The electric power sector emitted 128 million metric tons of carbon dioxide (MMmt CO2) in April 2015, the lowest for any month since April 1988, according to the most recent estimates in EIA's Monthly Energy Review.
In any year, April is typically the month power plants emit the least carbon dioxide, mainly because of mild weather, as low heating and cooling demand are reflected in low overall electricity demand.
Two fuels, coal and natural gas, account for almost all the carbon dioxide emissions from the electric power sector. In April 2015, electricity generation from both coal and natural gas fell from their March values, but because coal fell more than natural gas (18 percent versus 6 percent, respectively), generation from natural gas surpassed generation from coal in April.
The consumption of the primary fuel, not necessarily the amount of electricity generation, is the appropriate metric from an emissions perspective. Because natural gas plants are now about 25 percent to 30 percent more efficient than coal plants (in terms of heat rates, or the energy content needed to produce a unit of electricity), coal's share of coal and natural gas energy use for power generation exceeded its share of combined generation. Despite lower generation, use of coal for power generation exceeded use of natural gas for that purpose in April.
The two fuels also have different carbon dioxide emissions intensities. Generating electricity from coal produces 71 percent to 79 percent more carbon dioxide emissions than generation using natural gas. In April, consumption of natural gas in the electric power sector accounted for 36.4 MMmt CO2, while coal use accounted for 89.4 MMmt CO2.
Beyond coal and natural gas, more electricity is being generated from sources that do not release carbon dioxide as part of the generating process. Nuclear power generation increased 3 percent for the first four months of 2015 compared with the first four months of 2014, as fewer nuclear units entered planned or unplanned maintenance.
Renewable energy generation increased by 2 percent over the first four months of 2014. Although wind generation fell 7 percent because of relatively low wind resources, hydroelectric generation, which accounts for about half of all renewable energy in the electric power sector, increased 7 percent.
A longer historical perspective shows larger changes in the electric power sector fuel mix. Comparing April 1988 to April 2015 (27 years), natural gas consumption in the sector more than tripled, renewable energy consumption more than doubled, nuclear energy consumption increased 47 percent, and coal consumption decreased 17 percent.
Electricity generation has become less energy and carbon intensive over time. Compared to April 1998, April 2015 generation in the electric power sector was 44 percent higher, but the associated primary energy use and carbon dioxide emissions increased by only 33 percent and 4 percent, respectively.