<blockquote>
  <p><em>At what point will the sun make earth uninhabitable for humans?</em></p>
</blockquote>

<p><strong>It nearly happened on May 23, 1967.</strong><br>
According to <a href="http://onlinelibrary.wiley.com/doi/10.1002/2016SW001423/abstract" rel="noreferrer">this history paper</a> released yesterday, summarized nicely <a href="http://www.space.com/33687-solar-storm-cold-war-false-alarm.html" rel="noreferrer">here on Space.com</a>, at the <a href="https://news.agu.org/press-release/1967-solar-storm-nearly-took-us-to-brink-of-war/" rel="noreferrer">American Geophysical Union</a> (paper publisher), and in <a href="https://news.google.com/news/story?ncl=dcciObZkOd2cRTMcLfqXlLVVy2fkM" rel="noreferrer">many other media outlets</a>, a powerful Earth-directed solar flare on that date jammed radar of the US Air Force's Ballistic Missile Early Warning System. Radar jamming like that, especially across all three sites, was considered an act of war, with the Soviet Union as the obvious culprit.  Nuke-laden planes prepared to go destroy the enemy and set off the nuclear war that likely would have rendered Earth uninhabitable for humans.  </p>

<p>Fortunately for all of us, the US had invested resources in monitoring the sun several years earlier, and somebody figured out that this was a solar flare with just enough time to stop the nuclear deliveries and keep the Cold War cold. </p>

<p><a href="http://www.popularmechanics.com/space/a22265/solar-flare-nuclear-war/" rel="noreferrer">Popular Mechanics points out</a>:</p>

<blockquote>
  <p>If that bulletin had been delayed a few minutes, those nuclear aircraft could have launched, and the solar flares would have made it impossible to communicate in the air. If those aircraft had launched, there would have been no way to call them back.</p>
</blockquote>

<hr>

<p><strong>It also nearly happened on September 26, 1983.</strong><br>
With the superpowers again at hair trigger tensions, a rare alignment of <em>sunlight glinting off high altitude clouds</em> and the highly elliptical orbits of Soviet early-warning satellites caused the detection system to report that five intercontinental ballistic missiles, likely carrying nuclear warheads, had been launched by the United States against the Soviet Union.  With only a short time to act on such a report, Soviet leaders likely would have launched a large nuclear strike against the US in retaliation for the detected attack.  However, the human on duty to receive this detection report was civilian-trained Stanislav Petrov, who was skeptical of the detection and correctly classified this as a false alarm.  (Five nuclear missiles seemed small for the kind of attack he expected from the US.)  This <a href="https://en.wikipedia.org/wiki/1983_Soviet_nuclear_false_alarm_incident" rel="noreferrer">decision</a> has been credited with preventing a large-scale nuclear war, which otherwise would have been triggered by misinterpreted sunlight. </p>

<hr>

<p>So a possible answer is, "<strong>the next time some tense socio-technical system we've built misinterprets the Sun.</strong>" </p>

<p><em><a href="https://astronomy.stackexchange.com/questions/17875/when-will-the-sun-end-all-human-life-on-earth/17878?noredirect=1#comment27542_17878">Thanks</a> to user <a href="https://astronomy.stackexchange.com/users/11832/js">JS</a> for the example from September 1983, and to all those who happened to be in the right place at the right time and helped keep us safe.</em></p>

