The bulk of the USA's GHG's come from burning coal for electricity. Jimmy Carter mandated the US switch to coal in 1977, because of the energy crisis. By coincidence at the same time a concerted and sustained effort was put out by the 'environmentalists' and their supporting democrats, to stop new hydroelectric and nuclear power plants under construction, and halt new starts of either.
This quite by chance left Coal with no real competition that did not require government subsidies (wind, solar, biomass) to survive. As`a result we burn LOTS of coal. It's probably fair to say our GHG emissions are really unnecessary and entirely self made problem because of the energy infrastructure that resulted from Democrats response to environmentalism and the energy crisis. Whats the best way to reduce GHG emissions? By rebuilding the infrastructure. We can vastly improve our efficiency, reducing ALL pollution, end the energy crisis, keep our cars mostly as we like them, end our water problems, stop most GHG emission, and make and save a lot of money in the long run!!! Except that would bring competition to coal.