Eh - I don't think people think things through. Follow me here.
It has taken 2300 million years for life on this planet to suck hydrocarbons from the atmosphere and bury them (in the form of things like oil, coal, natural gas).
Now, we're digging it up, combusting it and putting it back into the atmosphere.
So we're no so much heading towards the tipping point, as rolling back the atmospheric odometer. If we keep at it, eventually the only thing that will be successful on this planet are anaerobes and cyanobacteria. In essence we're reversing the great oxygenation event. The world will eventually come to resemble how it looked during the early Palæoproterozoic period. Which is to say, there will be little to no advanced life and bacteria will be the top of the food chain.
And here's the kicker - the life that lived during that period is thawing out from the melting ice caps and waking up. What do you those nasty hydrocarbon rich bacterial and cyanobacteria blooms are that are floating along the coast of Alaka and other near arctic coastlines? They're the past re-emerging to reclaim the planet as we provide them with a viable habitat. On the upside - I bet they'll eat plastics like the Andromeda strain. hahahaha Another upside, I have no doubt that among the stuff frozen, but still alive and waking up in melt water of the ice cap are plagues the like we've never seen. Ok - those are downsides if you don't get sarcasm. ;)