In the U.S., our energy-related activities account for three-quarters of our human-generated greenhouse gas emissions, mostly in the form of carbon dioxide emissions from burning fossil fuels. More than half the energy-related emissions come from large stationary sources such as power plants, while about a third comes from transportation. Industrial processes (such as the production of cement, steel, and aluminum), agriculture, forestry, other land use, and waste management are also important sources of greenhouse gas emissions in the United States.
For a better understanding of where greenhouse gas emissions come from, governments at the federal, state and local levels prepare emissions inventories, which track emissions from various parts of the economy such as transportation, electricity production, industry, agriculture, forestry, and other sectors. EPA publishes the official national inventory of US greenhouse gas emissions, and the latest greenhouse gas inventory shows that in 2005 the U.S. emitted over 7.2 billon metric tons of greenhouse gases (a million metric tons of CO2 equivalents (MMTCO2e) is roughly equal to the annual GHG emissions of an average U.S. power plant.) Visit the Emissions section of this site to learn more, or review the answers to some frequent emissions questions.
Carbon dioxide (CO2) is emitted in a number of ways. It is emitted naturally through the carbon cycle and through human activities like the burning of fossil fuels.
Natural sources of CO2 occur within the carbon cycle where billions of tons of atmospheric CO2 are removed from the atmosphere by oceans and growing plants, also known as ‘sinks,’ and are emitted back into the atmosphere annually through natural processes also known as ‘sources.’ When in balance, the total carbon dioxide emissions and removals from the entire carbon cycle are roughly equal.
Since the Industrial Revolution in the 1700’s, human activities, such as the burning of oil, coal and gas, and deforestation, have increased CO2 concentrations in the atmosphere. In 2005, global atmospheric concentrations of CO2 were 35% higher than they were before the Industrial Revolution.
In the home or on the road, daily activities cause emissions of greenhouse gases. Individuals can produce greenhouse gas emissions directly by burning oil or gas for home heating or indirectly by using electricity generated from fossil fuel burning.
Within the United States, per person emissions can vary depending on a person’s location, habits and personal choices. For example, the types of fuel used to generate the electricity a person uses can lead to different levels of emissions. A power plant run on coal emits more greenhouse gases per unit of electricity than a power plant that uses natural gas. How much you drive and your vehicle's fuel efficiency, as well as time spent idling in traffic, also affect the level of emissions. In addition, the amount of recycling done by a person in his or her home can affect emissions by reducing the amount of methane-generating waste sent to landfills.
Through actions at home, at work, and on the road, individuals can affect their greenhouse gas emissions levels. The first step in reducing your greenhouse gas emissions is to identify how much your household emits. If you have old copies of energy bills, EPA’s personal greenhouse gas emissions calculator can help estimate your household’s annual emissions.