Burned fossil fuels has well understood isotope signatures and can also be measured via satellite. We've got a LOT of data that human emissions of CO2 via burning fossil fuels accounts for the bulk of CO2 increase we measure in the atmosphere.
> I also know for a fact that other countries are much worse offenders when it comes to Carbon emissions and pollution in general, compared to the US or any other Western nation.
The problem is that this is a tragedy of the commons situation. For every individual actor, taking action is detrimental because the cost is paid by the individual but the benefit is broadly distributed over all actors. Tragedy of the commons type situations can be overcome by some sort of binding legal framework. This is why no one is proposing for any single country to solve the problem alone, but rather to coordinate internationally.
As a side point, morally speaking western nations have a particular responsibility because they are the ones who caused most of the increase in CO2 levels since industrialization. True, China is the biggest emitter now, but that is a fairly recent development.
But I disagree on some core orthodoxies. I think the root cause is deforestation / removal of carbon sinks, and a even lower-level root cause is simple human overpopulation. The amount of missing biomass from trees over the last few hundred years tracks very neatly with CO2 levels, as does of course human population levels.
I also know for a fact that other countries are much worse offenders when it comes to Carbon emissions and pollution in general, compared to the US or any other Western nation. Therefore, I don't understand nor support most US policy changes to "combat" climate change... I think these are at best a farce, and at worst cynical money grabs by professional fleecers.
How exactly is any US policy going to stop a poor farmer in Brazil from cutting down trees to make money to support his family? How will any US policy prevent the other 4 Billion or so impoverished people who are doing similar things?
As far as stopping China from polluting, we probably can't do much better than the effect Trump's tariffs have had, and are continuing to have... but Heaven forbid you tell anyone that who proclaims to care about the environment.