Methane gas is a colorless and odorless gas found naturally occurring the planet over. It is the main constituent of natural gas, but methane also occurs naturally from different biological processes of animals, insects and organisms. Methane is produced both on land and in the ocean, but most of the naturally produced methane comes from the wetlands. Total annual methane emissions from natural sources are estimated to be around 250 million tons. Methane is believed to contribute to global warming because its presence increases the temperature of the atmosphere.
Natural gas found in underground deposits near water tables contains about 97 percent methane gas and is the primary natural source of methane. It also exists in small quantities near coal deposits. The methane is formed by anaerobic breakdown of organic matter below the earth’s crust, where it collects in pockets over time. Natural gas is tapped for use in industry for gas boilers and turbines and for domestic heating and cooking as a fuel.
The largest producer of methane on the planet is the wetlands, responsible for about 80 percent of the world’s natural methane emissions. As the soil becomes saturated and waterlogged, the oxygen levels are very low but carbon dioxide levels are very high. This creates a perfect environment for methanogens, which are a group of microorganisms that respire carbon dioxide and produce the large quantities of methane gas in the wetlands.
Animals produce methane is two different ways. Rudimentary animals like cows, sheep and goats produce methane by a process called enteric fermentation, which occurs in their stomach as they digest organic matter. Secondly, animals create methane from their manure and from gas they belch.
Due to the incomplete combustion of organic matter during wildfires, methane is released into the atmosphere during and after a forest fire. Fires cause the release of methane from the soil after the fire is extinguished, especially in high latitudinal regions. Additionally, the increased microbial activity caused by the increased temperatures contributes to greater amounts of methane being transferred from the soil into the atmosphere.
Termites are believed to be the second largest producer of natural methane emissions on the planet. They produce methane gas as part of their digestive process, and quantities depend on the size of termite populations. Equatorial regions where there are large populations of termites produce greater volumes of methane emissions than cooler regions where there are fewer termites.
Global emissions from methane hydrates also contribute to the natural sources of methane emissions on the planet. Methane hydrates are solid deposits of cages of water molecules containing methane. They are found deep underground in polar regions and on the ocean floor. Methane gets released when there are temperature changes, fluctuations in salt concentrations and pressure changes. Extensive research is conducted to understand how ocean changes affect the stability of these hydrates.