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In my world, there's a global apocalypse that wipes out humanity, but I'm wondering how global warming might continue even with the lack of additional greenhouse gases. If emissions suddenly stopped, how much longer would climate change persist? What would the climate be like after 100 years? 1000? Would it have gone back to normal, or would the damage be irreversible for potentially thousands of years?

Edit: Some of you seem to be misunderstanding my question and why I've used the "hard-science" tag. My question has nothing to due with the circumstances of the apocalypse. I am asking what would happen if all man-made causes of climate change suddenly stopped, and how long it would take to go back to normal.

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    $\begingroup$ please ask one question per post. you may want to split this up into multiple posts. $\endgroup$
    – alkahest
    Mar 1 at 18:28
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    $\begingroup$ The problem with this question is. There is no "normal". Especially if you say "return to normal". For the greater part of the existence of life on earth bay far (not even close) primitive unicellular organisms that didnt even produce oxygen were the dominant life forms. So by the metric of normal as longest existing. We've been abnormal for the last 2.5 billion years. Perhaps find your start and endpoint to discover what you need to describe your setting. $\endgroup$
    – Gillgamesh
    Mar 1 at 20:04
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    $\begingroup$ What's with people on this site overcomplicating simple questions instead of using common sense? $\endgroup$ Mar 1 at 20:39
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    $\begingroup$ It's a simple question about an incredibly complex subject. Sort of makes it by implication a complex question. $\endgroup$ Mar 1 at 21:19
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    $\begingroup$ @Slarty the apocalypse is completely unrelated. $\endgroup$ Mar 2 at 8:48

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Contrary to most answers, I will refer to the authoritative source on the matter. Which is the IPCC, you can find all their reports here : https://www.ipcc.ch. if you are more broadly interested on this issue I highly recommend you read at the very least the summary for policymakers (couple of pages instead of thousands). There you can learn that it would take twenty to thirty years to stabilize the temperature after the cataclysm you describe. For return to "normal" it would take much longer "Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level." https://www.ipcc.ch/report/ar6/wg1/chapter/summary-for-policymakers/

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Climate is a chaotic system, with complex and mutually interacting feed back and feed forward cycles.

Small changes are reversible, larger not so easy. There is currently no agreement on what is small and large. According to certain climatologists we are close to the point of no return, according to others we are past it.

How long will the climate take to get back to normal or if it will get into a new normal is matter of scientific debate.

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Asking for when dealing with a fictional concept like an apocalypse, especially when serious amounts of time are involved, is a tall order. The Earth hasn't experienced an apocalyptic event for quite some time and humans weren't a significant factor during the last one. So I'm going to shift to . When you get a moment, read the wiki. Answers that don't adhere to its rules are under threat of deletion.

Climate change isn't 100% human-caused

And for your story, that's a good thing! The Global Temperature Record tells us that the Earth has a natural hot-to-cold cycle. As it turns out... humanity's impact came during a natural increase in temperature. In other words, we've successfully made something inconvenient into something ugly. So, to answer most of your questions, follow that link and look at how the temperature cycles work.

@Alkahest is right, asking multiple questions is literally a reason to close questions, but in your case you got lucky in that the "answer" happens to exist in a way to cover most of what you're looking for. Please don't trust in that, though.

As for how long the human component will last... nobody really knows. Human emissions don't drive global temperatures in the same way water in a river drives a water wheel. It will take time for the Earth to absorb excess chemistry from the atmosphere and to rebalance everything. Some areas will recover much faster than others. Recovering from desertification, for example, will take a while.

Desertification is the process by which vegetation in drylands i.e. arid and semi-arid lands, such as grasslands or shrublands, decreases and eventually disappears. The concept does not refer to the physical expansion of existing deserts, but to the various processes that threaten to turn currently non-desert ecosystems into deserts.