CC BY-SA 3.0
2016-08-10T22:35:10.377Z
This does not answer the question of when the Sun *will* render Earth inhabitable. You simply mention one example of when it *could have*.
Sir Cumference
CC BY-SA 3.0
2016-08-10T22:45:43.403Z
Would "next time people or the automated systems or extremely tense socio-technical systems they build misinterpret solar events as aggression" be a more acceptable answer, Sir?
WBT
CC BY-SA 3.0
2016-08-10T22:51:51.433Z
@SirCumference  Not necessarily.  Maybe it's just an unexpected answer!  (OP is even named "Storm.")  Learning this material, I found it interesting. Others who care about astronomy and/or seek examples of why it's more generally important to care about astronomy might find it interesting too.
WBT
CC BY-SA 3.0
2016-08-11T20:03:16.537Z
@SirCumference No one can say when it *will* render the Earth uninhabitable. Even your answer, which gives 1 billion years as a guess, whilst a good answer, is wild speculation, at best. 1 billion years is a hell of a **long** time in terms of human technological development. I doubt something as trivial as a 47 degrees and water at the poles would be an issue for a human race that has survived and advanced another billion years. We've only been around for about 0.02% of a billion years, and already we can live in extremely harsh conditions such as Antarctica, or the ISS.
JBentley
CC BY-SA 3.0
2016-08-11T20:08:52.783Z
And that's not considering terraforming technologies that could delay such conditions on Earth from occuring in the first place.
JBentley
CC BY-SA 3.0
2016-08-11T20:37:35.627Z
@JBentley "I doubt something as trivial as 47 degrees" tells me that you have a vague understanding of climatology. An average increase of one degree across Earth's entire surface means huge changes in climatic extremes. It's not the same as a single degree on human skin — this is across an entire planet. Between 4 and 5 degrees, rainforests will burn up and turn to desert. At the end of the Permian period (251m years ago), when global temperatures rose by only six degrees, 95% of species were wiped out. 47 degrees will turn the planet into a desolate rock in space.
Sir Cumference
CC BY-SA 3.0
2016-08-11T20:40:42.463Z
@SirCumference *a desolate rock in space* Do you mean like Mars, that desolate rock we're getting ready to colonize with humans, in addition to the robots already there?
WBT
CC BY-SA 3.0
2016-08-11T20:42:18.423Z
@WBT Sigh...no one is getting ready to colonize Mars. We don't nearly have the resources or even proper concepts of how we can do that.
Sir Cumference
CC BY-SA 3.0
2016-08-11T20:51:26.700Z
@SirCumference *no one is getting ready to colonize Mars.*  I don't consider [Elon Musk](http://observer.com/2016/06/elon-musk-charts-path-to-colonizing-mars-within-a-decade/) to be a nobody.  [Mars One](http://www.mars-one.com/) is also getting ready.  There are some seeds pointing to further discussion in the [Wikipedia article about the topic](https://en.wikipedia.org/wiki/Colonization_of_Mars).  We're a ways off (not on a billion-year time scale), but still getting ready.
WBT
CC BY-SA 3.0
2016-08-11T20:55:49.850Z
@WBT You don't understand the effect that increases in temperature have on planets. 7° increase on Earth would make supervolcanoes much more prominent and powerful. They would put nuclear weapons to shame; supervolcanoes like the Yellowstone one can cause continental destruction. Cold temperatures on Mars are incomparable to constant volcanic activity and weather storms.
Sir Cumference
CC BY-SA 3.0
2016-08-11T20:57:57.603Z
@SirCumference Did you mean to direct that last comment at JBentley?  I was just pointing out that some humans are now figuring out how to take what you might describe as "a desolate rock in space" and make it habitable for themselves and their descendants.
WBT
CC BY-SA 3.0
2016-08-11T22:43:04.140Z
@WBT: To yours I'll add [this](https://en.wikipedia.org/wiki/Stanislav_Petrov) and [this](https://en.wikipedia.org/wiki/Vasili_Arkhipov).  Why is it every time someone declines to start a nuclear war, it turns out to have been the right choice?
JS.
CC BY-SA 3.0
2016-08-12T14:40:22.843Z
Those events woudn't have rendered the earth uninhabitable. Cold War becoming hot could cause billions of deaths and could cause a collapse of the world as we know it, but exploding all the nuclear weapons we have, even accounting for the climate aftereffects, would still leave more people alive than there were a few thousand or a few hundred thousand years ago. It wouldn't even render the world totally uninhibited, much less uninhabitable, which is a much stricter criteria.
Peteris
CC BY-SA 4.0
2016-08-10T22:28:31.600Z
2018-07-31T22:12:19.233Z
2018-07-31T22:12:19.233Z
WBT
<p>According to Wikipedia's <a href="https://en.wikipedia.org/wiki/Timeline_of_the_far_future#Future_of_the_Earth.2C_the_Solar_System_and_the_Universe">timeline of the far future</a> this will happen at least in <strong>800 million years</strong> from now:</p>

<blockquote>
  <p>Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible. Free oxygen and ozone disappear from the atmosphere. Multicellular life dies out.</p>
</blockquote>

<p>But it might already end 200 million years earlier:</p>

<blockquote>
  <p>The Sun's increasing luminosity begins to disrupt the carbonate–silicate cycle; higher luminosity increases weathering of surface rocks, which traps carbon dioxide in the ground as carbonate. As water evaporates from the Earth's surface, rocks harden, causing plate tectonics to slow and eventually stop. Without volcanoes to recycle carbon into the Earth's atmosphere, carbon dioxide levels begin to fall. By this time, carbon dioxide levels will fall to the point at which C3 photosynthesis is no longer possible. All plants that utilize C3 photosynthesis (~99 percent of present-day species) will die.</p>
</blockquote>

