Methanogens and Methanotrophic Bacteria.

When analyzing the methane cycle, microbiologists focus largely on methane-producing microorganisms, specifically methanogens.  Methanogens can be found at various levels of soil, thriving at depths near the top layer of the soil and several kilometers beneath the surface.  The methanogens that exist at greater depths in the soil function in the production of methane that can be used by methanotrophic bacteria in the higher oxic soil layers.  The high efficiency of methanogens proves to be problematic for methanotrophs, as the amounts of methane are too large and are produced too fast to be completely “used up”.  Consequently, the excess methane unused by methanotrophs is released directly into the atmosphere, further enhancing the effects of global warming.  

             In opposition to methanogens, methanotrophic bacteria, a separate type of soil microorganism, function in the reduction of methane emissions.  Methanotrophic bacteria are able to use the methane produced by methanogens to carry out oxidation reactions in the presence of oxygen.  The consequence of methane regulation by methanotrophic bacteria includes a higher amount of carbon dioxide released into the atmosphere, worsening the amounts of greenhouse gases in the atmosphere and assisting in global warming.

The Methane Cycle.

            Atmospheric methane (CH₄) is a potent greenhouse gas, which functions in the regulation and variability of hydroxyl groups (-OH^-) and water vapor in the Earth’s atmosphere and plays a predominant role in global warming.  Through time, the release of methane into the atmosphere has increased significantly due to microbes and human activities involving industry, agriculture, and waste management activities.  The increase in methane combined with its higher effectiveness in trapping heat radiated from Earth have had dramatic effects in regards to global warming, contributing to an estimated 1.3° C higher globally-averaged surface temperature.

The diagram below includes a detailed illustration of the methane cycle.

It is important to note the wide variety of sources that are responsible for the release of methane into the atmosphere.  

The Carbon Cycle and Microbes.

Here I have outlined the steps of the carbon cycle from the above diagram:

1.       Carbon-based fossil fuels, coal, oil, and gas are formed.  Fossil fuels, coal, oil, and gas are acquired from the ground.
2.       Carbon is released into the atmosphere from the burning of fossil fuels, the respiration of decomposers, and the respiration of living organisms.
3.       Photosynthetic microbes and green plants absorb carbon dioxide during photosynthesis to produce glucose.  Oxygen gas is released as a byproduct.
4.       Decay of dead organisms and waste products transport carbon back into the ground.  Overtime, the decomposed remains of said organisms under the right conditions are transformed into fossil fuels such as coal and gas that can be burned and released back into the atmosphere.

In discussing the carbon cycle, scientists have begun to study more in depth the role of microbial decomposers and their contribution to global warming.  Microbial decomposers natural to the carbon cycle include various soil microorganisms that function in the decomposition of carbon from plants and other photosynthetic organisms and release of carbon dioxide into the atmosphere.  This process, also known as soil respiration, is thought to release significantly higher amounts of carbon dioxide on a yearly basis than are produced from human activities, accounting for about 25% of naturally emitted carbon dioxide.  When exposed to higher temperatures, it is predicted that soil microorganism will release larger amounts of carbon dioxide into the atmosphere, further enhancing the effects of global warming.   

The Greenhouse Gas Effect.

The increasing prevalence of greenhouse gases in the atmosphere due to human activities and microbes has intensified the absorption of thermal radiation, exclusively known as the greenhouse gas effect.  In other words, the higher levels of carbon dioxide, methane, nitrous oxide, water vapor, ozone, hydrofluorocarbons (HFCs), perfluorinated chemicals (PFCs), and sulfur hexafluoride (SF₆) in the atmosphere are reradiating solar energy to the lower atmosphere and surface of Earth, entrapping an elevated quantity of heat.  The retention of heat is thought to be the cause of rising atmospheric and ocean temperatures, which have led to concerns of global warming.  Below I have included a detailed illustration of the greenhouse gas effect to enhance understanding of the greenhouse effect.

Also, indicated below is the percentage contribution to the greenhouse effect of the more significant greenhouse gases:

• Water vapor, 36-70%
• Carbon dioxide, 9-26%
• Methane, 4-9%
• Ozone, 3-7%