DOT Center for Climate Change | About Transportation and Climate Change

Under Article 4 of the United Nations Framework Convention on Climate Change (UNFCCC), the U.S. and other signatories have committed to the development, periodic update, and publication of national inventories of sources and sinks (e.g., forests) of greenhouse gas emissions resulting from human activities, consistent with calculation methodologies agreed upon by the Conference of Parties to the UNFCCC.

The U.S. Environmental Protection Agency (EPA) prepares the Nation's inventory of greenhouse gas emissions and sinks. To ensure that the U.S. emissions inventory is comparable to those of other UNFCCC signatory countries, EPA uses methodologies consistent with those recommended by the Intergovernmental Panel on Climate Change (IPCC). These guidelines utilize the major source and sink categories summarized below:

IPCC Greenhouse Gas Source/Sink Categories*

Sector	Description
Energy	Total GHG emissions from stationary and mobile fuel combustion and fugitive emissions
Industrial Processes	By-product or fugitive emissions from industrial processes
Solvent and Other Product Use	Primarily NMVOC* emissions from the use of solvents and other products with volatile compounds
Agriculture	All anthropogenic emissions from agriculture, except for fuel combustion and sewage emissions
Land-Use Change and Forestry	Total emissions and removals from forest and land-use change activities
Waste	Total emissions from waste management
Other	Any other anthropogenic source or sink

*Nonmethane volatile organic compounds.

Under these guidelines, the majority of transportation-related emissions, which result from the combustion of transportation fuels, are reported as a subset of the energy sector.

As shown below, CO2 accounts for more than 80% of U.S. GHG emissions. Nearly all of this CO2 is from fossil fuel combustion. Transportation-related emissions are shown in shaded rows and marked with a ¤.

Aggregate U.S. Greenhouse Gas Emissions (Tg CO2 Eq.)

CO2*

End-Use Sector	1990	1995	2000	2001	2002	2003	2004
Industrial	1528.3	1710.5	1642.8	1574.9	1542.8	1572.4	1595.0
¤Transporation	1464.4	1565.3	1770.3	1757.0	1802.2	1805.4	1860.2
Residential	922.8	995.0	1123.2	1123.2	1139.8	1166.6	1166.8
Commercial	753.1	808.3	961.6	983.3	973.9	978.1	983.1
Other	336.7	246.2	366.6	356.8	357.2	355.2	382.9
Total	5005.3	5325.3	5864.5	5795.2	5815.9	5877.7	5988.0

CH4 (Methane)*

Source	1990	1995	2000	2001	2002	2003	2004
¤Mobile Sources	4.7	4.3	3.5	3.3	3.2	3.0	2.9
Landfills	172.3	163.2	139.0	136.2	139.8	142.4	140.9
Enteric Fermentation	117.9	123.0	115.6	114.6	114.7	115.1	112.6
Natural Gas Systems	126.7	128.1	126.7	125.6	125.4	124.7	118.8
Coal Mining	81.9	65.8	56.3	55.5	52.5	54.8	56.3
Manure Management	31.2	36.1	38.0	38.9	39.3	39.2	39.4
Other	88.1	92.8	91.3	89.5	88.1	88.1	88.7
Total	618.1	608.9	566.9	560.3	559.8	564.4	556.7

N2O*

Source	1990	1995	2000	2001	2002	2003	2004
¤Mobile Sources	43.5	53.4	53.1	50.0	47.5	44.8	42.8
Agricultural Soil Management	266.1	308.1	278.2	282.9	277.8	259.2	261.5
Other	85.3	92.7	84.9	79.9	82.1	82.1	82.4
Total	394.9	454.2	416.2	412.8	407.4	386.1	386.7

HFC's, PFC's and SF6

Source	1990	1995	2000	2001	2002	2003	2004
¤Mobile Air Conditioners	+	8.9	32.6	36.1	38.9	41.2	45.0
Other	90.8	85.9	102.1	88.8	93.8	89.8	98.0
Total	90.8	94.8	134.7	124.9	132.7	131.0	143.0

+ Does not exceed 0.05 Tg CO2 Eq.

Total Emissions

	1990	1995	2000	2001	2002	2003	2004
Total Emissions	6109.0	6484.7	6982.3	6893.1	6915.8	6959.1	7074.4
CO2 Sinks	(910.4)	(948.0)	(759.5)	(768.0)	(768.6)	(774.8)	(780.1)
Net Emission	5198.6	5536.7	6222.8	6125.1	6147.2	6184.3	6294.3

Several aspects of these data are notable from a transportation perspective. First, CO2 emissions from transportation fuel use have grown almost every year from 1990 through 2004, and the overall increase in transportation CO2 emissions is larger than for any of the other domestic sectors. Second, although mobile source N2O emissions grew in the early 1990s, that trend has since reversed course and these emissions have declined slowly. Third, while HFC emissions from mobile air conditioners were non-existent in 1990, they have grown rapidly during the decade. Finally, transportation does not contribute significantly to CH4 emissions.

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