ATTP, in Climate change doesn’t work like that, makes the conventional "the streets will be yards deep in horse shit" mistake: "On our current trajectory1, atmospheric CO2 will remain above 400ppm for thousands of years, and won’t return to pre-industrial levels for 100s of thousands of years". Of course, this is only true if nature takes it's course, which (assuming our industrial civilisation survives the next 100 years, which in itself seems very likely) is very unlikely. If we get that far, pulling CO2 out of the air is very likely to be possible in 100 years, and almost undoubtedly possible in 1000 years; so speculations as to CO2 levels thousands of years into the future that ignore human influence are pointless.
Notes
1. Of course he doesn't mean "current trajectory"; if we follow that, CO2 will continue increasing from our emissions; he means, "even if we stop emitting in ~2050 and then allow levels to naturally decline" I think.
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Of course he doesn't mean "current trajectory"; if we follow that, CO2 will continue increasing from our emissions; he means, "even if we stop emitting in ~2050 and then allow levels to naturally decline" I think.
I was mostly meaning that if you consider the current estimates of what BAU might be (such as those presented by Zeke Hausfather and colleagues last year) then we're probably heading for something like RCP6 and then atmospheric CO2 would probably remain above 400ppm for about a thousand years, or so. If we do better than that, as we may well do, it may drop below 400ppm slightly sooner.
You're right, of course, if we can find ways to artificially draw down atmospheric CO2 then we'd bring it down below 400ppm much sooner and, as long as the impacts aren't so severe that we end up without functioning economies, we would probably do so.
I have read that oceans are going to stay acidic for tens of thousands of years even with pulling CO2 out of the atmosphere.
Also, can we be sure that civilization survives long enough to do that?
I'm assuming civ survives, as I said. I think it likely. Indeed, I'd put money on it ;-)
Ocean acidification is a genuine problem too. But you get the same or a similar answer: if we survive for long enough, we'll work out how to do it. Or at least, I think that's a good first-guess. My point is not to minimise the problems, but to argue that we should primarily worry about the next 100 years; consequences beyond that are too uncertain to be worth worrying much about. See-also Should we care about the world after 2100?.
I think there are grave risks to disrupting nature on the scale we are doing. We just don't know how or when they may manifest - sea level rise is the clearest of these and it's pretty murky. But just because we can't imagine nature's revenge doesn't mean it isn't lurking out there.
Regarding civilization, the question in my mind is not whether it will survive, but whether it will begin.
On recent evidence, we have achieved a great deal more technical advancement than civilization sufficiently robust to manage it. The current greenhouse gas trajectory is only a part of the compelling evidence.
This all said, if we were only in some way collectively sane, yes, we could solve our problems.
> grave risks to disrupting nature on the scale we are doing
Indeed. I trust I have said nothing to give any other impression.
> whether it will survive, but whether it will begin
That makes a good soundbite, but not sense. We have civ; we have had it for 10,000 years or so. Only if you redefine the world to include "the wisdom to do X" do we not have it.
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