Transportation is not solely responsible for the mess of greenhouse gas (GHG) emissions in the air, but our cars and trucks (and ships, trains, and planes) were the second-biggest factor in GHG in the US in 2011. The good news is that overall emissions are on the decline, dropping 1.6 percent in 2011 (the latest figures available) compared to 2010. Overall GHG emissions in 2011 were the equivalent of 6,702 million metric tons of carbon dioxide in the air. It's been over 6,000 every year since at least 1990.

The numbers come from the 18th Annual US Greenhouse Gas Inventory, which shows that the annual emissions in 2011 were 6.9 percent below 2005 levels. GHG are made up of carbon dioxide (84 percent), methane (9), nitrous oxide (5) and flourinated gases (2).

According to the US Environmental Protection Agency (EPA), electricity was the number one contributor in 2011, responsible for 33 percent of GHG, followed by transportation at 28 percent. The rest of the pie chart is made up of industry (20 percent), commercial and residential (11) and agriculture (8). Within the transportation category, the EPA says GHG come primarily "from burning fossil fuel for our cars, trucks, ships, trains, and planes. Over 90% of the fuel used for transportation is petroleum based, which includes gasoline and diesel." Which makes sense, then, that cleaner vehicles and fewer miles traveled helped reduce the impact of our vehicles on the air we breathe.
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EPA Publishes 18th Annual U.S. Greenhouse Gas Inventory

WASHINGTON – Today, the U.S. Environmental Protection Agency (EPA) released its 18th annual report of overall U.S. greenhouse gas (GHG) emissions showing a 1.6 percent decrease in 2011 from the previous year. Recent trends can be attributed to multiple factors including reduced emissions from electricity generation, improvements in fuel efficiency in vehicles with reductions in miles traveled, and year-to-year changes in the prevailing weather.

Under this Administration, EPA has taken a number of common sense steps to help reduce GHG emissions. This includes increasing fuel efficiency for cars that will reduce America's dependence on oil by an estimated 12 billion barrels by 2025, and increasing energy efficiency through the Energy Star program that saved Americans $24 billion in utility bills in 2012.

GHGs are the primary driver of climate change, which can lead to hotter, longer heat waves that threaten the health of the sick, poor or elderly; increases in ground-level ozone pollution linked to asthma and other respiratory illnesses; as well as other threats to the health and welfare of Americans. GHG emissions in 2011 showed a 6.9 percent drop below 2005 levels. Total emissions of the six main greenhouse gases in 2011 were equivalent to 6,702 million metric tons of carbon dioxide. These gases include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.

The Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2011 is the latest annual report that the United States has submitted to the Secretariat of the United Nations Framework Convention on Climate Change since it was ratified by the United States in 1992. The treaty sets an overall framework for intergovernmental efforts to address the challenge posed by climate change. EPA prepares the annual report in collaboration with other federal agencies and after gathering comments from stakeholders across the country.

The inventory tracks annual GHG emissions at the national level and presents historical emissions from 1990 to 2011. The inventory also calculates carbon dioxide emissions that are removed from the atmosphere through the uptake of carbon by forests, vegetation, soils, and other natural processes (called carbon "sinks").

For a graphic illustrating total U.S. GHG emissions by year, visit
www.epa.gov/climatechange/ghgemissions/sources.html#emissions-and-trends

More on the greenhouse gas inventory report:
http://www.epa.gov/climatechange/emissions/usinventoryreport.html