Assuming we have a world at the same stage in global warming as the Earth, with all other properties similar (population, carbon emissions, general climate, orbit, etc.) How long will it be until the Earth reaches a 'no going back' point?

That might be worded badly, so let me give you an example.

I want the Earth to look like Venus with similar properties in the future (it is a common theme on Worldbuilding) with a runaway greenhouse effect. Assuming carbon emissions continue on their present trend, at what point would we reach the Tipping Point?

  • $\begingroup$ You mean the Tipping point? $\endgroup$ – ratchet freak Apr 28 '15 at 15:30
  • $\begingroup$ @ratchetfreak That's the word I was looking for! Thanks......I guess I had a brain fart :) $\endgroup$ – the_OTHER_DJMethaneMan Apr 28 '15 at 15:32
  • $\begingroup$ Close voter, how is this not about Worldbuilding? $\endgroup$ – the_OTHER_DJMethaneMan Apr 28 '15 at 15:34
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    $\begingroup$ Can you explain how this is about world building? It looks to me like a subject for scientific research. $\endgroup$ – Frostfyre Apr 28 '15 at 16:01
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    $\begingroup$ We already have reached the tipping point; positive feedback loops ensure that no matter what we do now, global warming will not stop. $\endgroup$ – theonlygusti Apr 28 '15 at 16:08

Tipping point logic is a flawed line of thought...human thinking enjoys the single line on a graph that when something goes beyond this point all is changed forever and no going back ever! That really isn't true...it's such a dynamic system that there can never be one a point 'tipping point' despite how much we want to think it. So the easy answer to the question 'when do we reach the tipping point' is "there is no tipping point and it's fallacy of human thinking". The globe has warmed and cooled, iced over to a near snowball to so warm that greenland supported tropical marshes...it's recovered from massive volcanic and asteroid upheaval and nuclear winters that stem from them. None of those events tipped the earth into a Venus like state...a little CO2 from us isn't going to change that (especially if you consider how CO2 heavy our globe once was compared to today).

Two key things that will prevent the Earth from looking like Venus. The ocean is the first and foremost...if this thread is entirely around CO2 emissions forcing the earth to venus like conditions, the oceans will heavily prevent that by asorbing a silly amount of CO2. The ocean manages to sequester a huge amount of our CO2 emissions in processes we don't quite understand. The ocean will likely go acidic if it's pushed too far, but it does limit what effects CO2 has on our globe. The shifting of states of water between solid,liquid,and gas also require such a large amount of energy that it provides quite the temperature buffer as well.

The second is plate tectonics. Venus is a single shell around it's mantle and when energy needs to get out, it gets out in the form of giant volcanoes releasing a huge amount of sulphur and co2 into it's atmosphere. This is very different than earth where the majority of this energy is consumed by the moving plates instead of injecting it into our atmosphere.

Just to clarify, this isn't a GW denial style post. Just pointing out in the past far more serious events didn't turn Earth into what Venus is today and our environment is far more resilient and ever changing than we think. There is no tipping point that we can reach with CO2 that would ever result in a Venus like environment.

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    $\begingroup$ This "no tipping point" is nice when you have the luxury of looking at it from a multi-million year perspective, but perhaps not so useful if you re-word the question to something like "At what point does the system quickly accelerate to a Permian/Triassic-like 'Great Dying', thus rendering most higher life forms - including humans - extinct?" $\endgroup$ – jamesqf Apr 28 '15 at 18:46
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    $\begingroup$ @jamesqf The question was about producing a runaway that leads to Venus-like conditions. Twelfth is right, that's not going to happen. While we could get a Great Dying we are adaptable enough that I think at least some of us would survive. $\endgroup$ – Loren Pechtel Apr 28 '15 at 23:45
  • $\begingroup$ @Loren Pechtel: I very seriously doubt that. The idea that humans are spectacularly adaptable is a myth. They've been good at figuring out ways to use the ecosystems they live in, often destroying them in the process, after which they move elsewhere. This is not a real good survival strategy when you run out of elsewheres to move too. See for instance Easter Island. $\endgroup$ – jamesqf Apr 29 '15 at 18:19
  • $\begingroup$ @jamesqf Warming can be countered by moving to colder climates--we can cross inhospitable terrain far better than plants and animals can. So long as any place is cool enough we could survive the warming. (Whether we would survive fighting over the habitable areas is another matter...) $\endgroup$ – Loren Pechtel Apr 30 '15 at 1:37
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    $\begingroup$ @jamesqf It would be pretty nasty but that's not the same thing as completely unsurvivable. We have the technology to survive the Permian-Triassic extinction, albeit probably only a fairly small population. $\endgroup$ – Loren Pechtel May 2 '15 at 1:31

I don't think Earth could become like Venus, with such a thick atmosphere and no water. Earth has an active carbon cycle with excess CO2 reacting with rocks and forming limestone or something like that. Active plate technonics is a game changer: things turn over and can continue to drive feedback mechanisms.

Earth has been through mass extinctions before, and CO2 produced by vulcanism can cause cataclysmic overheating (Permian great dying) and also bring it out of a Snowball Earth state.

To cause such a change nas you ask, the push would have to be harder than anything that's been seen to date by orders of magnitude, or the Earth's dynamics need to be killed.

One can wonder why Venus does not have plate techtonics like Earth: the wide scale melting rather than venting heat points to thicker crust or different composition — nothing that will change here to such a degree. You might ask how the oceans could disappear.

Keep in mind that it's not the Earth that's in trouble; it's just our habitat, a thin vineer of living matter and a current set of comfortable conditions. No matter how bad the mass extinction, life recovers in 10 to 20 million years. No matter how far from comfortable the climate gets, it changes again and recovers the long-term behavior.



