U.S. carbon dioxide emissions declined last year to their lowest level since 1994 and more than 12 percent below the recent 2007 peak, according to data released yesterday by the Energy Information Administration.
Since 1990, only 2009 saw a larger percentage decrease in emissions than 2012, the EIA said.
The decline occurred in tandem with an increase in gross domestic product and an increase in energy output. The combined reduction in energy use per dollar of GDP and the carbon intensity of the energy supply meant that the overall carbon intensity of the economy (measured by carbon dioxide per unit of GDP) declined 6.5 percent in 2012, the largest drop in the overall carbon intensity of the economy since records were kept beginning in 1949.
The residential sector was the largest contributor to the decline in 2012, with the help of an unseasonably warm first quarter resulting in reduced energy use.
By the end of March, cumulative heating degree days -- a measure that indicates when the mean temperature was cold enough to likely require heating buildings -- were about 19 percent below the 10-year normal and 22 percent below 2011, according to the EIA.
And on top of a decline in residential energy use, the EIA also noted a 4.8 percent decline in electricity system losses, "implying an efficiency increase in electricity generation, transmission and distribution."
The transportation sector was the next biggest contributor to the 2012 emissions decline. Vehicle miles traveled remained flat from 2011, but more energy-efficient vehicles entered the market. Thus, vehicle fleet efficiency improved 16 percent between 2007 and 2012. Transportation sector emissions in 2012 remained well below the comparable level for 2007 in each month over the year.
Natural gas up, coal down
Given its 2012 surge, natural gas also had a big hand in the 2012 decline in emissions, principally because of its lower carbon energy intensity.
As natural gas has boomed, the EIA report found, there has been an overall decline in renewable power generation, with hydropower seeing a drop of almost 50 billion kilowatt-hours in 2012. Wind, however, saw a slight uptick of 20 billion kWh last year, while coal power generation plummeted by 215 kWh.
Industrial output was 2.7 percent lower in 2012 than in 2007, and manufacturing output in particular was 5 percent below the 2007 value.
In its report, the EIA concluded that it was difficult to draw conclusions for future emissions based on one year of data but that some variables, including improvements in vehicle fuel efficiency and increased use of renewable generation, "could play a continuing role in subsequent years."
The EIA also noted in its "International Energy Outlook" report for 2013 that natural gas will be the world's fastest-growing fuel through 2040 (EnergyWire, July 26).