According to a report from the US Energy Information Administration (EIA), US energy-related CO2 emissions decreased by 146 million metric tons (MMmt) in 2015 to 5,259 MMmt, down 2.7% from 5,405 MMmt in 2014. This decline occurred despite growth in real gross domestic product (GDP) of 2.6% as other factors more than offset the growth in GDP. Energy-related CO2 emissions in 2015 were about 12% below 2005 levels.
These factors included a decline in the carbon intensity of the energy supply (CO2/British thermal units [Btu]) of 1.8%; and a 3.4% decline in energy intensity (Btu/GDP). Of the four end-use sectors, only transportation emissions increased in 2015 (+2.1%).
Specific circumstances, such as the very warm fourth quarter of 2015 and relatively low natural gas prices, put downward pressure on emissions as natural gas was substituted for coal in electricity generation. The downward pressure on emissions was slightly offset by an uptick in transportation energy consumption that was influenced by lower fuel prices that put upward pressure on emissions. These conditions do not necessarily reflect future trends.—“US Energy-Related Carbon Dioxide Emissions, 2015”
Since the late 1990s, the transportation sector has produced the most CO2 emissions of the four major end-use sectors. These emissions were highest in 2007, prior to the recession, and have not returned to those levels, although they have increased since 2012. In 2015, the difference in emissions between the transportation and industrial sectors widened as transportation sector CO2 emissions increased while industrial sector CO2 emissions declined.
According to the EIA, the 2015 increase in energy-related carbon dioxide emissions from the transportation sector was led by gasoline.
The 28% decrease in gasoline prices (in nominal dollars) from 2014 to 2015, along with the continued economic recovery, led to higher fuel consumption. Transportation-related CO2 emissions increased by 38 million metric tons (MMmt) (2.1%) in 2015.
Gasoline accounted for 77% of the 38 MMmt increase in the transportation sector—30 MMmt, an increase of 2.8% from 2014 levels. Emissions from jet fuel, increased by about 5% (11 MMmt). Diesel fuel emissions, on the other hand, declined by 0.4% between 2014 and 2015.
Electricity. The trend of declining coal-fired electricity generation in the power sector and increasing non-fossil and natural gas-fired generation continued in 2015.
Coal’s share of total electricity generation in the power sector fell from 54% in 1990 to 34% in 2015.
The non-fossil electricity generation share, including both nuclear and renewables, in 2015 equaled that of coal at 34% in 2015.
The natural gas share of electricity generation grew from approximately 11% in 1990 to 29% in 2012, and to 31% in 2015.
Although nuclear power remains the dominant source of non-fossil electricity generation, growth in wind and solar generation since 2008 has also contributed to a decline in the carbon intensity of electricity generation.
The nuclear share of non-fossil electricity generation has generally declined since reaching 75% in 2001.
Hydropower, which historically has been the largest source of renewable electricity generation, has also lost share, falling from 34% of non-fossil fuel generation in 1997 to 19% in 2015.
Wind and solar (combined) accounted for about 17% of non-fossil electricity generation in 2015 after rising from less than 1% in 2000 to 2% in 2005.
Other renewables such as biomass have remained at about a 4% share.
In 2015, non-hydro renewable generation exceeded hydropower generation.