Didn’t Hansen state that burning all coal and oil sand would do it? I‘m always wondering how much methane is assumed to be mixed in, as the amount of methane to be released is poorly understood as pointed out above.
Sorry, I should clarify: Hansen's paper indicated that burning all fossil fuels would create a 16 degree C warming, which would definitely be the end of the line for us, for reasons of heatstroke if nothing else, but in the same paper he does say that the temperature can't go up to Venus levels. So nature would eventually recover.