Sure, if you're talking per capita, US people emit more carbon dioxide but with your "even with 1/5th" and "the biggest polluter" it suggests you're thinking total not per capita.
The US were for a long time. But now it’s China. Although they already are the biggest producer of green energy world wide. They produce more green energy than all other countries combined. I don’t know if their strategy will drastically reduce their carbon emissions soon, for now they are still rising. In Europe and the US they are going down a while already (also because we moved a lot of our industry to china).
Yes, it's impressive what they are doing. But I think their total amount of carbon emissions are still rising in total. So their energy consumption seems to grow faster than their green energy production.
https://www.statista.com/statistics/271748/the-largest-emitt...
Sure, if you're talking per capita, US people emit more carbon dioxide but with your "even with 1/5th" and "the biggest polluter" it suggests you're thinking total not per capita.