A renewable energy system generating around 30,000 kWh of green electricity per year, will offset around 17 tons of CO2 emissions from existing fossil fuel energy generation. This is sufficient to bring the carbon footprint of the average four person household back to zero (household energy use + car + air travel).

In the United States, greenhouse gas emissions come primarily from the burning of fossil fuels in energy use. 

Carbon Dioxide

Energy-related carbon dioxide emissions, resulting from the combustion of petroleum, coal, and natural gas, represented 81% of total U.S. human-caused (anthropogenic) greenhouse gas emissions in 2008.

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. Several human-made gases, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), that are released as byproducts of industrial processes and through leakage, represented about 3% of total emissions.

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.

Most of Our Carbon Dioxide Emissions Come from Coal and Petroleum Use

Seventy-eight percent of U.S. energy-related carbon dioxide emissions came from the use of coal and petroleum fuels in 2008, and about 21% came from natural gas. Although the industrial sector is the largest consumer of energy (including direct fuel use and purchased electricity), the transportation sector emits more carbon dioxide because of its near complete dependence on petroleum fuels.

The residential and commercial sectors have lower emission levels than transportation and industry. Most of their emissions come from fossil energy combustion to produce electricity.

Coal Is the Dominant Emissions Source Related to Electricity Generation

Electricity generation consumed 41% of U.S. primary energy in 2008 and was responsible for 41% of energy-related carbon dioxide emissions. Coal accounted for 83% of carbon emissions resulting from the generation of electric power.