Where Greenhouse Gases Come From
In the United States, greenhouse gas emissions come primarily from the burning of fossil fuels in energy use.
Carbon Dioxide is the main greenhouse gas. In 2008, 81% of human-caused greenhouse gas emissions were carbon dioxide emissions, resulting from the use of petroleum, coal, and natural gas.
Methane and Other Gases
Another greenhouse gas, methane, comes from landfills, coal mines, oil and natural gas operations, and agriculture; it represented about 11% of total emissions. Nitrous oxide (4% of total emissions) is emitted through the use of nitrogen fertilizers, from burning fossil fuels, and from certain industrial and waste management processes.
The Energy Connection
Fossil fuels are made up of hydrogen and carbon. When fossil fuels are burned, the carbon combines with oxygen to create carbon dioxide. The amount of carbon dioxide produced depends on the carbon content of the fuel; for example, for each unit of energy produced, natural gas emits about half and petroleum fuels about three-quarters of the carbon dioxide produced by coal.
America is a Nation on the move. About 27% of the energy we use goes to transporting people and goods from one place to another.
Cars, vans, and buses are commonly used to carry people. Trucks, airplanes, and trains can be used to carry people and freight. Barges and pipelines only carry freight. In 2008, there were 250 million vehicles (cars, buses, and trucks) in the United States — more than three motor vehicles for every four people.
Automobiles, motorcycles, trucks, and buses traveled just over 3.0 trillion miles in the United States in 2008. That’s almost one-twelfth the distance to the nearest star beyond the solar system. It’s like driving to the sun and back 13,440 times.
Energy Use By Type of Vehicle
Automobiles are the most common mode of transportation in the United States. Personal vehicles (like cars and light trucks) consume 60% of the total energy used for transportation, while commercial vehicles (like large trucks and construction vehicles), mass transit (like airplanes, trains, and buses), and pipelines account for the rest.
Carbon Dioxide Emissions Are Expected to Increase
World carbon dioxide emissions are expected to increase by 1.3% annually between 2007 and 2035. Much of the increase in these emissions is expected to occur in the developing world where emerging economies, including China and India, fuel economic development with fossil energy.
The United States produced about 23% of global carbon dioxide emissions from burning fossil fuels in 2007, and 19% in 2008, the most recent year for which global data are available. The United States has the world's largest economy and meets 84% of its energy needs by burning fossil fuels.