The McKinsey report cited below finds that the US can reduce it's emissions of GHGs 3- 4.5 GT using technology that is largely in place. "Eighty percent of the reductions come from technology that exists today at the commercial scale," director Jack Stephenson says. The other 20 percent is from technology that is currently being developed. Predicts that mitigation per ton of GHGs will cost less than $50 per ton. One main reason is that we waste large amounts of energy we produce, so simple changes could make the country vastly more efficient. We currently emit 7.2 GT, which is projected to increase to almost 10,000,000,000T (9.7GT) by 2030. If we reduced according to what they say, we would be at 5.2-6.7 GT by 2030. 1990 levels are 6.1GT of GHG emissions. Their analysis finds that there is potential by 2030 to reduce greenhouse gas emissions 35% compared with 1990 levels, necessary to keep warming below 2 degrees celsius as recommended by IPCC.
McKinsey and Company, Pathways to a Low-Carbon Economy, (New York: McKinsey and Company, 2009)