Human activities, including deforestation and the overexploitation of aquifers, accelerate desertification. The effects of climate change, which is also driven by humans, and the destruction it causes in the form of extreme weather phenomena such as droughts, hurricanes, fires, etc. must be added to this.

According to the UN, more than 24 billion tonnes of fertile soil disappear every year. In fact, today two-thirds of the Earth is undergoing a process of desertification and, if no action is taken, 1.5 million km2 of agricultural land, an area equivalent to the entire arable land of India, which is essential for maintaining biodiversity and feeding the population, will be lost by 2050.

Now, whether or not that 2050 prediction will come true is a good guess. I've been hearing claims like, "irreversible climate change in the next 5 years!" since the 1970s. Humanity has a long way to go to be good stewards of the Earth, but more are converted to the cause every year and better technology comes along with it. So it's unlikely that an area "equivalent to the entire arable land of India" will be desertified by 2050... but they're point isn't wrong in essence.

Therefore, if we use their statistic as a base, it's 2024. That means that area is expected to become a desert in 26 years. Humanity will have helped that along and the Earth can't provide the same kind of "help" in reverse, so it'll take longer than 26 years to recover once humanity stops.

The problem is, how long? We don't know — but that's good for you because it means you can use any "reasonable" number you wish. I wouldn't guess 1,000 years. But I'd believe hundreds.

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In the very short term humanity still is around.

In the short term, the gun https://en.m.wikipedia.org/wiki/Clathrate_gun_hypothesis fires.

In the medium term plant like organisms and there sinking corpses + errossion of stone rebind carbon dioxide. Over geologic times earth's climate waves and cools.

If intelligence does not reappear even phases of https://en.m.wikipedia.org/wiki/Snowball_Earth might even return, ended by asteroid strike caused volcanism.

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There is a simple way to think about this question. It has to do with the heat capacity of the oceans. When you add heat to water, its temperature increases. But how much energy will produce how much increase in temperature? That answer was known many years ago: it takes 4.19 Joules of heat to increase the temperature of one gram of water by one degree Celsius.

Now, at this point the calculation is nowhere near as straightforward as you would think, as you have to take into account mixing and evaporation, but it all boils down to a rough rule of thumb: it takes about 30 years for a small perturbation in the energy flow of the planet to reach equilibrium. This provides the answer to your question: if all human emissions of greenhouse gases stopped in 2024, the planet's temperature would continue rising until 2054. To put it another way, the climate change that we are experiencing today is the result of emissions going back as far is 1994

I emphasize that this is a gross simplification of some extremely complex calculations. The real lesson to learn is that climate change is particularly insidious because the people who do the damage probably won't live long enough to suffer the full consequences of their actions. Those consequences will be suffered by their children.

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While 3470600's 30-year estimate sounds about right, it doesn't represent the most extreme case scenario. And I'm assuming you are looking for the highest temperatures plausible. Because of feedback loops in the system, it is HYPOTHETICALLY possible that we have kicked off the conversion from an Icehouse climate to a Hothouse climate. As such we could then see the global temperature increase 9°F. Long after that it might rise to an average surface temperature of 68°F (the Icehouse-Hothouse threshold according to the graph over here), I have my doubts that any expert would estimate human-caused climate change to ever result in higher temperatures, but if you are writing a story I could easily believe the scales could be tipped so that in a couple of thousand years the surface temperature has reached 85°F (as it was in the [Pal]eocene Thermal Maximum).

However, if you really want to show a post-apocalyptic inferno in your story then there are plenty of other sources of global warming that could happen over the millennia. (You can find out more about the future of climate change on Wikipedia.) In fact, volcanic activity could raise the planet's temperature anywhere from 1° to that of Venus, (after all, Venus turned into Venus without extraordinary circumstances). Although the planet is probably too old to {alone} have enough volcanic activity to raise temperatures as it did 700 million years ago, a big ol' (radio-active) meteorite could probably give it back some pep.

P.S. I'm no expert I might be using the terms Icehouse and Hothouse wrong.

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