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First of all, I'd like to make a disclaimer, and that is that I'm in a brainstorming phase as of now so this question will be generally vague. This also means that any ideas you're willing to propose are very welcome. Consider this as a semi-blank canvas

Now, I'm currently working on a planet very similar to Earth (which I'll just call Planet X for convenience): same day & year length, is in the Goldilocks zone of its host star etc. Life on Planet X evolved much like on Earth and the sapient humanoid species inhabiting it possesses a level of technology very similar to ours.

Suddenly, something happens that makes the temperature rapidly rise to unsustainable levels forcing these humanoids to live underground.

What I'm looking for is a way to make Planet X rapidly turn into a scorching wasteland, and by rapidly I mean preferably in less than a century.

So far I thought of the following method: somehow the orbit is altered, becoming more eccentric, causing the planet to get dangerously close to its star during perihelion. If possible, I'd like to make it so that their winter isn't colder than our springs or falls at best (a medium temperature of 23-ish degrees celsius at least on the equator would be ideal) while their summers are a true scorching hell (I was thinking something along the lines of 100-130 degrees celsius at least on the equator). Let's assume Planet X has an extremely negligible axial tilt as well, almost non existant

If we went for this approach...

1) What could possibly make Planet X's orbit more eccentric in such a short timespan (less than a century)?

2) Since X would get very close to its star during perihelion, would the surface become heavily irradiated? If yes, could not only the surface but also the underground become radioactive? If yes, up to what depths?

3) In the unlikely case radiation wouldn't be a problem, would these humanoids be able to even live on the surface during this spring-temperated winter I mentioned earlier with no side effects?

4) Would at least the poles of an Earth-analog withstanding such heat be spared from desertification even during or after summers with peak temperatures of 130 degrees celsius on the equator? If you deem the temperatures I proposed too extreme, feel free to adjust them in a way you think it'd work better

Alternatively, for Planet X to rapidly become a scorching wasteland we could make it orbit a red dwarf. I heard they're unstable stars that can emit unpredictable bursts of energy but I don't like the tidal lock thing and would like to avoid it... I would like your input on this as well. That is if you don't mind of course!

That should be all, I think. Feel free to propose other ways to make an Eart-analog turn into a scorching wasteland or to let me know of things I might haven't considered that you think I should be aware of. I'm all ears

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  • $\begingroup$ First, I see four different questions here. I would suggest limiting yourself to question #1 and saving the others for follow-up questions. Second, keep in mind that 100 C is the temperature at which water boils at 1 atm. I'm fairly certain humans don't survive long when two-thirds of their body is undergoing a phase change. $\endgroup$ – Frostfyre Oct 2 '16 at 3:32
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If you want to turn a planet into scorching wasteland without killing all the humans on it, a sudden orbital change is not what you would want to invest in. Orbital changes of the severity you have mentioned, will wipe out almost all life on the planet probably within a year or so. Considering that getting closer to the host star would mean geometrically greater amount of solar wind, the atmosphere would be swept off quickly (as in, the effects would be felt within a couple of decades) and the destruction of almost all occupations (as the surface is rendered inhospitable) would create government collapse all over the globe, leading to a very quick and violent end of the human (or humanoid) race(s).

The strategy I would suggest for your desired scenario is runaway global warming. Once the temperature of a planet reaches a certain tipping point (depending on the environment of the planet), it would start a cycle where more of the sunlight is absorbed, causing the atmosphere to heat up more, releasing more of the greenhouse agent, absorbing yet more sunlight and so on, until all of the greenhouse agent has been released and a new stable temperature has been reached.

The greenhouse agents worth considering for triggering the effect would be methane and sulfur dioxide. While carbon dioxide is good at absorbing and retaining heat, it is no match for monsters like methane and sulfur dioxide. Once the tipping point temperature is reached, the evaporation from oceans will increase uncontrollably, leading to an ever increasing amount of water vapor in the atmosphere ... and water vapor is the monster when it comes to greenhouse effect. Once this point is reached, the oceans will boil away, rendering Earth a blistering hot, dead planet.

And as Frostfyre has specified, forget any complex life for temperatures above 80 °C. Humans would already go extinct once the global temperatures reach or exceed 55 °C. The swift change would not allow for constructing underground habitations as a lot of the people involved in designing and managing the construction process would be already killed by the heat. Also, humans forced to live without sunlight for extended periods of time get emaciated and slowly waste away.

