Fortunately, air pollution is one of the easier things to put right, which we are doing by cleaner burning of fossil fuels. Unfortunately, this means that we have significantly underestimated the intensity of the greenhouse effect. The extreme predictions - melting of the Greenland ice sheet and release of methane hydrates from the ocean floor - would lead to the Earth being warmer than it has been for 4 billion years.
Of course, none of this is proven and should not in the least bit be taken as a warning to take any action that might harm the US economy. In which case, I suggest the US invests heavily in solar energy - as the removal of the global dimming effect could increase the intensity of sunlight at the Earth's surface by 20%.