"How many cars are there in the US?
In 2020, there were 286.9 million cars in the US. While car sales for the past few years arenâ(TM)t a simple upward line, other factors such as increasing car age and the need for personal mobility means amid the pandemic are making sure that the number of US cars is more or less progressively increasing."
So while it may the 3rd largest, that's about 8% the co2 put out by passenger automobiles.
And *all* transportation is about 30% of carbon emissions. So 23 million cars is one of what I call "american" measurements. We have a tendency to measure things in football lengths or other objects instead of saying a concrete fact like "Globally, all transportation emits 11.9 gigatons per year of which passenger vehicles emit roughly 7.14 gigatons".
And since the U.S. is about 15% of passenger co2 emissions, that would be about 1.05 gigatons and since this is about 8% of the U.S. fleet, that's about 0.084 gigatons of global carbon emissions.
But that's just a very rough estimate. I'd give it +/- 50% so 0.05 to 0.12 gigatons.
For comparison, humans put out roughly 119,426,010,658,613 stone of carbon per year.