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I hate to be cynical, but the easiest way is for us to continue what we are already doing: enter image description here

in this image, the dotted line is the temperature trend and the central line is the 1960's temperature average, with every other straight line being a degree Celsius difference

Just keep burning coal and we will kill all plants and animals, then you have your barren wasteland

Source: http://xkcd.com/1732/

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  • $\begingroup$ While global temperatures surely are rising, there is only so much coal and oil. If we burned ALL currenly known coal and oil reserves in the next 200 years, we would increase CO2 to about 2000 ppm (use the 5000 GtC line for current estimated reserves). That is similar to the CO2 levels in the Mesozoic. While not ideal for humans, Mesozoic conditions are certainly not unfit for life, or even particularly dry. $\endgroup$ – kingledion Oct 3 '16 at 2:10
  • $\begingroup$ @kingledion it's not the CO2 that kills us, well not directly, CO2 means global warming and its that which kills all plants, therefore all animals $\endgroup$ – Alex Robinson Oct 3 '16 at 7:18
  • $\begingroup$ I agree, and what I'm saying is that global warming will top out around 8-10 degrees C, which, while toasty for mammals, won't be too hot for dinosaurs or their modern day descendants (birds), won't be too hot for reptiles in general, and most importantly, won't remove the water from the earth's biosphere. A Global warming overkill Earth would be hot and wet from the equator to the poles; hardly a barren wasteland. $\endgroup$ – kingledion Oct 3 '16 at 13:29
  • $\begingroup$ @kingledion if you say global warming of 8-10 degrees C isn't that much of a problem, then how come it is just about the single largest issue of our century, if we can cope with this 8-10 degrees C why are we spending billions on alternate energy? its because it causes climate change, flooding, lack in biodiversity, kills off plants and then you have a problem $\endgroup$ – Alex Robinson Oct 3 '16 at 16:33
  • $\begingroup$ Its a problem for us humans, its not a problem for the biosphere as a whole. Komodo dragons and army ants and rubber trees and things that like it hot and wet would love it. Just imagine global warming as a fever designed to get rid of the human infection, not to kill the whole body. $\endgroup$ – kingledion Oct 3 '16 at 16:46
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enter image description hereBilliard balls solve the problem quickly. The cosmos is filled (meaning not completely missing) with high speed hunks of rock. You hit the planet with a rock.

With a big rock, you can have a catastrophic effect on the rotational speed of the planet. A 300 hour day would give you scorching deserts followed by frozen nights. You might get a migratory bird swarm across the evening terminator, riding the (22K/300) 220 mph winds in the habitable bands and trying to eat bugs. You might a few survivors hunkering down between the extremes and generating power for the differential. Still, no longer prime real estate.

Alternately, you can pick a number of other billiard balls for faster or slower death. Something small, fast, and dense could open a tectonic rift causing endless earthquakes, the slow loss of land, and a moderate speed release of carbon into the atmosphere. You could posit a bell-ringing shock that releases undersea or underground carbon reserves, e.g., the 'super-frak effect'. Runaway processes then take the planet to the new equilibrium.

Moving from billiard balls, a voracious mono-culture flora or fauna could take over. All the pollinators could die. Some toxic substance could kill the current flora and fauna. Endless storms. Solar flares. Passing through a protostar. Low gravity allowing vapor to escape. Aliens steal the oceans. Loss of magnetic poles. Muppets. It is a lot harder to save or terraform a planet than to destroy one.

All suggestions for fictional planets only. Not be used on inhabited planets. Attempts to terraform is a federal crime in the United States and areas under United Nations jurisdiction.

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  • $\begingroup$ An impact of that power would kill the humans (and just about everything else, also.) $\endgroup$ – Loren Pechtel Oct 23 '17 at 0:44
  • $\begingroup$ Yes. If it were to fail to kill the humans then move towards causing a serious (nova) level event because it would show that those buggers are TOUGH! $\endgroup$ – Charles Merriam Oct 24 '17 at 22:17
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The Earthlike planet is orbiting a primary star with higher mass. Probably, a F6 star as that will "age" faster than our Sun with its temperature rising to levels that the ambient stellar radiation (what we call sunlight here On Earth) will scorch your planet. This will be part of the star's natural development. A F6 star reaches the end of its road in 4.5 billion years. This is the same amount of time for life to evolve on planet Earth and produce the human species. Assume your planet follows exactly the same evolutionary history and its humans will suffer the fate of a scorching planet.

An alternative is that, roughly, one million years ago a small black hole fell into the Sun. Assuming that the black hole doesn't consume the Sun, but accelerating its fusion reactions to a huge extent. It takes on the order of one million years for energy produced at the centre of the Sun to reach the photosphere where it is radiated out into space. The sudden rise in solar radiation will produce a scorched Earth.

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  • $\begingroup$ This is much better answer than the global warming. Global warming will not cause a barren wasteland since all the water will still be on the earth's surface. An unstable or expanding star on the other hand will drive atmosphere and water right out into space, while heating the planet as well. I think blaming some sort of stellar instability might be a more realistic explanation than a black hole. $\endgroup$ – kingledion Oct 3 '16 at 2:14
  • $\begingroup$ @kingledion I agree. A stellar instability would be more realistic. My tired brain couldn't think of a suitable mechanism for one that would fill the bill. I used a small black hole as an all-purpose stand-in for a stellar energy upsurge event. I toyed with ramping up the CNO fusion cycle, but that needed some way of dumping massive amounts of carbon, nitrogen & oxygen into the star's interior. Plus I wasn't sure if it would work. So it was case of bring on the black hole. $\endgroup$ – a4android Oct 3 '16 at 3:51
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The shortest and most plausible answer is wait about 500 million years. The sun, as it undergoes its natural evolution is gradually getting brighter and hotter as the hydrogen fuses in the core and is converted to helium. In about 500 million years the increase in solar energy should have raised the temperature to the point that CO2 extraction by weathering and calcium carbonate formation grossly exceeds natural carbon replacement in the carbon cycle and most plants become extinct. One Billion years in the future, Solar luminosity should have increased to the point that the stratosphere becomes saturated with water, and solar radiation rapidly brakes the water into Hydrogen and Oxygen. The Hydrogen rapidly escapes into space and the Earth dries out in a few million years.