Both $CO_2$ concentrations and temperature have been much higher than current levels. In fact, the average $CO_2$ concentrations and temperature for the Earth were higher than they are today.

Earth's Temperature and $CO_2$ history:
Earth's Temperature and $CO_2$ history

None of those lead to a "run-away" or "point of no return" climate events - let alone turning the planet into one like Venus. Most likely, now is no different from then.

Feedback loops

From a controls perspective, the fact that the Earth's climate has remained relatively stable over billions of years is very strong evidence that the climate system over all is a negative feedback loop (meaning it is stable).

The alternative (and this is another strong possibility) is that the Earth's climate is really metastable. Meaning, the Earth's climate will tend to return to its current baseline even if you introduce events to push it away from its normal climate.

However, if you push hard enough on one climate parameter (e.g. introducing more $CO_2$) the Earth's climate will eventually go through a transition to a new metastable state (probably a higher temperature).

Earth Climate is likely Metastable:
Earth's Climate is Metastable

Current state of the art climate models disagree with measurements and each other on what might cause the transition to a new state AND what temperature that new state might be the new average.

Hothouse Earth

Although human activity could cause an undesired warming of the Earth is certainly possible (even likely), there's no way for human activity to cause the Earth to become Venus like in the current era. However, within 1.6-2.5 billion years, the gradually brightening Sun will warm the Earth enough to evaporate ocean water leading to a run-away greenhouse. The Earth will reach this tipping point regardless of what humanity does.

Something even scarier

In the Earth's ancient past (2+ billion years ago), the Earth's surface chemistry transitioned from a reducing atmosphere (e.g. Methane dominant) to an oxidizing atmosphere (e.g. Oxygen dominant). This killed most life on the planet.

Free oxygen is toxic to obligate anaerobic organisms, and the rising concentrations may have wiped out most of the Earth's anaerobic inhabitants at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earth's history.

Changing the fundamental chemistry of the planet's surface would be far scarier and more dangerous to the human race than an increase in a couple of degrees of temperature.

Fortunately, we see no evidence of this happening during the current era.

The Oxygen environment biology has access to much more energy than the organisms evolved for the reducing atmosphere. The dominance of Aerobic organisms creates a strong feedback loops among life forms help stabilize the system and ensure that as long as Earth teams with life that life will work to ensure we don't seen another event like the Oxygen Catastrophe.


Let's concede that global warming is pretty much exactly anthropogenic and disastrous in scale. Now, assume it is 2100 and temps. match the worst of the current models or worse. So it's hot and getting hotter.

There is still no tipping point because man will actively attempt to change the environment. We cut back our CO2, methane, etc. that contribute to warming, not enough to the barest possible minimum, e.g. humans still emit CO2. So we start actively sucking CO2 out of the environment -- not impossible to do if you are willing to expend the effort. Maybe a combination of increase vegetation capture and more technological means.

Still not enough? Change the albedo of the earth, reducing the amount of solar energy retained in the first place.

The measures would be incredibly expensive (and others even more expensive are possible) -- But if the alternative were death for everybody, we would spend the resources.

  • $\begingroup$ Ask yourself why GW predictions generally only go out to 2100. If you assume 2500, then the likelihood of humans not being around to care increases considerably. As for humans doing anything significant to fix the problems... Well, not on current evidence, they won't. A small minority of intelligent & sensible people may try, but their efforts will be rendered null & void by denialists, consumerists, religious/ethnic believers who think they need to outbreed other religions/ethnicities... $\endgroup$ – jamesqf May 2 '15 at 1:27

There are two tipping points. One that humanity is in danger of passing or which may even have already been passed. The other, which this question asks about, is nowhere near.

The one which has climate scientists worried is the runaway thawing of the planet's permafrosts with associated release of methane gas. It is a positive feedback loop and it is believed to have happened many times before. The result is an ice-free Arctic ocean, serious sea level rises from thawing of the Greenland ice cap, and probable temperature rises in the tropics making them too hot for human beings and other large mammals. Pretty catastrophic but life and even human life will go on.

The one which results in the planet turning into a version of Venus requires first that the Antarctic completely thaws. Thereafter any further increase in global temperature results in increased evaporation from the oceans, increased cloud cover, and greater reflection of solar radiation back into space. This is a negative feedback loop that stabilises surface temperature across a wide range of atmospheric CO2 levels. It's also the normal state of the planet through most of its geological history. The current situation, between ice ages, is both unusual and unstable.

The negative feedback stabilising a warm and ice-free earth has a limit. If cloud cover reaches 100% then the end is nigh. Water vapour is itself a greenhouse gas and the feedback turns from negative to positive. This is the probable fate of the earth as the sun grows hotter, quite a few hundred million years hence.

I don't know if we could trigger the end of all life by burning all the fossil fuels. The catastrophic effects of melting the Antarctic would probably put a very severe brake on all human activities, if the lesser effects of melting the Arctic had not persuaded us to stop burning stuff!


This may be naive, but ... all that coal and oil came from what was previously atmospheric CO2. This happened during the Carboniferous Period. So ... what was the climate like just before that, during the Devonian Period? Let's go look: https://en.wikipedia.org/wiki/Devonian .

If we burn up every scrap of oil and coal, wouldn't we end up with a climate similar to the Devonian? Which was unpleasantly hot (6C above modern level) but not unsurvivable.

Point being, and this is an honest question because I just don't know ... don't we already know there's no tipping point because these conditions have happened before?


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