In the final analysis the "concerns" of the majority of Americans is not the question (especially when those "concerns" have been artificially ginned up by partisan political actions) if the planet becomes unable to provide for its population.
You are right that it can't be done by the US alone. It must be an international cooperative effort. The current GOP and big oil is bound and determined to make the USA a non-participant as opposed to a leader and they are not above lying to do it.
The bottom line...warming fact, it may not be a major problem in most of our lifetimes, but it WILL eventually be a problem for everyone unless, at the optimum it is stopped or reversed and at minimum prepared and planned for. There is always the possibility it will correct itself but the world's people and their leaders would be very foolish to bet the future of billions on that happening.