CC BY-SA 3.0
2016-08-11T11:22:09.237Z
There are already attempts to genetically engineer C4 photosynthesis into crops - 600My should be long enough to crack that.  And it wouldn't be surprising if we could boost the geological sources of CO₂ by then.
Chris H
CC BY-SA 3.0
2016-08-11T11:34:54.670Z
"Free oxygen and ozone disappear from the atmosphere" so if you consider the moon to be uninhabitable...
Sebastian
CC BY-SA 3.0
2016-08-11T11:41:21.770Z
I assumed that the lack of free oxygen was caused by the lack of photosynthesis and would be averted if we could supply CO2
Chris H
CC BY-SA 3.0
2016-08-11T11:47:02.653Z
True, if you imagine such a level of human influence at that time.
Sebastian
CC BY-SA 3.0
2016-08-11T11:54:24.587Z
I took that assumption from the question, though it didn't rule out humanity having regressed to pre-industrial society before that.
Chris H
CC BY-SA 3.0
2016-08-11T12:09:03.140Z
The OP's question was when the Sun would render Earth uninhabitable to humans, not when atmospheric changes would.
Sir Cumference
CC BY-SA 3.0
2016-08-11T13:38:13.463Z
@Sir Cumference: The atmospheric changes are due to the sun's increasing luminocity. I extended the corresponding quote in my answer.
Sebastian
CC BY-SA 3.0
2016-08-13T23:48:50.507Z
Of course, this is the typical kind of prediction that assumes that everything but the monitored quantity stays the same. For example, as carbon dioxide levels drop off slowly, C4 photosynthesising (or whatever better approach appears in the meantime) will be heavily favoured - by the point C3 plants would begin to die off, there would be scarcely any left in the first place. And with plate tectonics stopped, a lot of the carbon wouldn't go back into the mantle to need recycling either - all you need is life that recycles the carbonates, not impossible especially with the increased sun energy.
Luaan
CC BY-SA 3.0
2016-08-11T07:30:08.950Z
2016-08-11T13:36:54.037Z
2016-08-11T13:36:54.037Z
Sebastian
<p>I read a <a href="https://en.wikipedia.org/wiki/Death_from_the_Skies!" rel="nofollow">good book</a> that covered the sun expanding scenario. I don't remember the time line but at some point in its lifetime the sun will grow larger and swallow Mercury and the earth will become too hot to sustain life. </p>

<p>I think this is the scenario you're asking about and others have answered, but in the book he points out that over the vast time scales involved, it's not a very big deal for a space faring civilization to move the Earth out to a safe distance then back in when the sun shrinks.</p>

<p>I would have expected some kind of Star Trek level technology, but he describes how to use a simple <a href="https://en.wikipedia.org/wiki/Gravity_tractor" rel="nofollow">Gravity tractor</a> (not to be confused with a Tractor Beam) to adjust comets flight paths to speed up the earth (the reverse of the gravity slingshot used to speed up our current space probes) moving it further away from the sun.</p>

<p>So to answer your original question assuming the human life on earth is still advanced and spacefaring, human life on earth could last until the sun burns out and maybe a bit beyond that.</p>

CC BY-SA 3.0
2016-08-12T10:43:43.287Z
The sun will go red giant and swallow Mercury and probably Venus in about 5 billion years, but it will make the Earth too hot for most life long before then.    The increased luminosity of the sun could make life unsustainable for us humans in as little as 600 million years.    A gravity tractor would require a lot of work and energy, but with 600 million years to accomplish it, it's certainly possible.  Gravity assists are also possible.
userLTK
CC BY-SA 4.0
2018-07-30T23:23:26.853Z
The answer above is reminder not to count out human resourcefulness (if we don't kill ourselves first). I think we will be able to and should move the Earth farther from the Sun over a 600 million year period (or so). There will never be a better place for Earth-life (including humans) than the place we co-evolved with for 4 billion years. I think the question assumes that we don't move the Earth.
Jack R. Woods
CC BY-SA 3.0
2016-08-11T10:48:40.443Z
2016-08-12T20:30:15.410Z
2016-08-12T20:30:15.410Z
Mikey Mouse
<p>I would be very surprised if the sun ever ends all life on Earth.</p>

<p>1)  If we care about the Earth we will move it.  If we are still around by then it certainly will be within our technology.</p>

<p>2)  I would say the most likely outcome (assuming we survive) is that the Earth gets taken apart for building materials.  It's an awful lot of mass simply being used as a gravity source--incredibly inefficient.</p>

CC BY-SA 3.0
2016-08-14T11:22:03.490Z
I think an orbital mirror in L1 would solve the problem much easier.
peterh
CC BY-SA 3.0
2016-08-12T18:51:54.540Z
2016-08-12T18:51:54.540Z
Loren Pechtel
<p>The Sun is gradually getting larger and brighter. In fact, as called2voyage pointed out, its brightness is increasing by 1% every 100 million years. You can see how the Sun will change in the future from this graph: (<a href="https://en.wikipedia.org/wiki/Sun#Main_sequence" rel="noreferrer">Source</a>)</p>

<p><a href="https://i.sstatic.net/loYwr.png" rel="noreferrer"><img src="https://i.sstatic.net/loYwr.png" alt="enter image description here"></a></p>

<p>According to <a href="http://adsabs.harvard.edu/abs/2009PNAS..106.9576L" rel="noreferrer">this paper</a>, within 1 billion (short scale) years from now, the ever-increasing luminosity will have made Earth nearly uninhabitable. The average temperature will have reached 47°C, compared to its current 15°C. Essentially no water will be left either, except at the poles. This may allow for simple life to survive for a while.</p>

<p>By 3.5 billion years, Earth will no longer resemble its current self. Its oceans, magnetic field and ozone layer and plate tectonics will be no more. Its surface temperature will skyrocket to roughly 1,330°C, hot enough to melt surface rock. No longer will our planet resemble a pale blue dot, and it will be more like Venus. Our planet is officially dead, along with all life on it. (<a href="https://www.newscientist.com/article/mg14219191.900-science-fiery-future-for-planet-earth-/" rel="noreferrer">Source</a>)</p>

