It doesn't matter how quickly we put carbon in the atmosphere. It has a 200 year effect - taking 60 more years versus 20 is meaningless if you end up putting it all up there anyway. The only difference would be how soon we suffer the worst effects - it's too fast for adaptation in nature for most evolutionary or migratory processes either way. I suppose you could hope for a technological silver bullet but that's effort made while dealing with a much more costly carbon economy.
Also, we should really avoid the worst effects. Even the middling effects are pretty awful.
Also, we should really avoid the worst effects. Even the middling effects are pretty awful.