The amount of energy-related CO2 released into the atmosphere by per unit of U.S. GDP produced fell 2.4% in 2001, or 136 million metric tons, while GDP went up by 1.8%. That means that the carbon intensity of the U.S. economy declined by about 4.2% in 2011. This is 9% below the energy-related carbon dioxide emissions level of 2005, or 526 million metric tons less. This is by no means a huge victory, and the atmosphere doesn't care about relative measures, all that matters is absolute numbers (the megatons of carbon rather than the percentages), but it's always good to see things move in the right direction. It'll have to accelerate a lot and continue for a while for the U.S. economy to de-carbonize its energy sector.
The industrial sector experienced energy consumption growth of 0.7 percent in 2011.5 The commercial sector fell slightly (0.3 percent). Energy consumption in the residential sector fell by 1.1 percent and in the transportation sector by 1.4 percent. The sum of these sector changes meant that total energy consumption fell by 0.5 percent – this coupled with economic growth of 1.8 percent meant that the energy intensity of the economy fell by 2.3 percent.
Of course, the U.S. doesn't exist in a vacuum. What truly matters is greenhouse gas emissions for the whole planet. So while the U.S. has been doing better, it has also moved a lot of its manufacturing to places like China, where CO2 emissions have risen considerably in the past decades. Macro-economic factors also need to be taken into account. Since 2008-2009, global economic activity has been reduce by one crisis after the other. This is all the more reasons to redouble our efforts and transition to low-carbon sources. How? I like the Reinventing Fire plan by Amory Lovins and the RMI.