If the internal combustion engine only produced CO2 it might not be such a bad thing but you and I both know there's more to it than that, for example CO, Nitrous oxide, fine particulates, volatile organic compounds, and depending on the source of the fuel sulphur compounds. And then there's coal with all of the above plus mercury. As for what else has been predicted you can read as well as I can.  Oh, and thanks for proving my initial point.