Well, surely the CO2 level itself could be reversed. But what other elements of the system's equilibrium will be changed in the meantime.
For example, the actual amount of temperature increase observed is less than the CO2 level increase would suggest. Suppose that whatever agency has tempered the temperature increase has "woken up", and continues to do so as CO2 decreases. Then a return to "proper" CO2 levels (if you can call any level proper) would mean serious global cooling. And this might not be evident until it's too late.
Of course, I'm making that up, but there's no reason to think that it's implausible.
> Suppose that whatever agency has tempered the temperature increase has "woken up", and continues to do so as CO2 decreases.
Why is that a reasonable thing to suppose?
We're assuming that we got to here from there before. Why is it reasonable to assume that we can't do so again?
Yes, maybe something else has changed, but shouldn't you at least go to the trouble of identifying actual possibilities instead of just assuming that they exist?
There are any number of processes that will occur easily in one direction, but can have... dramatic... results in the other direction. Consider, by analogy, breaking H2O into hydrogen and oxygen, vs. recombining them. Or, for more fun, consider a girl wearing a skirt, jumping on a trampoline. The process of going up is ordinary, but what happens on the way down is quite a bit different.
It's easy to dream up scenarios in the environment that might work this way. Algal blooms that have been pushed along by increased CO2 will affect the equilibrium between other types of sea life -- plankton up the line through large predatory fish. Moving up the food chain, creatures use input food less efficiently (carnivores need to kill much more food by mass than bunnies). So the algae enables plankton, which in turn feeds mackerel which in turn enable more sharks, but turning it around, as the algae recedes, the mackerel are pressured by the already-larger shark population, so they may well be decimated by the CO2 decrease. (I don't know if this specific example is correct -- it’s certainly oversimplified -- but the concept is certainly conceivable).
Reiterating: it’s very complex, we don’t really know.
> There are any number of processes that will occur easily in one direction, but can have... dramatic... results in the other direction. Consider, by analogy, breaking H2O into hydrogen and oxygen, vs. recombining them.
Ooh, dramatic. Except that the issue is irreversible.
You can split and combine hydrogen and oxygen repeatedly and the same thing happens every time.
We don't see evidence of dramatic effects from the last time CO2 levels were high and went down. (We also don't see evidence of the predicte runaway temperatures either, but I digress.)
If you're going to argue that this time will be different, shouldn't you have something better than "we don't know"?
Yes, we might see species changes. However, niches don't stay empty. And, the claim was "irreversible temperature changes".
> Yes, we might see species changes. And, the claim was "irreversible temperature changes".
Ahh, I think I expressed myself badly. I didn't mean that temperatures could return, period (although on second reading, my text does convey that). I meant that things couldn't be reversed as in a movie being played backwards, returning things to their original state.
I think we're actually in agreement, but talking past each other due to my poor initial phrasing.
> I meant that things couldn't be reversed as in a movie being played backwards, returning things to their original state.
Even if aliens took all of the "excess" CO2 out of the atmosphere tomorrow, manipulated the climate so it was always 1969 weather-wise (because that's the definition of perfection), and gave us an endless supply of dilithium crystals, things 10 years from now would be different than they are today.
Change always happens. The relevant question is good vs bad. (I don't see how one can assume that new species will necessarily be bad.)
For example, the actual amount of temperature increase observed is less than the CO2 level increase would suggest. Suppose that whatever agency has tempered the temperature increase has "woken up", and continues to do so as CO2 decreases. Then a return to "proper" CO2 levels (if you can call any level proper) would mean serious global cooling. And this might not be evident until it's too late.
Of course, I'm making that up, but there's no reason to think that it's implausible.