The US Environmental Protection Agency (EPA) has released the 16th annual US greenhouse gas (GHG) inventory. The final report shows overall emissions during 2009 decreased by 6.1% from the previous year. This downward trend was attributed to a decrease in fuel and electricity consumption across all US economic sectors.
Total emissions of the six main greenhouse gases in 2009 were equivalent to 6,633 million metric tons of carbon dioxide. These gases include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride. The report indicates that overall emissions have grown by more than 7.3% from 1990 to 2009. Emissions in 2009 represent the lowest total US annual GHG emissions since 1995. These numbers reflect the most up to date data at the time of publication.
The transportation end-use sector accounted for 1,745.5 Tg CO2 Eq. in 2009, which represented 33% 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 123.1 Tg CO2 in 2009; these emissions are recorded as international bunkers and are not included in US totals according to UNFCCC reporting protocols. Among domestic transportation sources, light duty vehicles (including passenger cars and light-duty trucks) represented 64% of CO2 emissions, medium- and heavy-duty trucks 20%, commercial aircraft 6%, and other sources 9%.
Light-duty truck CO2 emissions increased by 60% (193.4 Tg) from 1990 to 2009, representing the largest percentage increase of any transportation mode. General aviation aircraft CO2 emissions also increased by nearly 60% (5.7 Tg) from 1990 to 2009. CO2 from the domestic operation of commercial aircraft decreased by 18% (24.0 Tg) from 1990 to 2009. Across all categories of aviation, CO2 emissions decreased by 21.6% (38.7 Tg) between 1990 and 2009. This includes a 59% (20.3 Tg) decrease in emissions from domestic military operations.
From 1990 to 2009, transportation emissions rose by 17% due, in large part, to increased demand for travel and the stagnation of fuel efficiency across the US vehicle fleet. The number of vehicle miles traveled by light-duty motor vehicles (passenger cars and light-duty trucks) increased 39% from 1990 to 2009, as a result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices over much of this period.
From 2008 to 2009, CO2 emissions from the transportation end-use sector declined 4%. The decrease in emissions can largely be attributed to decreased economic activity in 2009 and an associated decline in the demand for transportation. Modes such as medium- and heavy-duty trucks were significantly impacted by the decline in freight transport. Similarly, increased jet fuel prices were a factor in the 19% decrease in commercial aircraft emissions since 2007.
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 primary driver of transportation-related emissions was CO2 from fossil fuel combustion, which increased by 16% from 1990 to 2009. This rise in CO2 emissions, combined with an increase in HFCs from close to zero emissions in 1990 to 60.2 Tg CO2 Eq. in 2009, led to an increase in overall emissions from transportation activities of 17%.
The Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2009 tracks annual greenhouse gas emissions at the national level and presents historical emissions from 1990 to 2009. 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 inventory, prepared in collaboration with federal agencies, is the latest submitted by the United States to the Secretariat of the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC sets an overall global framework for nations to address climate change. The final report takes into consideration comments received from stakeholders across the country.