Energy-related carbon dioxide emissions have declined in the United States in four out of the last six years. Emissions in 2011 were 526 million metric tons (9%) below the 2005 level.

The industrial sector experienced energy consumption growth of 0.7% in 2011. The commercial sector fell slightly (0.3%). Energy consumption in the residential sector fell by 1.1% and in the transportation sector by 1.4%. The sum of these sector changes meant that total energy consumption fell by 0.5 percent—this coupled with economic growth of 1.8% meant that the energy intensity of the economy fell by 2.3%.

Factors influencing the decrease included:

• In 2011, transportation-related carbon dioxide emissions fell primarily due to higher fuel costs, improvements in fuel efficiency, and a reduction in miles traveled.

  In 2010, the price of regular gasoline averaged $2.78 per gallon. In 2011, the average price rose to $3.53 per gallon—an increase of 27%. It is estimated that the miles per gallon (mpg) of light duty vehicles improved by 1.0% (20.4 to 20.6 mpg) from 2010 to 2011. Vehicle miles traveled fell from an average of 8,127 million miles per day in 2010 to 8,029 million miles per day in 2011 (1.2 percent).

  This contributed to a decline in gasoline consumption of 2.9% which, in conjunction with changes in other transportation fuels, resulted in a decline in total energy consumption in the transportation sector of 1.4%.

• In 2011, cooling degree-days (CDD) were slightly higher than in 2010 (0.7%). This would tend to put upward pressure on electricity demand and related emissions. On the other hand, heating degree-days (HDD) fell by 3.2% and residential sector energy consumption declined by 1.1%.

• A carbon intensity decline in the electric power sector (-4.0%) which accounted for 40% of total U.S. primary energy use in 2011, helped achieve the lower carbon intensity of the energy supply. Because primary energy use in the electric power sector is allocated to the end-use sectors based on their share of electricity use, the drop in reported carbon intensity for the end-use sectors was greatest in the residential and commercial sectors (3.1% and 3.2%, respectively) as these sectors rely heavily on electricity to meet their energy needs.

• Since 1949, the 2011 decline in coal generation of more 6% is second only to the decline in 2009 of almost 12%. As recently as 2005, coal’s share of electric power sector generation was more than 51%. By 2011 that share had declined to just over 43%. Petroleum generation, which was small to begin with, has also lost share. Natural gas, on the other hand, has steadily grown in market share. The introduction of new, efficient gas-fired capacity and a recent decline in the price of natural gas has helped boost natural gas’ share from 14% in 2000 to 24% in 2011.