The atmosphere doesn't care about political boundaries either, so there's not much utility in drawing a line around an arbitrarily large group of people and sum

The atmosphere doesn't care about political boundaries either, so there's not much utility in drawing a line around an arbitrarily large group of people and summing their emmissions. The only reason to look at country-level stats at all is to assess the effect of policy, and controlling for population size is the correct approach for that comparitive analysis.