This decrease was largely driven by a decrease in emissions from fossil fuel combustion, which was a result of multiple factors including a continued shift from coal to natural gas and increased use of renewables in the electric power sector, and milder weather that contributed to less overall electricity use.
In 2017, US greenhouse gas emissions totaled 6,456.7 million metric tons of carbon dioxide equivalents, or 5,742.6 million metric tons of carbon dioxide equivalents after accounting for sequestration from the land sector.
Since 2005, national greenhouse gas emissions have fallen by 13%, and power sector emissions have fallen by 27.6%.
The transportation sector now generates the largest share of greenhouse gas emissions in the US—28.9% of 2017 greenhouse gas emissions. More than 90% of the fuel used for transportation is petroleum-based, which includes primarily gasoline and diesel.
From 2016 to 2017, CO2 emissions from the transportation end-use sector increased by 1.21%. The small increase in emissions is attributed to an increase in diesel fuel consumption by medium- and heavy-duty trucks and jet fuel consumption by commercial aircraft.
In terms of the overall trend, from 1990 to 2017, total transportation emissions have increased 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 by 45.9% 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.
Between 1990 and 2004, average fuel economy among new vehicles sold annually declined, as sales of light-duty trucks increased. Starting in 2005, average new vehicle fuel economy began to increase while light-duty VMT grew only modestly for much of the period. Average new vehicle fuel economy has improved almost every year since 2005, and the truck share is about 45% of new vehicles in model year 2016. . . .
