> But the US is worse when it comes to CO2 emmited per capita. That means that US should also be taxed.
China - as all nations - has a responsibility based on its population scale (ie its total emissions output), not just its per capita output. The total output matters far more than per capita, as we're dealing with a matter of planetary survival, not whether it's fair that Monaco has higher emissions output per capita than China.
Other nations are not responsible for China having those 1.4 billion people. China bears that responsibility. Other nations are obviously not responsible for the US having its per capita emissions output, either.
Estonia having 4x the per capita emissions output of the US wouldn't pose a terminal risk for the planet. And sure, maybe it's fair to argue a tax to incentivize per capita behavior of high per capita emissions nations. And what to do about China's total output risk, given it's going to destroy the planet (whereas smaller nations do not pose that risk)? The logical thing would be to apply taxes to both, in a way the keeps the planet from getting destroyed: it means China can never be allowed to have parity with smaller nations that have high per capita outputs.
China, with its 1.4 billion people, would pose a terminal risk for the globe if it reaches per capita emissions output parity with the US (actually it's already approaching that risk now, and it's merely half way to parity). Taxes don't mean much if half the planet is wrecked. China has a different responsibility than Estonia does given China can all by itself destroy the world with its emissions. I use Estonia merely as an example to highlight the point, very obviously the US has a responsibility as well based on its scale. Sure, we can focus a tax in on Estonia in that case, however it's by far not our most pressing matter.
China going from ~28% of global emissions to ~45%, is a very pressing matter. The globe can't afford China to increase at all at this point.
If a country had four billion people, it similarly wouldn't be reasonable for it to reach emissions parity with the US: it would kill everyone in doing so.
The equation of fairness must also consider the scale of the threat being posed, as it's also not fair if one outsized population nation gets to destroy the planet because it has 1.4 billion people. One can live in fantasy (where fairness means every nation gets equal emissions output per capita), or live in reality. In reality it matters how many people you have and what their per capita emissions are. Reality is course the dimension where we can all die from the emissions output of a nation the scale of China.