If humans survive for millions of years we'll almost certainly transform the planet vastly further than anything even conceived of so far (except perhaps in SciFi). And I wouldn't assume that even within a few 1000 years Earth will be more habitable than elsewhere (but yes, it's almost guaranteed for the next century or so at least). OTOH, if we really did somehow totally self-destruct as a species, there's good reason to suppose the climate would settle back to something similar to what it has been the last 10k years, though it certainly won't last forever, or even much more than a dozen or so more thousand years.

No, it's too late, we won't ever get back to last century climate, Oxydes are some of the most stable molecules on earth, so the only way to get them out of the mid to high troposphere (where it actually have an impact) is to lower their concentration in the low troposphere.

At the moment, the CO2 you emit will take roughly 20 year before it has an impact on climate (the time to reach the altitude necessary for the re-emission to cause real harm). When we start planting trees and let the ocean capture the Co2 (they will acidify, but fuck the plankton and corals at that point, we can't do anything about that), then it will start to get better. It will take roughly five hundreds years to eliminate half of our past an current emission (if we stop in 2050) and ten thousand to get back to 1850 climate.

So, yeah, it will settle back, but in a long, long time.

Fucking the plankton isn't a good idea when the phytoplankton absorb 40% of all CO2 emissions.

Source: https://en.wikipedia.org/wiki/Blue_carbon

It won't fuck the phytoplankton that much, it is the zooplankton that will suffer (and yes, this will have effect on the phytoplankton, but like I said in another comment, consequences are too hard to evaluate.

10 thousand years is a little longer than I was thinking, but OK - it's a lot less than the millions mentioned by the GP.

Think of it as the half life of CO2 being 500 years (that's not that, but the curve is similar). The climate in 5000 years will be sufficiently similar to the one in 1850 for everything to settle back.

Except to be honest, we're not sure. The ocean will also probably reemit in the atmosphere some CO2 it is capturing right now (becoming less acidic), so with absorption slowing down, we're not sure how it will go. We know that it will need at least 10 000 years to get back, but we might ignore other phenomenons. Maybe bigger (so higher) Cyclones will accelerate the time needed for the excess CO2 in the high tropsphere to come down.

The sad, harsh and i guess also beautiful thing about this climate change event is that it is a full-scale experiment that have never been done before, that will change everything and on which we don't have enough theories to predict exactly what will happen.

CO2 levels, maybe. But it won’t bring back the extinct species or drowned cities.

No, but there's every reason to expect there'd be an explosion of new species. I'd much rather that happen while there are humans around to witness it of course but I'm not sure if we deserve to.

> there's good reason to suppose the climate would settle back to something similar to what it has been the last 10k years

What's that good reason?

My understanding is that the natural CO2 cycle would gradually remove the excess concentration currently in the atmosphere. I don't know how long it might take, several centuries at least I suppose.

Other than the easily available fossil fuels, this planet will be essentially back to the wild state a few tens of millennia after a hypothetical catastrophic collapse in technology.