| Summary: |
Fossil fuel CO2 emissions in the U.S. decreased by about 11% between 2007 and 2013, from 6,023 to 5,377 Mt. This decline has been widely attributed to a shift from coal to natural gas in U.S. electricity production. However, the factors driving the decline have not been quantitatively evaluated; the role of natural gas in the decline therefore remains speculative. Here, we analyze the factors affecting U.S. emissions from 1997 to 2013. Prior to 2007, rising emissions were primarily driven by economic growth. After 2007, decreasing emissions were largely a result of economic recession with changes in fuel mix (e.g., substitution of natural gas for coal) playing a comparatively minor role. Energy-climate policies may therefore be necessary to lock-in the recent emissions reductions and drive further decarbonization of the energy system as the U.S. economy recovers and grows.
|