<p>~4.5 billion years from now, the Sun will become a red giant and possibly consume Earth. However, according to <a href="http://adsabs.harvard.edu/abs/2003AsBio...3..317S" rel="noreferrer">this paper</a>, it may heat up potentially habitable bodies like Triton, to the point where they would support life. Unfortunately, the Sun won't remain in this stage for long enough — life usually takes billions of years to develop.</p>

CC BY-SA 3.0
2016-08-11T09:11:29.593Z
Great answer, although I'm not sure we can truthfully assert _"life usually takes billions of years to develop"_ when we've only "witnessed" it once.
Lightness Races in Orbit
CC BY-SA 3.0
2016-08-11T13:31:10.080Z
@LightnessRacesinOrbit I agree. It is also unclear what form of life is being referred to.
called2voyage
CC BY-SA 3.0
2016-08-11T16:03:17.390Z
@LightnessRacesinOrbit Considering it took billions of years for life to develop on Earth, we can safely rule out life appearing in the time the Sun is post-main sequence.
Sir Cumference
CC BY-SA 3.0
2016-08-11T17:16:28.500Z
@SirCumference: How so?
Lightness Races in Orbit
CC BY-SA 3.0
2016-08-11T17:32:53.933Z
@SirCumference based on a very representative sample of 1?
njzk2
CC BY-SA 3.0
2016-08-11T21:21:28.433Z
It also depends on what definition of "develop" you use, as the earliest evidence for life we have here shows that life was present within 400 million years after earth's formation.
whatsisname
CC BY-SA 3.0
2016-08-11T21:22:11.763Z
Related to "life usually takes billions of years to develop". (1) development is the process by which one individual goes through the different stages of life (typically from a single cell to a grown up for multicellular lineages). The correct term is probably "originates" or "evolve" (but I am not sure what you meant exactly), no "develop" (2) Life took about 0.5 billions years to first appear on earth and much less time when you consider the existence of a range of 'putatively appropriate' conditions for life to originate. (3) Generalization from a single observation is likely misleading.
Remi.b
CC BY-SA 3.0
2016-08-11T21:31:11.017Z
Off-topic: What caused that big dip in luminosity half a billion years after the sun started to shine?
Shane
CC BY-SA 3.0
2016-08-11T22:06:21.063Z
@Shane I assume it's because that was when the Sun finished its contraction and became main-sequence. Before that point, the Sun was constantly losing energy as it shined. After it became main-sequence, nuclear fusion started producing much more energy.
Sir Cumference
CC BY-SA 3.0
2016-08-11T22:07:25.157Z
Ahh. I thought the zero point was when it became main sequence.
Shane
CC BY-SA 3.0
2016-08-11T22:36:10.577Z
Alright everyone.  You heard the man.  We've got 1 billion years before this thing is uninhabitable.  Let's get moving, people!
JS.
CC BY-SA 3.0
2016-08-12T10:36:53.367Z
While I'm nowhere close to an expert in simple life's biological development, I think Sir Cumference has a point, that even if it's a sample size of one, there's many steps between simple, first forms of life, and your basic, DNA based, photosynthetic with a nucleus.   There's many more steps before you get multi celled, and after that, there's another long time before things like eyes and teeth, and a brain develop within that multi-cellular organism.   It doesn't happen quickly, but once life get eyes, teeth, a brain and competition, then it things can progress fairly fast. (IMHO).
userLTK
CC BY-SA 3.0
2016-08-13T23:36:27.080Z
@userLTK It's really hard to tell with the tiny sample size. For example, a lot of the "leaps" in complexity happened during (or after) a catastrophe of some kind. It might very well be that life on another planet might have been luckier and got their catastrophes earlier (if there is any causal connection in the first place, of course). We don't know how many kinds of life have existed in the past - we only have a very spotty record and a lot of indirect evidence. Heck, it's possible (though unlikely) that there was intelligent life on Earth before us and we just didn't find any record yet.
Luaan
CC BY-SA 3.0
2016-08-13T23:40:40.957Z
@userLTK And we have plenty of evidence that when the evolutionary pressure is high, the "development" can get very fast indeed - while when food is abundant and there's not a lot of competition, it can stagnate for hundreds of millions of years. You also get stagnation when things get *too* harsh. There's so many unknowns and variables that we just can't tell - it's not like there's a physical law that prevents an advanced form of life from developing within a hundred million years; we just don't have any evidence that it did on Earth in the past.
Luaan
CC BY-SA 3.0
2016-08-14T22:02:43.400Z
@Luaan I'm not an expert in such things, and I'm not sure anyone is, since we didn't see it happen and there's only fossil records, but there's an enormous variation in one celled life and many steps that need to take place just to get the first bug, or, the first plant.   I remain skeptical that it can happen "quickly".   There may be no physical law, but there may be a practical limit of at least a few hundred million years for first-early life to become complex, animals, fish and plants  (IMHO).   I do agree with you that there are significant unknowns.
userLTK
CC BY-SA 3.0
2016-08-10T19:59:26.727Z
2016-08-10T21:05:24.140Z
2016-08-10T21:05:24.140Z
Sir Cumference
<p>If nothing else wipes out human existence prior to this, at what point will the Sun make Earth uninhabitable for humans?</p>

