that energy?

Normally, the Earth radiates away energy as long wave, or infra red radiation. Greenhouse gases like carbon dioxide reflect this radiation back at us.

There is a lot of carbon dioxide stored in the oceans, around 60 times that of the pre-industrial atmosphere. However, if water is heated, it can't store as much carbon dioxide. Water of about 30 degrees Celsius can store only about a third of what water of 4 degrees can store. This is actually much more complicated than dividing by a third.

So, if all the oceans heat up 25 degrees, the carbon dioxide in the atmosphere is going to increase by factor of 10 or so. We've managed to increase it by about 50% or so in the last hundred years.

To add to this, warmer water evaporates more readily, and water vapor is also a very strong greenhouse gas.

This means that the Earth wouldn't cool nearly as fast as it normally would.

And, at some point, maybe after a few years, maybe after several decades, even if you were to turn off the portal, the increased greenhouse gases and incoming energy from the Sun will will cause a runaway greenhouse effect and turn Earth into Venus.

Who dies first?

The first creatures to die is probably a fish being blasted into an unlucky scorpion at high speed. After that anything going through the portal will die. Next to go is anything within a few hundred kilometers of the Mariana Trench and anything in Northern Africa.

Europe and the rest of Africa will soon (within hours? days? weeks?) follow. The shortest path from the Saharan portal back to the Mariana Trench is through the Himalaya's, so my guess is the water will mainly flow through Africa towards the Southern Atlantic and through Southern Europe the Eastern part of Africa and the Arabian Peninsula into the Indian Ocean. Everything in its way will die.

So the America's, most of Asia and Australia will likely not flood. Australia is closest to the Mariana Trench, so the weather there will turn weird after a day. It will take probably take a few days for the effects of the sudden change of energy distribution to be transported by the jet steam towards the America's and the remaining parts of Asia, so they've got maybe another week before the freak weather begins (think hurricanes, extreme rainfall, etc.). Some animals and some humans in those parts of the world could possibly survive this for a few years.

Some speculation on what would happen if the water didn't heat up:

The remaining flow is still a good 20 times the amount of water the Gulf Stream transports at its peak, so I would wager all ocean currents stop doing what they're doing and start flowing towards the South-West Pacific.

This means no more warm water flowing to the North Atlantic so that's a new ice age for Europe. Similar goes for Japan.

Most of North Africa is going to get flooded, I have no clue what that will do with the climate. This water is going to be under 10 degrees Celsius, so it'll cool down equatorial areas by a lot.

The giant maelstrom around the Mariana Trench is going to cause a lot of mixing in the Pacific Ocean, so most of that ocean is going to be a lot colder than it was before.

All of this cold water near the surface everywhere will mean that the Earth will radiate away much less energy and that there will be much less energy to drive atmospheric processes. The internal ocean water however will heat up on average.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ Commented May 5, 2017 at 1:15

First observation: The portals as described in the question create a perpetuum mobile. Salt water under high pressure (from the ground of the Mariana trench) wells up at some point in the Sahara desert, becoming a fine source of hydroelectric power. It will create a river of salt water that may fill up some basins and eventually reaches the sea (either the Mediterranean sea or the Atlantic Ocean). Now the water circuit is closed and the Mariana trench never runs dry.

Climatic change depends mainly on the size of the basins filled with salt water: The larger they are, the bigger the effect. The effect consists in dampening temperature extremes in the Sahara area and in a reduction of the deserted area. The desert will not go away completely; the Red Sea does not make the surrounding lands green pastures, and an inland sea in the Sahara won't do so either.

Depending on the outlet, it is possible that the stream of salt water enters a stream of sweet water (e.g. the Nile or the Niger) and actually destroys farmable land.

