I know the UK has a lot of wind and solar, and then there's short transport distances: those other countries are famous for hauling goods over long distances through sparsely populated terrain, which the UK doesn't have any of.

I wonder which country is considered to own the emissions from a cargo ship?

But anyway, about China, we agree on one thing: there are a lot of Chinese who are pretty much not participating in emissions. Then there are cities, factories, power stations for factories, and the government which, and this is the important point, has control over those sources of emissions.

If you split it into two nations, what that does is to remove the single point of control, and as a result remove the opportunity to do something about a huge portion of global emissions. Politically speaking splitting China in two sounds like an improvement, and lots of fun, but if you want some entity to control a really large amount of emissions, it's surely a giant authoritarian state that has the power to do it.

If the two halves were different in industrialization - if one had all the peasants and the other had all the factories and factory workers - that would help, since then you have a country that tops both lists, and can be firmly blamed by everyone, and we can stop getting lost in the weeds of "per capita" and the mad idea that individual scum like me and you have any responsibility to solve climate change by reusing plastic bags and so on.