Methane is a colorless, odorless gas with the molecular formula CH4. It is the main chemical component of natural gas (accounting for 70-90 percent of such gas). Natural gas makes up up to 20 percent of the U.S. energy supply. Methane was discovered by the Italian scientist Alessandro Volta, who collected it from marsh sediments and demonstrated that it was flammable. He called it “combustible air.”
Natural sources of methane include wetlands, lake sediments, natural gas fields, termites, oceans, permafrost, and methane hydrates. Wetlands are responsible for up to 76 percent of global natural methane emissions. Surprisingly, according to EPA data, termites contribute about 11 percent of global natural methane emissions. In most of these processes, methane is produced by microorganisms called archaea as the integral part of their metabolism. Such microbes are called methanogens, and the route of methane generation is called methanogenesis.
Methane as a Greenhouse Gas
As with all greenhouse gases (GHGs), methane in the atmosphere acts similarly to glass in a greenhouse. It allows light energy from the Sun to reach Earth’s surface, but it traps heat energy radiated back from the surface in the form of infrared radiation. Since the beginning of the Industrial Revolution in the mid-eighteenth century, methane concentrations have more than doubled in the atmosphere, causing nearly one-quarter of the planet’s anthropogenic global warming. Continuous release of methane into the atmosphere causes rapid warming, because methane’s contribution to the greenhouse effect is much more powerful than that of carbon dioxide (CO2).
Global warming itself may trigger the release of methane trapped in tundra permafrost or ocean deposits, thereby accelerating climate change in a positive feedback loop. The release of large volumes of methane from such geological formations into the atmosphere has been suggested as a possible cause for global warming events in the past. Methane oxidizes to CO2 and therefore remains in the atmosphere for a shorter time-period of nine to fifteen years, compared to CO2, which may remain in the atmosphere for one hundred years.