Home

About Transportation and Climate Change

Emissions Inventories

Global | National | Transportation

Transportation Emissions

CO₂ from fossil fuel combustion is responsible for almost all GHG emissions from mobile sources, which include both transportation sources and nontransportation equipment such as agricultural and construction equipment. As shown in the following table, fossil fuel CO₂ accounts for 95% of mobile source GHG emissions:

U.S. Greenhouse Gas Emissions from Mobile Sources (Tg CO₂ Eq.)

* Does not include international bunker fuels.

CH4 and N2O emissions also result from fuel combustion. HFC emissions are associated with motor vehicle air conditioners.

CO2 emissions are calculated based on the carbon content and total domestic consumption of different transportation fuels (e.g., gasoline, diesel fuel, aviation gasoline, jet fuel, residual fuel oil). Subsequent calculations are performed to estimate the share of emissions attributable to different vehicle types. Results are summarized in the following table, which aggregates emissions of each of the above gases.

U.S. Greenhouse Gas Emissions from Mobile Sources, by Vehicle Type

* Does not include international bunker fuels.

As one can calculate from this table, transportation sector emissions have grown at an average rate of about 2.0 percent annually since 1990. The sector's emissions have grown considerably faster than those of other sectors, which averaged about 0.8 percent annually during the same period. Emissions from cars have grown slower than those from other highway vehicles and locomotives, and emissions from aircraft (domestic flights) have grown relatively slowly.

Data Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2004, U.S. Environmental Protection Agency, 2006.