"vastly" is well out of place here.
Currently, on a per annum basis, China is the number one emitter, the United States is number two. China currently puts out ~ 2.5 the total of the US.
* less than 3x is hardly "vastly more"
* on a per capita basis China emits less per person than the US.
* Much of China's emissions are due the US offshoring manufacture, a large chunk the CO2 rising from China is a result of US consumer demand.
Moreover, the current yearly outputs are merely the bleeding edge of the CO2 problem - it's the cumulative total that is responsible for the increased insulation that is trapping an increasing amount of heat energy.
On that front the US is responsible for more of the total raised by human activity than China.
By country, per year: https://www.worldometers.info/co2-emissions/co2-emissions-by...
By country, cumulative total: https://ourworldindata.org/grapher/cumulative-co-emissions