EDIT: Answers to comments:

  1. Fate of the Sahara: It will partially flooded, but remain the same as before for the largest part. It will have some more oases due to increased rainfall

  2. Evaporation rates: I don't have number ready, but they will be comparable to the ones of the Red Sea.

  3. The will be no equal pressure at any time. By the way the portals are designed, they act as a big pump pumping water from the Mariana trench up to some point in the Sahara dessert. This pump works forever (or until the magic driving it is revoked).

EDIT 2: I completely overlooked the enormous size of the portals. My answer is valid for much smaller portals (say, 10 m in diameter).

EDIT 2: Given the geographical location of the salt water outlet, the inland sea would probably the Lake Mega-Chad covering the Chad bassin. Its outlet is the Benue river flowing toward the Niger river.

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    $\begingroup$ @user7386: World climate will not be very impressed at all. I expect the main atmospheric circulation to remain the same as before. $\endgroup$ Commented May 2, 2017 at 16:40
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    $\begingroup$ As there can be no perpetuum mobile, the energy would have to come out of the water, meaning it would appear out of the portal at around -30°C. At a few cubic kilometers per second, the resuting iceberg will be preternatural, before it can start melting in the sahara sun. :-) $\endgroup$
    – Karl
    Commented May 2, 2017 at 20:58
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    $\begingroup$ @Karl Since there are portals with no energy consumption = perpetuum mobile exists. If you cannot use gravity change, you can use magnets. $\endgroup$
    – Jan Ivan
    Commented May 3, 2017 at 7:02
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    $\begingroup$ @Karl There IS perpetuum mobile for as long as the portals don't require any power. Perpetuum mobile may not be possible due to our current understanding of physics, but a set of portals as described in the breaks the laws of physics which stop us from attaining perpetuum mobile, resulting in a perpetuum mobile system. $\endgroup$
    – Aify
    Commented May 3, 2017 at 21:06
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    $\begingroup$ @Karl: The portal as described is a perpetuum mobile of the 1st kind. The key point is that it allows water to move with "no energy consumption" from 10km below sea level and to the sea level (2nd paragraph in the question). This is what makes if a perpetuum mobile; water will flow forever and ever from the sea level to the bottom of the Marianas Trench. $\endgroup$
    – AlexP
    Commented May 3, 2017 at 22:49

I assume you prefer a scientifically correct answer, as in the portal can't violate energy conservation.

In that case, we just can't have portals. But we can have a long tube, and lets just ignore friction inside that tube so we simulate most of the portal stuff. It does not even matter if the portaltube would end in the marianna trench. Just a few meters below the water level is enough. Actually, another option we have would be to dig a Trench.

Conviniently, parts of the sahara lie below the sea level. These parts would drain seawater, creating an inland sea.

The idea itself is not new: there is a page on wikipedia about this very topic, which came up a long time ago.

Regarding the climatic effect such inland see would have, we could only speculate. The water itself would be saltwater and could not readily be consumed for plant growth. But it would likely stabilize the temperature in the region. Having a large body of water nearby makes days cooler and nights warmer. Also, because of evaporation, more Rainfall is to be expected. The downside is that not only is the Sahara a very dry place, but additionally the Sand and Stone it is made off are really bad at storing Rainfall. It just permeates the sand and runs off. Therefore, even with more rain, it will stay a dry place. On a very long timescale it might be possible that few new Oasis would develop, and existing ones might get larger.

Regarding the lake itself, nobody knows yet if the inland lake would develop a healthy ecosystem or not. There is the case of Salton sea in which engineers accidentally flooded a basin. This obligatory XKCD comic explains the situation pretty well.

