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What are the Top Greenhouse Gases and Where Do They Come From?
While Carbon Dioxide is probably the most widely discussed greenhouse gas, there are several others in the atmosphere. Below are the 5 most prevalent greenhouse gases in our atmosphere and where these gases originate from.
Water vapor is the most prominent greenhouse gas making up roughly 36-72% of all the greenhouse gases in the air and is roughly 4% of the atmosphere overall. The presence of water is the result of the hydrologic/water cycle. As water evaporates and condenses and then rains/snows; the levels in the atmosphere changes. While it is the largest greenhouse gas it is hard to distinguish what impact humans have on it compared to normal cycles because it fluctuates and varies so much naturally. It is speculated that as temperature rises the amount of water vapor present can rise and that will further compound heating of the planet. However, water vapor also collects and condenses forming clouds which also reflect some of the sun's rays and subsequently has a cooling effect.
Overall, it is a complex cycle that may evolve as conditions change.
Carbon Dioxide is the second most prominent greenhouse gas making up roughly 9-26% of the greenhouse gases and is roughly 0.04% of the atmosphere overall.
Human carbon dioxide production accounts for 6% of carbon dioxide production overall. The remainder is the result of natural occurrences in the Carbon cycle via respiration, decomposition, and other exchanges between the land, oceans, and the atmosphere. Volcanoes are a source of carbon dioxide as well, however, they contribute roughly 100 times less carbon dioxide than human causes. The reason why that 6% from humans is due to the impact is because the carbon cycle is not in equilibrium. The ocean and land in general absorb as much carbon dioxide as they produce and historically have on average stayed around 200 PPM. However, with the addition of human introduced carbon dioxide there is a surplus not being removed from the atmosphere as the oceans and land are not keeping up with what is being emitted with the natural causes and human causes combined. That delta ends up being an additional 2 PPM of CO2 in the atmosphere each year.
U.S Carbon Dioxide Emissions for Humans
Residential & Commercial
Other (Non-Fossil Fuel Combustion)
Methane is the third most prominent greenhouse gas making up roughly 4-9% of the gas constituents and roughly 0.0002% of the atmosphere overall. Out of the Methane produced/released about 60% globally comes from human activities.
In the United States:
-39% of the human produced emissions come from the petroleum industry through the various phases from extraction, processing, and eventual distribution of natural gas, coal, and other fossil fuels
-25% comes from livestock animals through their digestive cycles
-18% comes from the decomposition of landfill materials.
-9% is related to the management and uses of that manure.
For the sources of methane outside humans the largest is from wetlands via anaerobic decomposition of materials by bacteria. Termites, oceans, wildfires, and volcanoes are also sources of methane. Methane is absorbed via aerobic reactions with bacteria and reactions with water and free radicals in the atmosphere. Also, it is worth noting that the ice caps store a significant amount of methane as well. As those caps melt the methane trapped in them is released.
Do you think that there is a relationship between human introduction of greenhouse gases and the climate?
Nitrous Oxide is the fourth most prominent greenhouse gas making up roughly 0.00003% of the atmosphere overall. The majority (60%) is the result of natural Nitrogen cycles via the processes of nitrification and denitrification. The remaining 40% is produced by human activities. In the United States, Four-fifths of human sources come from agriculture, particularly when synthetic fertilizer applied or when grazing livestock defecate or urinate and Nitrous Oxide is liberated. The remaining fifth comes from the reactions from combustion of fuels and the production of nylon, nitric acid, and other industrial products.
Ozone is the fifth most prominent greenhouse gas making up roughly 3-7% of the constituents and roughly 0.00001% of the atmosphere overall. Stratospheric ozone, or the ozone layer is the result of reactions from solar radiation and oxygen gas. However, tropospheric ozone, which is ground level ozone, is largely the result for reactions between volatile organic compounds (VOC's) and nitrogen oxides with the aid of solar radiation. VOC's occur both naturally via nature through plants, animals, microbes, and fungi. They are also present in man made solvents like paints, household cleaners, and varnishes. In urban areas, automobile emissions coupled with VOC's are thought to be contributors to spikes in ground ozone levels.
Other Greenhouse Gases
While the aforementioned gases are the largest constituents, they are not the only gases introduced by humans that can play a role in the greenhouse effect. Trifluoromethane also known as Fluoroform is used for fire retarding and microchip processes is also a greenhouse gas contributor. Hexafluoroethane, another greenhouse gas, is introduced via the semiconductor industry. It is also worth noting that Hexafluoroethane does not break down readily in the atmosphere and can last 500 to 10,000 years in the air. Sulfur Hexafluoride, used in insulators, is the most potent evaluated greenhouse gas by the IPPC. Relative to carbon dioxide the warming potential is more severe by ~20,000 times. Currently, there is approximately 7 parts per trillion in the atmosphere.
Why Does Human Impact Matter?
There are 7.4 Billion people on the Earth today and we are expected to add another 800 million over the next 10 years. As we further advance in technology and close the gaps between first world and developing economies; it is worth thinking about how the changes we make affect the balance of the systems around us. With these changes come higher demands for food, manufactured goods, cars and ultimately energy.
While it may seem implausible for anything humans do to make a significant impact on this large, complicated planet; we have seen throughout history that we can alter the planet in a relatively short time span. We have created massive holes in the Ozone layer through use of CFC's; but recognized the our impact and consequences and were able to alter our practices to help reverse the changes. From those changes, the ozone layer has receded at much as 30% since peaks in 2000. Overall, understanding to what extent we impose changes on the Earth cycles is one of the first steps in determining the significance of our actions and ultimately where the constraints are as we look to the future.
Currently, Carbon Dioxide levels are twice the historical average compared to the last 800,000 years and higher than has ever been recorded in history. This all the more impressive and worrisome when we consider that this deviation has occurred in less than 250 years. Furthermore, we have the capability of releasing extremely stable green house gases that could stay in the atmosphere for a duration of time equivalent to the creation of the Egyptian pyramids to present day.
Overall, we are changing the landscape of the planet. While the significance of green house gas emissions are under debate; we will need to understand to what extent each of these gases play a role in the environment and determine whether any action is needed to preserve the quality and security of life we enjoy today.