CC BY-SA 3.0
2016-08-11T18:33:31.087Z
You're already assuming we don't destroy the Sun in the interim. It's a damn good source of raw materials.
Patrick Stevens
CC BY-SA 3.0
2016-08-11T19:28:04.947Z
@PatrickStevens Not all that good. It is mainly hydrogen and that isn't exactly rare. All those materials are very hot and at the bottom of a deep, deep gravity well. At the very least, we aren't going to be horning in on the sun until Jupiter is gone.
Shane
CC BY-SA 3.0
2016-08-11T19:31:46.013Z
You're already assuming the Sun will get a chance to before... we do.
corsiKa
CC BY-SA 3.0
2016-08-11T20:11:57.250Z
@corsiKa He covered that with, *"If nothing else wipes out human existence prior to this"*.
JBentley
CC BY-SA 3.0
2016-08-11T20:47:28.337Z
@Shane And we have of the order of a billion years to play with! Pretty sure we'll exhaust Jupiter in that time.
Patrick Stevens
CC BY-SA 3.0
2016-08-12T16:59:10.140Z
Relevant: [Distant future of the Sun and Earth revisited](http://arxiv.org/abs/0801.4031) and [this answer](http://astronomy.stackexchange.com/questions/1911/what-will-happen-to-life-on-earth-when-the-andromeda-and-milky-way-galaxies-coll/1916#1916) to the question [What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?](http://astronomy.stackexchange.com/questions/1911) Notably: We only have 1, maybe 2, billion years before water boils off the surface, at which point I think we can make the claim that Earth no longer sustains life.
Adam Davis
CC BY-SA 3.0
2016-08-12T17:10:44.497Z
Are you assuming that "humans" will be the same then, in thousands of millions of years, as we are now, which we have only been for a few hundred thousand years?
user
CC BY-SA 3.0
2016-08-13T21:53:00.730Z
I have seen claims of 200 million as well as 5000 million years but neither claim was providing any sources, so you have my thumbs up for this question.
kasperd
<the-sun>
When will the Sun end all human life on Earth?
Daniel Storm
# When will the Sun end all human life on Earth?

(Asked by: username_0 on 2016-08-10)

If nothing else wipes out human existence prior to this, at what point will the Sun make Earth uninhabitable for humans?

**Tags:** the-sun
> **Comments:**
> **username_1**: You're already assuming we don't destroy the Sun in the interim. It's a damn good source of raw materials.  
> **username_2**: @PatrickStevens Not all that good. It is mainly hydrogen and that isn't exactly rare. All those materials are very hot and at the bottom of a deep, deep gravity well. At the very least, we aren't going to be horning in on the sun until Jupiter is gone.  
> **username_3**: You're already assuming the Sun will get a chance to before... we do.  
> **username_4**: @corsiKa He covered that with, *"If nothing else wipes out human existence prior to this"*.  
> **username_1**: @Shane And we have of the order of a billion years to play with! Pretty sure we'll exhaust Jupiter in that time.  
> **username_5**: Relevant: [Distant future of the Sun and Earth revisited](http://arxiv.org/abs/0801.4031) and [this answer](http://astronomy.stackexchange.com/questions/1911/what-will-happen-to-life-on-earth-when-the-andromeda-and-milky-way-galaxies-coll/1916#1916) to the question [What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?](http://astronomy.stackexchange.com/questions/1911) Notably: We only have 1, maybe 2, billion years before water boils off the surface, at which point I think we can make the claim that Earth no longer sustains life.  
> **username_6**: Are you assuming that "humans" will be the same then, in thousands of millions of years, as we are now, which we have only been for a few hundred thousand years?  
> **username_7**: I have seen claims of 200 million as well as 5000 million years but neither claim was providing any sources, so you have my thumbs up for this question.  

---

## 5 answers

### Answer by username_9 on 2016-08-10. Score: 68 | Accepted answer

The Sun is gradually getting larger and brighter. In fact, as called2voyage pointed out, its brightness is increasing by 1% every 100 million years. You can see how the Sun will change in the future from this graph: ([Source](https://en.wikipedia.org/wiki/Sun#Main_sequence))

[![enter image description here](https://i.sstatic.net/loYwr.png)](https://i.sstatic.net/loYwr.png)

According to [this paper](http://adsabs.harvard.edu/abs/2009PNAS..106.9576L), within 1 billion (short scale) years from now, the ever-increasing luminosity will have made Earth nearly uninhabitable. The average temperature will have reached 47°C, compared to its current 15°C. Essentially no water will be left either, except at the poles. This may allow for simple life to survive for a while.

