In 2017, total gross U.S. greenhouse gas emissions were 6,472.3 MMT (million metric tons) CO₂ equivalent, a decrease of 0.3% from 2016, according to the US Environmental Protection Agency’s (EPA’s) latest Greenhouse Gas Inventory.

The decrease in total greenhouse gas emissions between 2016 and 2017 was driven in part by a decrease in CO₂ emissions from fossil fuel combustion. The decrease in CO₂ emissions from fossil fuel combustion was a result of multiple factors, including a continued shift from coal to natural gas, increased use of renewables in the electric power sector, and milder weather that contributed to less overall electricity use.

Relative to the 1990 baseline, gross emissions in 2017 were higher by 1.6%, down from a high of 15.7% above 1990 levels in 2007. Overall, net emissions in 2017 were 12.7% below 2005 levels.

Transportation. When electricity-related emissions are distributed to economic end-use sectors, transportation activities accounted for 36.5% of U.S. CO₂ emissions from fossil fuel combustion in 2017. The largest sources of transportation CO₂ emissions in 2017 were passenger cars (41.4%); medium- and heavy- 5 duty trucks (23.1%); light-duty trucks, which include sport utility vehicles, pickup trucks, and minivans (17.1%); commercial aircraft (6.7%); other aircraft (3.1%); rail (2.3%); pipelines (2.3%); and ships and boats (2.2%).

From 1990 to 2017, transportation emissions from fossil fuel combustion rose by 19% due, in large part, to increased demand for travel. The number of vehicle miles traveled (VMT) by light-duty motor vehicles (passenger cars and light-duty trucks) increased 46% from 1990 to 2017, as a result of a confluence of factors including population growth, economic growth, urban sprawl, and periods of low fuel prices.

From 2016 to 2017, CO₂ emissions from the transportation end-use sector increased by 0.84%. The small increase in emissions is attributed to both a decrease in on-road fuel use and an increase in non-road fuel use, particularly jet fuel consumption.

Almost all of the energy consumed for transportation was supplied by petroleum-based products, with more than half being related to gasoline consumption in automobiles and other highway vehicles. Other fuel uses, especially diesel fuel for freight trucks and jet fuel for aircraft, accounted for the remainder.