For it to emit the majority they would need to emit more than 50%.

What you mean is that they are the country that currently emits the most. Although if we look for cummulative CO2, the US wins by a lot, then it is the European Union and then China. This matters because the C02 that is warming up the environment is not just what we emmit every year, but what we have emmited over all.

China is currently the main emissor, and they do need to do something about it (and they are doing it by being the biggest clean energy producer), but let's not forget that they are the second most populated country in the world and that they manufacture products for the rest of the planet too. The US, in comparison with only a small fraction of their population, pollutes too much.