Most municipal solid waste (MSW) in the United States is deposited in landfills, where bacteria decompose the organic material.

A product of the bacterial decomposition is landfill gas, which is composed of CH4 and carbon dioxide (CO2) in approximately equal concentrations, as well as smaller amounts of non­methane volatile organic compounds (NMVOC), nitrogen oxides (NOX), and carbon monoxide (CO).

If not collected and combusted, over time, this landfill gas is released to the atmosphere. In the United States, landfills are one of the largest sources of anthropogenic emissions of CH4, accounting for 23 percent of total CH emissions. — United States EPA

Your carbon footprint is the sum of all emissions of CO2 (carbon dioxide), which were induced by your activities in a given time frame. Usually a carbon footprint is calculated for the time period of a year. — TimeForChange.org

The EPA provides an online calculator for estimating personal emissions.

Check the fuel economey for your car at FuelEconomy.gov.

CO2 emissions - On average, 16 million tons of carbon dioxide are emitted into the atmosphere every 24 hours by human activities. — BP

Average CO2 emissions by fuels - Natural gas produces about half the CO2 per unit of energy compared with coal. Natural Gas (0,19 kg CO2 / kWh), Coal (0,30kg CO2 / kWh). — BP

Methane - When vegetable matter decomposes in the absence of oxygen biogas is produced. Biogas is about 70% methane and 30% carbon dioxide (natural gas is almost 100% methane). — BP

Lighting - One normal 100 watt light bulb creates a party balloon full of CO2 every half hour that it is on. — BP

Efficient Appliances - If everyone in the UK upgraded their fridges and freezers to Energy Saving Recommended ones, energy wastage would be cut by two thirds, saving nearly £500 million and the equivalent CO2 emissions of 350,000 homes. — BP

A Methane powered engine produces electricty at DADs in Colorado An oil refinery An example of methane production in a landfil