Explain like I’m Five: Methane and the Greenhouse Effect

By PSU EcoMerge Capstone - 5:37 PM


The greenhouse effect is a naturally occurring phenomenon necessary for the Earth to maintain a habitable temperature. This occurs when sunlight passes through the atmosphere and heats the Earth’s surface before reflecting back (in the form of infrared light) toward the atmosphere. Certain gases in the atmosphere capture different levels of this energy, which allows some to pass through, while some is maintained and disbursed through the atmosphere to maintain temperatures. Through human intervention however, the levels of these gases have increased, effectively ‘ thickening’ the barrier between our atmosphere and space and capturing more and more heat. More energy is trapped by the increase of gases, which increases the heat retained, and even causes deposits of greenhouse gases, trapped beneath the ocean and in the polar ice caps for example, to be released and perpetuate the problem. This can eventually lead to a “runaway” greenhouse effect that (given a few billion years) could potentially create an atmosphere similar to Venus. The Earth would be uninhabitable long before that however.
So what are these greenhouse gases? There are a handful of gases bouncing around the atmosphere but these are the big three are water vapor, carbon dioxide and methane. The number one perpetrator is actually water vapor naturally occurring in the atmosphere. Just plain ol’ H2O , however, comparative to the other major greenhouse gas players, cannot be directly affected by human behaviors— water vapor levels are directly affected by air temperatures and evaporation caused by surface temperatures. It follows that water vapor levels can only stabilize if overall temperatures do— which means looking to the other perpetrators for means of reduction. Carbon dioxide, or CO2, is probably the best known global contributor. Carbon dioxide comes from many natural sources such as volcanoes, organic decay, respiration as well as human productions through industrial processes and fossil fuel dependence. Furthermore, decreases in plant life through deforestation and ocean die-off (partially through rising temperatures!) have cut the natural rate of CO2 removal that occurs through photosynthesis. Then there is methane, CH4, which up until recently has been the underestimated big hitter. Methane has generally been shifted to second tier because it is comparatively less concentrated in the atmosphere than CO2. Methane however is both more “potent” while quicker to to decay. This means two things, when in the atmosphere it has a greater effect than CO2 in per mass units, but when adding in its higher decay rate it, then has the potential to cause twice as much of a positive effect when actively decreased. Methane is a tricky beast however, it occurs naturally from bacterial decay of organic matter (an effect similarly perpetuated by landfills), from wetlands, volcanoes and natural seepage from deposits in the ocean and ice caps. These regions where methane deposits (also known as natural gas and a prevalent energy supply) increase dispersal as things heat up. Under the ocean pressure changes have created greater releases of CH4 and shrinking polar ice caps are exposing similar deposits for release. This then becomes a self-perpetuating problem. Unlike CO2, where plant life helps the decay rate, CH4 naturally decays primarily through natural decay in the atmosphere when in contact with water vapor. This becomes complicated when CH4 levels increase. There is however another major human driven source for methane: agriculture, of which cow farts (yes, seriously), other livestock ‘emissions’, and rice production reign supreme. Where the US, and to a lesser extent other industrialized nations, have moved farther and farther from plant based diets, while proportionally increasing dramatically in population, methane levels have risen accordingly. Here is a handy video further explaining Methane’s role as a greenhouse gas and how it interacts with the better known antagonist Carbon Dioxide.




Sources:
http://msue.anr.msu.edu/uploads/234/62936/Greenhouse_Gas_Basics.pdf
http://www3.epa.gov/climatechange/ghgemissions/gases/ch4.html

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