To be the devil's advocate, the deniers will say "We've been emitting CO2 since the beginning of the world, and it's been fine, why are you worrying now?" - yea

To be the devil's advocate, the deniers will say "We've been emitting CO2 since the beginning of the world, and it's been fine, why are you worrying now?" - yeah sure that's ignoring the fact that there are now more cars, more planes, more factories, more cows, etc, but that's to be expected of these unscientific people.