If the Earth's population was 1 billion, 10 billion, or 100 billion, but the emissions were the same, in each of those cases we would be cooked to death by our own atmosphere. Even though they have wildly different per capita emissions.
Or to put it a different way, if all I knew were the parts per million of carbon in the atmosphere, and all you knew were per capita consumption figures, I would know when the atmosphere was truly cooked and you wouldn't.
What's your point? This is not about "knowing if the atmosphere is cooked or not".
High emission countries/individuals are most responsible for the environmental damage, and most capable of reducing their emissions with the least impact on their living standard.
Or to put it a different way, if all I knew were the parts per million of carbon in the atmosphere, and all you knew were per capita consumption figures, I would know when the atmosphere was truly cooked and you wouldn't.