> who would it make more sense to go after first
Both as the effect is global, and if the differential is 2:1 both have much room for improvement. Though you must not conveniently forget that much of China's emissions stem from being the world's manufacturer. A hell of a lot of European and US emissions have been globalised to China, rather simply a billion Chinese adopting a Texan lifestyle. I'd be interested to see per capita global emissions after someone accounted for globalisation of manufacturing and services, and brought all those imports back home, emissions wise.
Yet even after outsourcing all that heavy industry and manufacturing, the US has, by far, the worst per capita emissions on the planet. It is completely beyond my understanding when numbers sometimes come up on HN, how they are able to use so much for a family. The lifestyle isn't 2x UK, France or Germany. Not just CO2, but water use too. It beggars belief to be so wasteful for so little gain.
Everyone should be doing more, whether tiny or the largest. It really should be a race to the bottom - for national, and global pride.
I'd encourage you to harass my country all you like - decidedly mid tier on climate action and emissions, precisely because they are mid tier on a globe that is not doing nearly enough. Complaining it's worse elsewhere just reeks of trying to evade or ignore the issue.