By 3.5 billion years, Earth will no longer resemble its current self. Its oceans, magnetic field and ozone layer and plate tectonics will be no more. Its surface temperature will skyrocket to roughly 1,330°C, hot enough to melt surface rock. No longer will our planet resemble a pale blue dot, and it will be more like Venus. Our planet is officially dead, along with all life on it. ([Source](https://www.newscientist.com/article/mg14219191.900-science-fiery-future-for-planet-earth-/))

~4.5 billion years from now, the Sun will become a red giant and possibly consume Earth. However, according to [this paper](http://adsabs.harvard.edu/abs/2003AsBio...3..317S), it may heat up potentially habitable bodies like Triton, to the point where they would support life. Unfortunately, the Sun won't remain in this stage for long enough — life usually takes billions of years to develop.

> **Comments:**
> **username_20**: Great answer, although I'm not sure we can truthfully assert _"life usually takes billions of years to develop"_ when we've only "witnessed" it once.  
> **username_21**: @LightnessRacesinOrbit I agree. It is also unclear what form of life is being referred to.  
> **username_9**: @LightnessRacesinOrbit Considering it took billions of years for life to develop on Earth, we can safely rule out life appearing in the time the Sun is post-main sequence.  
> **username_20**: @SirCumference: How so?  
> **username_22**: @SirCumference based on a very representative sample of 1?  
> **username_23**: It also depends on what definition of "develop" you use, as the earliest evidence for life we have here shows that life was present within 400 million years after earth's formation.  
> **username_24**: Related to "life usually takes billions of years to develop". (1) development is the process by which one individual goes through the different stages of life (typically from a single cell to a grown up for multicellular lineages). The correct term is probably "originates" or "evolve" (but I am not sure what you meant exactly), no "develop" (2) Life took about 0.5 billions years to first appear on earth and much less time when you consider the existence of a range of 'putatively appropriate' conditions for life to originate. (3) Generalization from a single observation is likely misleading.  
> **username_2**: Off-topic: What caused that big dip in luminosity half a billion years after the sun started to shine?  
> **username_9**: @Shane I assume it's because that was when the Sun finished its contraction and became main-sequence. Before that point, the Sun was constantly losing energy as it shined. After it became main-sequence, nuclear fusion started producing much more energy.  
> **username_2**: Ahh. I thought the zero point was when it became main sequence.  
> **username_10**: Alright everyone.  You heard the man.  We've got 1 billion years before this thing is uninhabitable.  Let's get moving, people!  
> **username_16**: While I'm nowhere close to an expert in simple life's biological development, I think Sir Cumference has a point, that even if it's a sample size of one, there's many steps between simple, first forms of life, and your basic, DNA based, photosynthetic with a nucleus.   There's many more steps before you get multi celled, and after that, there's another long time before things like eyes and teeth, and a brain develop within that multi-cellular organism.   It doesn't happen quickly, but once life get eyes, teeth, a brain and competition, then it things can progress fairly fast. (IMHO).  
> **username_14**: @userLTK It's really hard to tell with the tiny sample size. For example, a lot of the "leaps" in complexity happened during (or after) a catastrophe of some kind. It might very well be that life on another planet might have been luckier and got their catastrophes earlier (if there is any causal connection in the first place, of course). We don't know how many kinds of life have existed in the past - we only have a very spotty record and a lot of indirect evidence. Heck, it's possible (though unlikely) that there was intelligent life on Earth before us and we just didn't find any record yet.  
> **username_14**: @userLTK And we have plenty of evidence that when the evolutionary pressure is high, the "development" can get very fast indeed - while when food is abundant and there's not a lot of competition, it can stagnate for hundreds of millions of years. You also get stagnation when things get *too* harsh. There's so many unknowns and variables that we just can't tell - it's not like there's a physical law that prevents an advanced form of life from developing within a hundred million years; we just don't have any evidence that it did on Earth in the past.  
> **username_16**: @Luaan I'm not an expert in such things, and I'm not sure anyone is, since we didn't see it happen and there's only fossil records, but there's an enormous variation in one celled life and many steps that need to take place just to get the first bug, or, the first plant.   I remain skeptical that it can happen "quickly".   There may be no physical law, but there may be a practical limit of at least a few hundred million years for first-early life to become complex, animals, fish and plants  (IMHO).   I do agree with you that there are significant unknowns.  

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### Answer by username_8 on 2016-08-10. Score: 48

> *At what point will the sun make earth uninhabitable for humans?*

**It nearly happened on May 23, 1967.**  
According to [this history paper](http://onlinelibrary.wiley.com/doi/10.1002/2016SW001423/abstract) released yesterday, summarized nicely [here on Space.com](http://www.space.com/33687-solar-storm-cold-war-false-alarm.html), at the [American Geophysical Union](https://news.agu.org/press-release/1967-solar-storm-nearly-took-us-to-brink-of-war/) (paper publisher), and in [many other media outlets](https://news.google.com/news/story?ncl=dcciObZkOd2cRTMcLfqXlLVVy2fkM), a powerful Earth-directed solar flare on that date jammed radar of the US Air Force's Ballistic Missile Early Warning System. Radar jamming like that, especially across all three sites, was considered an act of war, with the Soviet Union as the obvious culprit. Nuke-laden planes prepared to go destroy the enemy and set off the nuclear war that likely would have rendered Earth uninhabitable for humans.