For the purposes of your story, the planet could simply have developed complex life much later in history. On Earth, life was pretty much confined to "pond scum" for 3.5 billion years, with complex life only appearing about 500 million years ago during the "Cambrian Explosion". Why this happened and why at that particular time is hotly debated, so almost any sort of handwave on your part should be acceptable. In other words, your planet is Earth 500 million or more years from now, but the "Cambrian Explosion" is happening today.

Radically changing the eccentricity of a planetary orbit is difficult. The Atomic Rockets "Boom Table" tells us the Earth's rotation energy is 2.1 X 10^21J and the orbital energy of the planet can be calculated here, which if I did it right is also @ 2 X 10^29J. As you can see, it would take a literally astronomical event to pull off. Of course, this would be of such a scale (like a neutron star entering the Solar System) that a lot of other unpleasant events would happen, such as other planets becoming destabilized in their orbits, streams of comets entering the inner solar system due to the gravitational effects of the Neutron star destabilizing cometary orbits in the Oort cloud, the possibility of comet and asteroid strikes on the planet or even massive solar events such as flares and coronal discharges from the Sun itself. I haven't even factored in events like radiation from the Neutron star possibly sterilizing the planet or stripping away the ozone layer, since that is particular to the scenario.

The only other astronomical events with similar power and time scales might be the arrival of a rogue giant planet (Jupiter sized or greater), brown dwarf star or micro black hole, but in all these cases, like the neutron star, the object would have to be moving at incredible velocity through the Solar system to cause the change in a matter of centuries or a single century as you wanted.

More exotic events like the passage of a cosmic string might make the event more localized, although even exotica like that might have unusual or disastrous secondary consequences (the intensity of the gravitational field might induce undesirable tidal events if it passed close to the Earth, for example).

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    $\begingroup$ "Wait 500 million years" is not exactly rapid is it? $\endgroup$ – Giacomo Oct 2 '16 at 6:29
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    $\begingroup$ Patience is a virtue to be cultivated $\endgroup$ – Thucydides Oct 2 '16 at 14:20
  • $\begingroup$ Cosmologically, speaking, a mere blink of the eye. :) $\endgroup$ – a4android Oct 3 '16 at 3:52
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The problem with all of the answers I've seen thus far is that heating up the planet means the climate will be wetter, not drier. Hotter temperatures means faster evaporation, but that water doesn't stay in the atmosphere forever. It all comes down as precipitation. Hotter temperatures makes for more jungles, not more deserts. Ice ages make for larger deserts.

Until, that is, you reach a sufficient temperature to cause a run away greenhouse effect wherein 100% of the surface water evaporates/boils into the atmosphere. This is a run-away effect because water vapor is a greenhouse gas. There is no stable point where the oceans are just like, half the size they are today. Once this process begins, you inevitably end up with another Venus-like world with surface temperatures too hot for any surface water. There will be no oxygen and no humans.

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  • $\begingroup$ Venus has laaaarge amounts of water. Guess why there are no jungles there? $\endgroup$ – Youstay Igo Oct 3 '16 at 5:10
  • $\begingroup$ All the co2 acting as a greenhouse gas, but is it possible we could sequester the carbon in jungles? $\endgroup$ – GoingFTL Oct 22 '17 at 20:35
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Hmm. We have to do something...

  • Orbital Hijinks: I don't like this, because I don't have a nice, gentle way of moving the planet just far enough, that fast.

  • Star Hijinks: I like this. Your star can "heat up" just bit. Hard to justify the rapidity, but you might be able to get away with it.

  • Global Warming Hijinks: Don't like this, because the planet is obviously survivable after burning all fossil fuel. Why? Because that's how hot it was before that planet's Carboniferous period.

Here's a new one...

Let's imagine that the new unpleasant climate is what the climate should have been all along. But the planet had been going through an unnatural cold regime for a million years or so. Why? Because the sun and planet were traveling through a nebula, and the gases and particulates were blocking a certain amount of sunlight away from the planet! Once the trajectory of the solar system takes it away from all that awful space junk, the sunlight starts hitting the planet like a hammer.

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The star has a companion. The companion is a brown dwarf in a very elliptical orbit. It's orbit got slightly jostled when it was out near apoapsis (since the period is so long the actual change can be a few meters per second) and this pushed it's periapsis too low--this time around it's grazing the main star.

Alternately, a comet that is very heavy in CO2 comes flying by. It passes within the Roche limit of the next planet out and is turned into rubble (think of what happened to Shoemaker-Levy 9, just to a much greater degree as the approach was much closer.) This collection of rubble hits the Earth-analogue. Since it's all broken up it burns up in the atmosphere--but dumps a ton of heat and adds a whole bunch of CO2--instant greenhouse.

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