According to new EPA data, transportation became the largest source of greenhouse gas emissions in the United States in 2017 after emissions from electricity generation continued to decline.
Of total greenhouse gas emissions, the majority are due to CO2 emissions. CO2 was responsible for 82% of all greenhouse gas emissions in 2017. Transportation accounted for 37% of total CO2 emissions. According to the report, the largest sources of transportation-related CO2 emissions were passenger cars (41%), medium- and heavy-duty trucks (24%), and light-duty trucks (17%). Commercial air travel accounted for a relatively small share, at 7% of transportation-related emissions.
An increase in travel was the reason transportation eclipsed electricity to be the largest source of CO2 emissions. The total number of miles driven by passenger cars and trucks increased 46% from 1990 to 2017.
Emissions from electricity have been declining, but electricity generation is still a significant source of CO2 emissions. According to the most recent EPA report, “Electricity generators used 32 percent of U.S. energy from fossil fuels and emitted 35 percent of the CO2 from fossil fun combustion in 2017.” This is influenced by the mix of energy sources used to generate electricity. While some electricity is generated from sustainable sources such as hydroelectric, solar, or nuclear energy, a majority still comes from fossil fuels.
The fossil fuels used to generate electricity are mainly coal and natural gas. Electricity generation from coal has been declining, from 54% in 1990 to 31% in 2017. In return, electricity generation from natural gas rose from 11% in 1990 to 31% in 2017.
Even with the decline in electricity generation from coal, the electric sector still used 93% of all coal consumed for energy in 2017.