Fortunately for all of us, the US had invested resources in monitoring the sun several years earlier, and somebody figured out that this was a solar flare with just enough time to stop the nuclear deliveries and keep the Cold War cold.

[Popular Mechanics points out](http://www.popularmechanics.com/space/a22265/solar-flare-nuclear-war/):

> If that bulletin had been delayed a few minutes, those nuclear aircraft could have launched, and the solar flares would have made it impossible to communicate in the air. If those aircraft had launched, there would have been no way to call them back.

---

**It also nearly happened on September 26, 1983.**  
With the superpowers again at hair trigger tensions, a rare alignment of *sunlight glinting off high altitude clouds* and the highly elliptical orbits of Soviet early-warning satellites caused the detection system to report that five intercontinental ballistic missiles, likely carrying nuclear warheads, had been launched by the United States against the Soviet Union. With only a short time to act on such a report, Soviet leaders likely would have launched a large nuclear strike against the US in retaliation for the detected attack. However, the human on duty to receive this detection report was civilian-trained Stanislav Petrov, who was skeptical of the detection and correctly classified this as a false alarm. (Five nuclear missiles seemed small for the kind of attack he expected from the US.) This [decision](https://en.wikipedia.org/wiki/1983_Soviet_nuclear_false_alarm_incident) has been credited with preventing a large-scale nuclear war, which otherwise would have been triggered by misinterpreted sunlight.

---

So a possible answer is, "**the next time some tense socio-technical system we've built misinterprets the Sun.**"

*[Thanks](https://astronomy.stackexchange.com/questions/17875/when-will-the-sun-end-all-human-life-on-earth/17878?noredirect=1#comment27542_17878) to user [JS](https://astronomy.stackexchange.com/users/11832/js) for the example from September 1983, and to all those who happened to be in the right place at the right time and helped keep us safe.*

> **Comments:**
> **username_9**: This does not answer the question of when the Sun *will* render Earth inhabitable. You simply mention one example of when it *could have*.  
> **username_8**: Would "next time people or the automated systems or extremely tense socio-technical systems they build misinterpret solar events as aggression" be a more acceptable answer, Sir?  
> **username_8**: @SirCumference  Not necessarily.  Maybe it's just an unexpected answer!  (OP is even named "Storm.")  Learning this material, I found it interesting. Others who care about astronomy and/or seek examples of why it's more generally important to care about astronomy might find it interesting too.  
> **username_4**: @SirCumference No one can say when it *will* render the Earth uninhabitable. Even your answer, which gives 1 billion years as a guess, whilst a good answer, is wild speculation, at best. 1 billion years is a hell of a **long** time in terms of human technological development. I doubt something as trivial as a 47 degrees and water at the poles would be an issue for a human race that has survived and advanced another billion years. We've only been around for about 0.02% of a billion years, and already we can live in extremely harsh conditions such as Antarctica, or the ISS.  
> **username_4**: And that's not considering terraforming technologies that could delay such conditions on Earth from occuring in the first place.  
> **username_9**: @JBentley "I doubt something as trivial as 47 degrees" tells me that you have a vague understanding of climatology. An average increase of one degree across Earth's entire surface means huge changes in climatic extremes. It's not the same as a single degree on human skin — this is across an entire planet. Between 4 and 5 degrees, rainforests will burn up and turn to desert. At the end of the Permian period (251m years ago), when global temperatures rose by only six degrees, 95% of species were wiped out. 47 degrees will turn the planet into a desolate rock in space.  
> **username_8**: @SirCumference *a desolate rock in space* Do you mean like Mars, that desolate rock we're getting ready to colonize with humans, in addition to the robots already there?  
> **username_9**: @WBT Sigh...no one is getting ready to colonize Mars. We don't nearly have the resources or even proper concepts of how we can do that.  
> **username_8**: @SirCumference *no one is getting ready to colonize Mars.*  I don't consider [Elon Musk](http://observer.com/2016/06/elon-musk-charts-path-to-colonizing-mars-within-a-decade/) to be a nobody.  [Mars One](http://www.mars-one.com/) is also getting ready.  There are some seeds pointing to further discussion in the [Wikipedia article about the topic](https://en.wikipedia.org/wiki/Colonization_of_Mars).  We're a ways off (not on a billion-year time scale), but still getting ready.  
> **username_9**: @WBT You don't understand the effect that increases in temperature have on planets. 7° increase on Earth would make supervolcanoes much more prominent and powerful. They would put nuclear weapons to shame; supervolcanoes like the Yellowstone one can cause continental destruction. Cold temperatures on Mars are incomparable to constant volcanic activity and weather storms.  
> **username_8**: @SirCumference Did you mean to direct that last comment at JBentley?  I was just pointing out that some humans are now figuring out how to take what you might describe as "a desolate rock in space" and make it habitable for themselves and their descendants.  
> **username_10**: @WBT: To yours I'll add [this](https://en.wikipedia.org/wiki/Stanislav_Petrov) and [this](https://en.wikipedia.org/wiki/Vasili_Arkhipov).  Why is it every time someone declines to start a nuclear war, it turns out to have been the right choice?  
> **username_11**: Those events woudn't have rendered the earth uninhabitable. Cold War becoming hot could cause billions of deaths and could cause a collapse of the world as we know it, but exploding all the nuclear weapons we have, even accounting for the climate aftereffects, would still leave more people alive than there were a few thousand or a few hundred thousand years ago. It wouldn't even render the world totally uninhibited, much less uninhabitable, which is a much stricter criteria.  

