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What are greenhouse gases?
Of these, carbon dioxide (CO2) is the primary greenhouse gas pollutant, accounting for nearly three-quarters of global greenhouse gas emissions and 84% of U.S. greenhouse gas emissions. The EPA maintains that carbon pollution leads to long-lasting changes in our climate, such as:
According to the US EPA, the primary sources of greenhouse gas emissions in the United States are:
Electricity production (32% of 2012 greenhouse gas emissions) - Electricity production generates the largest share of greenhouse gas emissions. Over 70% of our electricity comes from burning fossil fuels, mostly coal and natural gas.
Transportation (28% of 2012 greenhouse gas emissions) - Greenhouse gas emissions from transportation primarily come 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.
Industry (20% of 2012 greenhouse gas emissions) - Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials.
Commercial and Residential (10% of 2012 greenhouse gas emissions) - Greenhouse gas emissions from businesses and homes arise primarily from fossil fuels burned for heat, the use of certain products that contain greenhouse gases, and the handling of waste.
Agriculture (10% of 2012 greenhouse gas emissions) - Greenhouse gas emissions from agriculture come from livestock such as cows (did you know they burp and fart large quantities of methane?), agricultural soils, and rice production.
Land Use and Forestry (offset of 15% of 2012 greenhouse gas emissions) - Land areas can act as a sink (absorbing CO2 from the atmosphere) or a source of greenhouse gas emissions. In the United States, since 1990, managed forests and other lands have absorbed more CO2 from the atmosphere than they emit.
Since 1990, U.S. greenhouse gas emissions have increased by about 5%. From year to year, emissions can rise and fall due to changes in the economy (when there is a recession, people buy and use less), the price of fuel (when oil and gas are expensive, people cut out vacations and reduce driving), and other factors. In 2012, U.S. greenhouse gas emissions decreased compared to 2011 levels. The EPA believes this decrease was primarily due to a decrease in the carbon intensity of fuels consumed to generate electricity due to a decrease in coal consumption, with increased natural gas consumption and a significant increase in hydropower used. Natural gas burns much more cleanly than other fossil fuels and of course, hydroelectric power plants produce only negligible amounts of greenhouse gases.
Additionally, relatively mild winter conditions, especially in the South Atlantic Region of the United States where electricity is used in heatingmany homes, resulted in an overall decrease in electricity demand in most sectors.
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