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    $\begingroup$ +1 for that XKCD what-if reference that the OP instantly brought to mind. $\endgroup$
    – CaM
    Commented May 2, 2017 at 15:02
  • $\begingroup$ Well but since this whole meta site is based on imagination and sci-fi why can't we think like that way... I read that xkcd comic before I posted my question but saharan desert and pacific ocean affect the whole climate of our planet and death valley is just small part and the tube idea is childish but a wormhole or portal idea is comparatively brings more sense. $\endgroup$
    – McGucket
    Commented May 2, 2017 at 15:09
  • $\begingroup$ See, I thought you were going to link to this XKCD comic. $\endgroup$ Commented May 2, 2017 at 15:11
  • $\begingroup$ I created a scientifically motivated answer because you initially posted on earth science SE. It is actually not very childish but just how a scientist would try to approximate wormholes. I remember it mentioning climage change initially (it still has the tag...) $\endgroup$ Commented May 2, 2017 at 15:12
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    $\begingroup$ Seems like an energy-conserving mechanism involving a wormhole should be possible - no need to resort to using a plain old tube. $\endgroup$
    – Brilliand
    Commented May 2, 2017 at 17:41

What if the portal transports not only water, but gravity? In that case, we have a proper portal that also conserves energy - a wormhole, if you will. Although this mechanism is kinder to the laws of physics, it actually has more severe effects on the ecosystem.

While water levels might not equalize instantly, gravity levels on both sides of the portal will, significantly shifting the gravitational field of the Earth. This will result in the entirety of the Earth's oceans migrating away from the Mariana Trench, toward Africa. While I haven't done the math, this will likely result in most of Africa, and parts of Europe and Asia, being submerged under the ocean.

On the other side of the globe, nations bordering the ocean will gain access to a large amount of new fertile land. There will likely be wars fought over this.

  • $\begingroup$ I don't understand.. would you mind elobarating​ a little? $\endgroup$
    – McGucket
    Commented May 2, 2017 at 18:09
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    $\begingroup$ @user7386 Gravity radiates outwards at the speed of light through the fabric of space. By creating a wormhole connecting the two points the "center of mass" of Earth shifts. (Because some things will be able to draw a line through the wormhole in the Sahara and reach that center in a shorter way than drawing it down through the crust, thus would be pulled towards the Saraha wormhole). Calculating the spacial geometry isn't pencil and napkin easy though. $\endgroup$ Commented May 2, 2017 at 18:16
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    $\begingroup$ @Draco18s following that idea, it could lead to the formation of two intersecting earths with the portals right in their center, to offset the gravitation problems. $\endgroup$ Commented May 3, 2017 at 14:11
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    $\begingroup$ While an interesting answer, this doesn't really address the question as asked, does it? The question was just about the transfer of materials. Trying to make a system like this obey the laws of physics is probably a hopeless endeavor in any case. (Though some people have made a lot of progress by relaxing their definition of what the laws of physics are. Causality? We don't need that! ;) ) $\endgroup$
    – Obie 2.0
    Commented May 3, 2017 at 17:42
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    $\begingroup$ @antipattern - Of course it not scientific. I know this very well, being a physicist. If, in my current model of intermolecular forces, the energy changed discontinuously, I would toss it out as flawed. Thing is, this is fiction. There is no problem with discontinuous forces, or straight up magic. Also, the energy is infinite, sure, but the power is limited (which is really the more important thing). Unlimited power is a flaw even in fantasy: it tends to instantaneously destroy your system. Unlimited energy could have next to no effect over a billion years, depending on its power. $\endgroup$
    – Obie 2.0
    Commented May 4, 2017 at 2:25

Having specified that the 2nd portal is selected for maximum distance from the ocean(s), this puts the location near the southern edge of the Sahara, probably somewhere in western Niger or eastern Chad.

The first thing to realize is that the flow rate out of the portal will be enormous. Pressure differential across the portal surface will be on the order of 1000 atmospheres. Even if the portal appears at ground level, the surface sand will be explosively scoured away right down to bedrock. I can't find a number for the sand depth in that area, but the average depth of the Sahara is asserted to be 150 to 200 feet. Let's go with 100 feet, or 30 meters. Then the total exit area will be 10 km x pi x 30 m, or about 1 million square meters. Modelling this as a circular orifice with a diameter of about 1000 meters, a simplistic calculation of flow rate runs something like 5 x 10^11 m^3 per hour. For comparison, Lake Erie has a total volume of about 4.8 x 10^11 m^3. So that will be whole lot of water.

