What's the crux of your point here? I think you're imputing some wider meaning to what was actually a very simple point (i.e. saying that N people have no power, just because 1/N people can't individually make a difference, is like saying the electorate has no power over an election result because one of them can't change the outcome).

My wider point is precisely that people have personal responsibility for carbon emissions, in exactly the way you described. In the car example you gave, the "corporations are responsible for most of climate change!" argument would attribute the emissions involved in manufacturing your car to the corporation instead of you. It's a compelling argument until you think about it, in concrete terms like that, for even thirty seconds.