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### Answer by username_12 on 2016-08-11. Score: 13

According to Wikipedia's [timeline of the far future](https://en.wikipedia.org/wiki/Timeline_of_the_far_future#Future_of_the_Earth.2C_the_Solar_System_and_the_Universe) this will happen at least in **800 million years** from now:

> Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible. Free oxygen and ozone disappear from the atmosphere. Multicellular life dies out.

But it might already end 200 million years earlier:

> The Sun's increasing luminosity begins to disrupt the carbonate–silicate cycle; higher luminosity increases weathering of surface rocks, which traps carbon dioxide in the ground as carbonate. As water evaporates from the Earth's surface, rocks harden, causing plate tectonics to slow and eventually stop. Without volcanoes to recycle carbon into the Earth's atmosphere, carbon dioxide levels begin to fall. By this time, carbon dioxide levels will fall to the point at which C3 photosynthesis is no longer possible. All plants that utilize C3 photosynthesis (~99 percent of present-day species) will die.

> **Comments:**
> **username_13**: There are already attempts to genetically engineer C4 photosynthesis into crops - 600My should be long enough to crack that.  And it wouldn't be surprising if we could boost the geological sources of CO₂ by then.  
> **username_12**: "Free oxygen and ozone disappear from the atmosphere" so if you consider the moon to be uninhabitable...  
> **username_13**: I assumed that the lack of free oxygen was caused by the lack of photosynthesis and would be averted if we could supply CO2  
> **username_12**: True, if you imagine such a level of human influence at that time.  
> **username_13**: I took that assumption from the question, though it didn't rule out humanity having regressed to pre-industrial society before that.  
> **username_9**: The OP's question was when the Sun would render Earth uninhabitable to humans, not when atmospheric changes would.  
> **username_12**: @Sir Cumference: The atmospheric changes are due to the sun's increasing luminocity. I extended the corresponding quote in my answer.  
> **username_14**: Of course, this is the typical kind of prediction that assumes that everything but the monitored quantity stays the same. For example, as carbon dioxide levels drop off slowly, C4 photosynthesising (or whatever better approach appears in the meantime) will be heavily favoured - by the point C3 plants would begin to die off, there would be scarcely any left in the first place. And with plate tectonics stopped, a lot of the carbon wouldn't go back into the mantle to need recycling either - all you need is life that recycles the carbonates, not impossible especially with the increased sun energy.  

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### Answer by username_15 on 2016-08-11. Score: 4

I read a [good book](https://en.wikipedia.org/wiki/Death_from_the_Skies!) that covered the sun expanding scenario. I don't remember the time line but at some point in its lifetime the sun will grow larger and swallow Mercury and the earth will become too hot to sustain life.

I think this is the scenario you're asking about and others have answered, but in the book he points out that over the vast time scales involved, it's not a very big deal for a space faring civilization to move the Earth out to a safe distance then back in when the sun shrinks.

I would have expected some kind of Star Trek level technology, but he describes how to use a simple [Gravity tractor](https://en.wikipedia.org/wiki/Gravity_tractor) (not to be confused with a Tractor Beam) to adjust comets flight paths to speed up the earth (the reverse of the gravity slingshot used to speed up our current space probes) moving it further away from the sun.

So to answer your original question assuming the human life on earth is still advanced and spacefaring, human life on earth could last until the sun burns out and maybe a bit beyond that.

> **Comments:**
> **username_16**: The sun will go red giant and swallow Mercury and probably Venus in about 5 billion years, but it will make the Earth too hot for most life long before then.    The increased luminosity of the sun could make life unsustainable for us humans in as little as 600 million years.    A gravity tractor would require a lot of work and energy, but with 600 million years to accomplish it, it's certainly possible.  Gravity assists are also possible.  
> **username_17**: The answer above is reminder not to count out human resourcefulness (if we don't kill ourselves first). I think we will be able to and should move the Earth farther from the Sun over a 600 million year period (or so). There will never be a better place for Earth-life (including humans) than the place we co-evolved with for 4 billion years. I think the question assumes that we don't move the Earth.  

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### Answer by username_18 on 2016-08-12. Score: 3

I would be very surprised if the sun ever ends all life on Earth.

1) If we care about the Earth we will move it. If we are still around by then it certainly will be within our technology.

2) I would say the most likely outcome (assuming we survive) is that the Earth gets taken apart for building materials. It's an awful lot of mass simply being used as a gravity source--incredibly inefficient.

> **Comments:**
> **username_19**: I think an orbital mirror in L1 would solve the problem much easier.  

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