In the short run a large lake will form, but I doubt it will last. Without knowing the subsurface topology, one can only assume that there exists the channel of a buried south-flowing river. The accumulation of water, when it finds such an outlet to the Atlantic, is likely to produce extremely rapid excavation along any such channel. The result will be a relatively narrow, very fast and deep river flowing through a terrain something like the Channeled Scablands of Washington state. The river will presumably run southward to the Atlantic. Note that formation of the Channeled Scablands required the draining of a glacial lake with a volume of about 2000 km^3 and this is about 4 hours accumulation from the portal.

Assuming that such a drain limits the area of the headwater lake, climatic effects will be fairly small. The total area of water available for evaporation will be fairly small. Furthermore, since the water is exiting at a temperature near zero Centigrade, evaporation will be further inhibited.

  • $\begingroup$ What if the portal is facing the output to the sky? $\endgroup$
    – McGucket
    Commented May 2, 2017 at 16:59
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    $\begingroup$ @user7386 - You get the most amazing fountain rather than a hole to bedrock. Everything else stays the same. $\endgroup$ Commented May 2, 2017 at 17:02
  • $\begingroup$ Hahaha we don't have to worry if any evil man tries to do this right?😂😅 $\endgroup$
    – McGucket
    Commented May 2, 2017 at 17:07
  • $\begingroup$ Good answer. About the pressure of a 1000 atm: This pressure is only existing in the first few moments, because the Water column above the portal will be rapidly sinking. Long-Term this setup will cause a massive river where all the water flows from sahara trench towards the marianna trench. $\endgroup$ Commented May 3, 2017 at 9:07
  • $\begingroup$ @antipattern - At 500 km^3 per hour, and an ocean area of 360 million km^2, the rate of sea level drop will be imperceptible. $\endgroup$ Commented May 3, 2017 at 12:57

The physics at a macroscopic scale

Your concerns about the actual water shifting around the Earth is quite reasonable. However, I can actually tell you a far worse (in fact cataclysmic) reaction that will result from you initiating connections like this that merely have downward facing openings, sit at the same elevation, and do not even suck in any water (unless it happens as a result of what I'm going to tell you).

Simply put, depending on your theory of portals and doorways in space and such, the issue is the gravity of Earth itself acting upon Earth itself. Now I'm going to actually run some numbers on this. First off we see can by googling what the actual the latitude and longitude of the placing you seek to place portals at is:



Using spherical coordinates we can obtain vectors representing the directions of each of these. This will make more sense once I move into the actual physics equations. I am presuming here that elevation is irrelevant in the sense that we only care about the direction and not the magnitude, which is what we will want farther down.

Sahara_vector = <0.3582064616, 0.1721067799, 0.9176422981>

Trench_vector = <-0.24186511, 0.1855896263, 0.9523957996>

Now that we have these we wish to construct three equations to determine the acceleration of the Earth due to itself. This means we need to construct force equations for each of the x,y, and z coordinates. There's probably an easier way but this is what I know how to do.

Now the force due to gravity on Earth at sea level is defined as "mg", where m is the mass of the object being pulled and g is the constant of Earth's gravity.

Therefore, each of the vectors must have a magnitude of mg (essentially just multiply the vectors by mg component-wise).

Newton's second law tells us that the sum of all the forces along a particular axis adds up to the acceleration times the mass. Therefore, we can now construct the following three equations:

$ma_x = mg(0.3582064616 - 0.24186511)$

$ma_y = mg(0.1721067799 + 0.1855896263)$

$ma_z = mg(0.9176422981 + 0.9523957996)$

Dividing both sides of each equation by $m$ and reducing we get the following:

$a_x = 1.141308659196$

$a_y = 3.509001744822$

$a_z = 18.345073738437$

Now, using the Pythagorean Theorem in space we can compute the magnitude of this acceleration upon the Earth.

