I think I have heard that if the carbon emission raises a small amount above the current, it would be "point of no return". I heard it a long time ago, so I just searched Google and the top article says "irreversible damage".
But when I searched Google for a graph of historic CO2 levels, there was something like the one below. Granted that this was not the top search result (the top one was not continuous), but if this graph is correct, the CO2 level has been historically much higher than now. If there is any irreversible damage, won't that have already happened? And the CO2 level seems to be able to go down once it has risen, so it does not seem that the current CO2 level cannot get lowered once a certain level is reached.