8.5.5: Identify the main greenhouse gases and their sources.

The Greenhouse Gases

The main greenhouse gases are methane (CH4), water vapor, carbon dioxide (CO2) and nitrous oxide (N2O).

  1. Methane: Methane is a colorless, odorless, flammable gas. It is formed when plants decay and where there is very little air. It is often called swamp gas because it is abundant around water and swamps. Bacteria that breakdown organic matter in wetlands and bacteria that are found in cows, sheep, goats, buffalo, termites, and camels produce methane naturally.
  2. Water vapor: water vapor is present naturally in the air. In areas with high humidity, there is more water vapor in the air.
  3. Carbon dioxide: Carbon Dioxide (CO2) is a colorless, odorless non-flammable gas and is the most prominent Greenhouse gas in Earth's atmosphere. It is recycled through the atmosphere by the process photosynthesis, which makes human life possible. Carbon Dioxide is emitted into the air as humans exhale, burn fossil fuels for energy, and deforest the planet. Fossil fuels, such as coal, oil and natural gas, contain carbon, and when they are burned, they combine with oxygen, forming carbon dioxide.
  4. Nitrous oxide: Nitrous oxide is another colorless greenhouse gas, however, it has a sweet odor . It is primarily used as an anesthetic because it deadens pain and for this characteristic is called "laughing gas". This gas is released naturally from oceans and by bacteria in soils.
These are the 4 main greenhouse gases responsible for the greenhouse effect.

For detailed information about the trend in emissions of these gases over centuries, go HERE.


  1. UMich.edu. University of Michigan. 12 Mar. 2009 <http://www.umich.edu/~gs265/society/greenhouse.htm>.