$A = \sqrt{(1.141308659196)^2 + (3.509001744822)^2 + (18.345073738437)^2} = 18.712493397979075807350637045717$

This means that there in some direction somewhat pointing between the Sahara Desert and the Marianna Trench that the Earth will begin to accelerate towards at 18.712 meters per second squared!

(note: this might not actually be the correct way to find the magnitude but regardless the components still support my conclusion below)

Macroscopic Conclusion

Total annihilation of the planet, which makes sense given that the acceleration of the Earth is normally only 0.005954 meters per second squared. And do not expect your 'starship Earth' to be even remotely steerable. The Earth spins, regardless of the Sun. If you want to stop that, you're gonna need to turn your portals sideways and hope you get gravity going through them (likely not) to produce torque. So, everyone on Earth is either gonna get really cold or really hot pretty quick. If anyone does survive somehow due to this monstrosity actually coming back into a stable survivable orbit (which is unlikely), they can admire the new scenery which is pretty lackluster in a disaster sense.

The physics at a regular scale

Simply put, your portals are gonna clog. If the gravity of the Earth is sucking through seawater, guess what: it's gonna suck through just as much sand. You know what you get when you put seawater and lots of sand together. You get mud. Eventually, the ground is gonna rise in the Saraha and the ground will become rock hard. If it is fast enough, you'll get a weird looking mesa or a mountain. Other than that, the portal is gonna become a bottleneck and only so much can fit through. The gravitational effects will occur all over the place. Might even be regions that have 0 G's as a result. I'm not that fine tuned to locate those. But in the end, the portal will become the equivalent of your sink when you pour tons of dirt down it. Be glad it needs a plumber. The hurricanes and vortexes described in the other answers sound down right evil.

Another thing to keep in mind as well is that the portal itself might have 0 G gravity at it's opening due to the Earth cancelling itself out at that exact point, so chances are the two sides will meet and just kind of awkwardly float up there and not really do much. It might be really damaging when they first open and they slam together, but probably no worse than your average tsunami or desert earthquake. Simply put, the damage isn't caused by the moving of sand and water. It's the moving of the Earth itself that is the real danger.

In conclusion

You've created some intriguing looking geological features at the expense of every person and animal on the planet. You haven't just created storms and earthquakes. You've destabilized the Earth's orbit. Congratulations, you've created single most deadliest example of an extinction event to ever strike the Earth (if it even stays in one piece).

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    $\begingroup$ Sounds...unsustainable. $\endgroup$ Commented May 4, 2017 at 22:44
  • $\begingroup$ @antipattern Well this is assuming the things that the author put forth in their post, which are that the portals are opened somewhere above or in those regions and they remain fixed relative to the Earth. I do not know how these portals are being generated but to be frank, it would surprise me if a few hours or even a few days of these resulted in the Earth falling out of orbit. So, all it really takes is whatever mcguffin the asker intended to keep working long enough for total annihilation. I agree though. A rip in space-time shouldn't be mobile, but then we'd just have... spacial glue. $\endgroup$
    – user64742
    Commented May 4, 2017 at 23:44
  • $\begingroup$ @TheGreatDuck hey wait I've some doubts , you're saying that water coming out of Sahara will cause the mayhem in gravity and acceleration? $\endgroup$
    – McGucket
    Commented May 5, 2017 at 21:55
  • $\begingroup$ @McGucket No. Of course not. If you open a doorway in space you have to accept the fact that gravity will be able to pull things through each side. Hence, the Earth will impart gravitational force upon itself due to it being sent through the wormhole. I'll make a diagram perhaps and show you. A bit busy at the moment. $\endgroup$
    – user64742
    Commented May 5, 2017 at 23:36
  • $\begingroup$ @McGucket do you understand? $\endgroup$
    – user64742
    Commented May 6, 2017 at 2:39

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