CO2 emissions from the US transport sector, 1990-2008. Data: EPA. Click to enlarge.

The draft report of the US Environmental Protection Agency (EPA)’s annual Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2008 shows that in 2008, overall greenhouse gas (GHGs) emissions decreased by 2.9% (206.1 Tg CO₂ Eq). This report attributes the downward trend primarily to the decrease in demand for transportation fuels associated with the record high costs of these fuels that occurred in 2008.

CO₂ emissions from the transportation sector dropped 5.7% to 1,785.3 Tg CO₂ in 2008 from 1,893.8 Tg CO₂ the year before—the largest annual change in either absolute or percentage terms recorded between 1990 and 2008.

Additionally, electricity demand declined in 2008 in part due to a significant increase in the cost of fuels used to generate electricity. Total emissions from GHGs were about 6,946 million metric tons of carbon dioxide (CO₂) equivalent. Overall, emissions have grown by 13.6% from 1990 to 2008. The report is open for public comment for 30 days after the Federal Register notice is published.

Transportation. The transportation end-use sector accounted for 1,818.1 Tg CO2 Eq. in 2008—32% of CO₂ emissions, 24% of CH₄ emissions, and 65% of N₂O emissions from fossil fuel combustion, respectively. Fuel purchased in the US for international aircraft and marine travel accounted for an additional 135.2 Tg CO₂ in 2008; these emissions are recorded as international bunkers and are not included in US totals according to UNFCCC reporting protocols.

Light duty vehicles represented 62% of CO₂ emissions within the sector, medium- and heavy-duty trucks 22%, commercial aircraft 7%, and other sources 9%.

From 1990 to 2008, transportation emissions have risen by 22% due, in large part, to increased demand for travel and the stagnation of fuel efficiency across the US vehicle fleet. Vehicle miles traveled (VMT) by light-duty motor vehicles increased 37% from 1990 to 2008 as a result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices over much of this period. Similar social and economic trends led to a significant increase in air travel and freight
30 transportation by both air and road modes during the time series.

EPA largely attributed the decrease in transportation sector emissions in 2008 to the decline in economic activity and the increased price of transportation fuels. 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.

The inventory tracks annual greenhouse gas emissions from 1990 to 2008 at the national level. The gases covered by this inventory include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride. The inventory also calculates carbon dioxide emissions that are removed from the atmosphere by “sinks,” e.g., through the uptake of carbon by forests, vegetation, and soils.

This annual report is prepared by EPA in collaboration with experts from other federal agencies. After responding to public comments, the US government will submit the final inventory report to the Secretariat of the United Nations Framework Convention on Climate Change (UNFCCC). The report will fulfill the annual requirement of the UNFCCC international treaty, ratified by the United States in 1992, which sets an overall framework for intergovernmental efforts to tackle the challenge posed by climate change.

Resources

• 2010 Draft US Greenhouse Gas Inventory Report

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