This is a difficult one. The selfish behavior of Americans does seem to be causing a real world crisis. Per capita, a few countries (the middle east and the US) produce significantly more CO2 emissions per capita than the rest of the world [1]. This is expected to cause everyone significant problems and is already taking a major toll on the forestry and fishing industries. Theres not a lot that the rest of the world can do to put pressure on the US. A war would only create more polution and wars suck. Trade embargos are difficult given the US's geopolitical possition. This may well be, in the end, a tragedy situation of game theory in which everyone loses and there is no way out. There is no real way to privatise the atmosphere to get rid of the tragedy of the commons going on there.
It actually kind of reminds me of the old "nuclear deterent" theory. The idea that if you attack me, I'll create nuclear armagedon. If there was a way for Germany to produce so much CO2 that everyone would die, then maybe Germany could tell the US, "if you don't stop producing CO2, we'll produce a lot of it ourselves". Really, I don't know though. So far, I'm not optimistic.
[1] https://en.wikipedia.org/wiki/List_of_countries_by_carbon_di...
