Dive Brief:

• Carbon dioxide emissions from the power sector have fallen below those from transportation, a reversal not seen in the United States since the late 1970s, according to data from the U.S. Energy Information Administration. 
• The EIA said the new analysis is based on emissions levels through September 2016 that was reported in the most recent Monthly Energy Review.
• While the electric power sector consumes more energy than the transportation sector, the carbon intensity of the power sector has fallen much faster than the transport sector due to increasing amounts of natural gas, hydropower, wind and solar coming online. 

Dive Insight:

It's been almost 40 years since carbon emissions from the transportation sector were greater than power generation, but a confluence of economic and technological factors have switched the two. EIA's data appears to verify predictions in a University of Michigan study, which said cheaper oil would boost sales of gasoline-dependent trucks and SUVs, consequently increasing emissions for transportation. 

That study also pointed out that as coal lost ground to natural gas and renewables, power sector CO2 emissions dropped on average 2.8% a year between 2007 and 2015. Conversely, carbon emissions from the transport sector increased at an average rate of 1.8% per year over the past four years as increased travel and shipping outpaced efficiency gains.

According to EIA's data, CO2 emissions from transportation were 1,893 million metric tons (MMmt) from October 2015 through September 2016, compared with the power sector's 1,803 MMmt.

The agency primarily credited the decline in coal burn, which is the most carbon intensive of the fuels. According to EIA, coal combustion on average emits from 206 to 229 pounds per million British thermal units (lbs CO2/MMBtu), depending on type. For gas, combustion emits 117 lbs CO2/MMBtu. Gas generators "also tend to be more efficient than coal generators," EIA noted.

Transportation emissions tend to fall in between coal and gas, with gasoline emitting at an average rate of 157 lbs of CO2/MMBtu. Motor gasoline represents about 60% of transportation emissions.

While coal and natural gas had "nearly equal shares of electric power generation" from October 2015 through September 2016, their shares of electric power sector emissions were 61% and 31%, respectively, according to the EIA. "Overall electric power carbon intensity has also decreased as generation share of non-carbon-emitting fuels such as nuclear, hydropower, wind, and solar has grown," the agency said.

But 2016 also saw a slew of coal retirements as utilities moved to replace an aging coal fleet with cheaper natural gas. Carbon regulations played a part, as roughly 30% of the coal retirements occurred after the U.S. Environmental Protection Agency's Mercury and Air Toxic Standards rule went into effect in 2015.