|US end-use sector emissions of greenhouse gases. Click to enlarge.|
The transportation sector in the US accounts for approximately 33% of total greenhouse gas emissions from fossil-fuel combustion, and again represents the largest share of any end-use economic sector, according to a just-published draft of the US Greenhouse Gas Inventory by the Environmental Protection Agency (EPA). (End-use sectors are transportation, industrial, commercial and residential.)
In 2005, total US greenhouse gas emissions were 7,262.3 teragrams of carbon dioxide equivalents. Overall, total US emissions have risen by 16.3% from 1990 to 2005, while the US gross domestic product has increased by 55% over the same period.
According to EPA’s allocations, transportation accounted for 1,899.5 Tg CO2 (in CO2 equivalents) in 2005 out of a total 5,752.8 Tg CO2 generated by fossil fuel combustion. Between 1990 and 2005, transportation CO2 emissions increased by 432.5 Tg CO2, representing approximately 41% of the growth in energy-related CO2 emissions from all sectors.
Within the transportation sector, CO2 emissions increased by 29% from 1990 to 2005, representing an average annual increase of 1.8%. Between 2004 and 2005 transportation CO2 emissions increased by 1.6%. Almost all of the energy consumed in the transportation sector was petroleum-based, including motor gasoline, diesel fuel, jet fuel, and residual oil.
Automobiles and light-duty trucks accounted for approximately 61% of transportation CO2 emissions in 2005, down slightly from 63% in 1990. From 1990 to 2005, CO2 emissions from automobiles and light-duty trucks increased roughly 25% (236.2 Tg CO2). Over this period, vehicle miles traveled (VMT) by automobile and light-duty trucks increased by 39%, outweighing a small increase in overall fleet fuel economy that resulted from the retirement of older vehicles.
Carbon dioxide emissions from freight trucks increased by 69% (157.7 Tg) from 1990 to 2005, representing the largest emissions rate increase of any major transportation mode. Truck VMT increased by 51%.
While CO2 emissions from commercial aircraft grew by approximately 16% (21.8 Tg CO2) from 1990 to 2005, passenger miles traveled (PMT) increased by 69% over the same period, reflecting improvements in the fuel efficiency of planes and an increasing percentage of occupied seats per plane.
The EPA has made the draft of the Inventory of US Greenhouse Gas Emissions and Sinks 1990 - 2005 available for public comment.