450 ppm is a stretch goal and would require average global emissions over the century to drop more than 1/3 below current emissions.
In the scientific community, genuine climate change skeptics are vastly less numerous than those who see sufficient evidence to support immediate action to address climate change.
Reduction of vehicle emissions of carbon — through more efficient vehicles, mass transit, car pooling, cycling, etc. — also reduces all other forms of air pollution associated with vehicle exhaust.
Long before global warming began to be recognized as a major threat, we had compelling reasons to end our economic dependence on burning of fossil fuels.