Don't forget that U.S has outsourced its industry to China. Just look at the current trade balance. It's all over the news now thanks to the trade war. And the reason it was outsourced is precisely because environmental regulations are weaker in China and therefore production is cheaper. And on top of that you add shipping emissions, which are not included in any country emissions.

Or 1/2 what the US outputs per capita, which is the more relevant figure since the atmosphere does not care about arbitrary political boundaries.

To be fair China is basically the factory of the world, manufacturing a lot of the gadgets that are mostly used in 1st world countries.

It's pretty clear that if the west consumed less China wouldn't pollute nearly as much. So yes, everybody has a choice, either be actively part of it or try to pollute as little as possible.

You're saying "the impact of one person is limited therefore no one should take action". I'd argue that everyone should take action, show the example in your home, local community, &c. Little by little people get more engaged, just look at the green parties in Europe, 20 years ago they barely got 1% of votes in elections, now they get >20% in some countries.